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“Skin cancers are by far the most commonly diagnosed cancer in the United States, so to prevent them, the public is constantly told to avoid the sun. However, while the relatively benign skin cancers are caused by sun exposure, the ones responsible for most skin cancer deaths are due to a lack of sunlight.”—A Midwestern Doctor, Dermatology’s Disastrous War Against The Sun, April 2024

With the quote above in mind, along with other relevant quotes from various sources, Unbekoming thought it was time to review and summarise the important book about sunlight ‘The Healing Sun: Sunlight and Health in the 21st Century’ (2000) by Richard Hobday.

The Healing Sun: 45 Questions and Answers

A summary of Richard Hobday’s book ‘The Healing Sun: Sunlight and Health in the 21st Century’ by Lies are Unbekoming.

Table of Contents

Question 1: What is heliotherapy and how was it historically used to treat diseases?

Heliotherapy is the therapeutic use of sunlight to prevent and treat various diseases. Historically, it was used to treat a wide range of conditions, including tuberculosis, wounds and bone disorders. In the early 20th century, physicians like Dr. Auguste Rollier developed specific protocols for exposing patients to sunlight gradually and carefully, often in combination with fresh air and proper nutrition. Heliotherapy was particularly popular before the advent of antibiotics and was used extensively during World War I to treat wounded soldiers.

Question 2: How does vitamin D synthesis occur in the body and what role does sunlight play in this process?

Vitamin D synthesis in the body occurs when ultraviolet B (“UVB”) radiation from sunlight penetrates the skin and converts a substance called 7-dehydrocholesterol into pre-vitamin D3. This pre-vitamin D3 then undergoes further changes over 2-3 days to become vitamin D3, which is carried via the bloodstream to the liver and kidneys to become the biologically active hormone 1,25 dihydroxyvitamin D3. Sunlight plays a crucial role in this process, as it is the primary source of the UVB radiation necessary for vitamin D synthesis. In many populations, sunlight exposure accounts for up to 90% of vitamin D production.

Question 3: What is the relationship between sunlight exposure and skin cancer risk?

The relationship between sunlight exposure and skin cancer risk is complex. While prolonged, intense sun exposure and sunburn, especially in childhood, can increase the risk of skin cancers like melanoma, some studies suggest that regular, moderate sun exposure may actually decrease the risk of melanoma. Basal cell and squamous cell carcinomas are more directly linked to cumulative sun exposure. However, the book emphasises that the dramatic increase in skin cancer rates over the 20th century coincided with people spending more time indoors, suggesting that other factors, such as diet and lifestyle, may play significant roles in skin cancer development.

Question 4: How does sunlight affect bone health and osteoporosis?

Sunlight plays a crucial role in bone health by enabling the body to produce vitamin D, which is essential for calcium absorption and bone formation. Adequate vitamin D levels help prevent osteoporosis and other bone disorders. The book mentions that there is a pronounced seasonal variation in bone density, with density being lowest during winter months when sunlight exposure is reduced. Additionally, hip fractures are more common in winter and at higher latitudes where there is less sunlight. Sunlight exposure, especially in childhood and adolescence, helps build strong bones and may reduce the risk of osteoporosis later in life.

Question 5: What was the role of sunlight therapy in treating tuberculosis before antibiotics?

Before the advent of antibiotics, sunlight therapy played a significant role in treating tuberculosis, especially forms affecting the bones, joints and skin. Physicians like Dr. Auguste Rollier developed specialised clinics in the Swiss Alps where patients were gradually exposed to sunlight in combination with fresh air, rest and proper nutrition. This approach, known as the “Rollier Method,” involved carefully controlled sunbathing sessions that increased in duration over time. The treatment was based on the observation that sunlight could kill the tuberculosis bacteria and stimulate the body’s natural healing processes. Many patients showed remarkable improvement, and some were even cured of their tuberculosis through this method.

Question 6: How can sunlight exposure help reduce hospital-acquired infections?

Sunlight exposure can help reduce hospital-acquired infections in several ways. Firstly, sunlight has a direct bactericidal effect, killing many harmful microorganisms. Studies have shown that sunlit hospital wards have fewer bacteria than dark wards. Secondly, UV radiation from sunlight can penetrate window glass and continue to have a disinfecting effect indoors. This was demonstrated in a study during World War II, where wards with unobstructed windows had significantly lower rates of respiratory infections compared to those with brick blast walls covering the windows. Additionally, sunlight exposure can boost patients’ immune systems, potentially making them more resistant to infections. Florence Nightingale recognised the importance of sunlight in hospitals and advocated for designs that maximised natural light and fresh air.

Question 7: What is Seasonal Affective Disorder and how is it related to sunlight exposure?

Seasonal Affective Disorder (“SAD”) is a form of depression that occurs during the winter months when sunlight exposure is reduced. It is characterised by symptoms such as low mood, fatigue, overeating (especially carbohydrates) and weight gain. SAD is directly related to decreased sunlight exposure, which can disrupt the body’s circadian rhythms and alter the production of hormones like melatonin and serotonin. These hormonal changes can affect mood, sleep patterns and energy levels. The condition is more common in regions farther from the equator where winter days are shorter. Treatment often involves light therapy, which mimics natural sunlight to help regulate the body’s internal clock and hormone production.

Question 8: What are the recommended practices for safe sunbathing?

Safe sunbathing practices, as recommended in the book, include gradual exposure to build up tolerance, avoiding midday sun (especially between 11 am and 3 pm), and not allowing the skin to burn. The book emphasises the importance of knowing one’s skin type and paying close attention to how it responds to sun exposure. Early morning sunlight is considered particularly beneficial. Hobday suggests sunbathing at temperatures below 18°C (64°F) for optimal health benefits. Wearing a hat to protect the face and neck is advised, as is starting with short exposures and gradually increasing duration. The book also recommends a diet rich in whole foods rather than refined foods to support skin health during sun exposure.

Question 9: How does building design impact sunlight exposure for occupants?

Building design significantly impacts sunlight exposure for occupants. The orientation of buildings, size and placement of windows, and design of outdoor spaces all affect how much natural light enters living and working areas. The book discusses how some historical designs, like Florence Nightingale’s hospital wards, prioritised sunlight exposure for health benefits. It also mentions that modern deep-plan office designs often rely on artificial lighting, reducing occupants’ exposure to natural light. Hobday argues for a return to designs that maximise sunlight exposure, suggesting features like sunlit balconies and verandas, especially in healthcare facilities and homes for the elderly. Proper building orientation can also help with passive solar heating and natural disinfection of spaces.

Question 10: What is the interaction between diet and sunlight in terms of health benefits?

The interaction between diet and sunlight is complex and significant for health. The book emphasises that a diet rich in whole foods, particularly those high in antioxidants like vitamins A, C and E, can enhance the body’s ability to benefit from sunlight exposure while reducing the risk of skin damage. Conversely, a diet high in refined foods and unhealthy fats may increase susceptibility to sun damage. Hobday cites research showing that a low-fat diet can reduce the incidence of non-melanoma skin cancers. Additionally, certain foods like fatty fish are rich in vitamin D, which can complement the vitamin D synthesised through sun exposure. The book also mentions that the traditional Japanese diet, high in vitamin D from fish, may explain lower rates of certain cancers in Japan despite its northern latitude.

Question 11: Who were some key historical figures in the development of sunlight therapy?

Key historical figures in the development of sunlight therapy include Niels Finsen, Auguste Rollier, and Oskar Bernhard. Niels Finsen, who won the Nobel Prize for Medicine in 1903, pioneered the use of ultraviolet light to treat tuberculosis of the skin. Auguste Rollier, often referred to as the “high priest” of sunlight therapy, developed a method of gradual sun exposure to treat tuberculosis at his clinics in the Swiss Alps. Oskar Bernhard was instrumental in using sunlight to treat war wounds during World War I. Florence Nightingale, while not directly involved in sunlight therapy, advocated for the importance of sunlight in hospital design for patient recovery.

Question 12: How did ancient civilizations utilise sunlight for therapeutic purposes?

Ancient civilisations recognised the healing power of sunlight and incorporated it into their medical practices. The ancient Greeks referred to sunbathing as “heliosis” and used it to treat various conditions including epilepsy, asthma and jaundice. They also practised “arenation,” which involved sand baths in the sun. The Romans, particularly figures like Pliny the Elder, considered sunbathing one of the best self-administered remedies. Ancient Egyptian pharaohs, such as Akhenaten, revered the sun for its life-giving properties and were depicted holding their children up to the Sun’s rays. These civilisations often combined sunlight therapy with other practices like hydrotherapy and exercise.

Question 13: What was the open-air treatment of diseases and how did it work?

The open-air treatment of diseases was a medical approach popularised in the late 19th and early 20th centuries, particularly for treating tuberculosis. It involved exposing patients to fresh, cold air and sunlight, often in sanatoria located in mountainous or coastal areas. The treatment was based on the observation that people who spent time outdoors were less susceptible to tuberculosis. Dr. George Bodington, an early proponent, argued that confining patients in warm, poorly ventilated rooms was detrimental to their health. The open-air method included rest, proper nutrition and gradual exposure to outdoor conditions. This approach was believed to stimulate the body’s natural healing processes, increase metabolism and strengthen the immune system.

Question 14: How does artificial lighting affect human health compared to natural sunlight?

Artificial lighting, particularly fluorescent lighting, can have negative effects on human health compared to natural sunlight. The book mentions that artificial light often fails to replicate the full spectrum of natural light, leading to potential disruptions in circadian rhythms and hormone production. Prolonged exposure to artificial light, especially at night, can suppress melatonin production, affecting sleep patterns and potentially increasing stress levels. Some studies have even suggested a link between fluorescent lighting and an increased risk of melanoma. Natural sunlight, on the other hand, provides a full spectrum of light that regulates various physiological processes, including vitamin D production, and has been shown to have mood-elevating effects. The book emphasises the importance of exposure to natural light for overall health and well-being.

Question 15: What is the connection between sunlight exposure and antibiotic resistance?

The book doesn’t directly discuss a connection between sunlight exposure and antibiotic resistance. However, it does mention that sunlight has natural bactericidal properties, which were utilised before the advent of antibiotics to treat infections and wounds. The emergence of antibiotic-resistant bacteria is discussed as a growing concern in modern healthcare, potentially leading to a return to some pre-antibiotic era practices. In this context, the book suggests that the germicidal properties of sunlight could become more important in hospital design and infection control if antibiotic resistance continues to increase. Hobday proposes that incorporating more sunlight into healthcare settings could help reduce the spread of infections, potentially decreasing reliance on antibiotics.

Question 16: How is sunlight utilised in Chinese traditional medicine?

In Chinese traditional medicine, sunlight is recognised as an important element for health and healing. The book mentions that the Chinese have a long tradition of taking exercise in the early morning sun, believing this practice allows practitioners to accumulate “biological energy” from the atmosphere. Traditional exercise systems like t’ai chi and qigong are often practised facing east towards the rising sun. The Chinese approach emphasises the importance of being outdoors at sunrise, exploiting the health-giving properties of the early morning environment. They believe that sunrise is the time of day with the greatest potential for health benefits, as the air is fresh and clear, and the body’s organs of elimination are most active. This practice is seen as integral to their medical system and preventive health approach.

Question 17: What is the relationship between sunlight exposure and multiple sclerosis?

The book describes a significant inverse relationship between sunlight exposure and the incidence of multiple sclerosis (“MS”). Studies have shown that the risk of developing MS increases dramatically with latitude, meaning areas farther from the equator (with less sunlight) have higher rates of the disease. Exposure to sunlight in childhood and adolescence appears to have a protective effect against developing MS in later life. This relationship is thought to be linked to vitamin D production, as areas with naturally high vitamin D intake (like coastal Norway, where fish consumption is high) have lower MS rates than would be expected based on latitude alone. The book suggests that the Sun’s rays may act on the immune system to prevent the inflammation in the retina and brain that is thought to be the first stage in the development of MS.

Question 18: How does sunlight exposure impact heart disease risk?

Sunlight exposure appears to have a protective effect against heart disease. The book mentions several mechanisms through which this may occur. Firstly, sunlight exposure has been shown to lower blood pressure, with studies demonstrating that ultraviolet radiation can significantly reduce both systolic and diastolic pressure. Secondly, sunlight helps lower blood cholesterol levels, which is a major risk factor for heart disease. The book notes that cholesterol levels tend to be higher in populations at higher latitudes and show seasonal variation, increasing in winter when sunlight exposure is reduced. Additionally, sunlight exposure is associated with increased cardiac output and improved blood oxygenation. The book suggests that lack of sunlight may be a potential risk factor for coronary heart disease, particularly among less affluent populations and certain immigrant groups who may have limited outdoor exposure.

Question 19: Can sunlight exposure play a role in cancer prevention?

Yes, the book suggests that sunlight exposure may play a significant role in cancer prevention, particularly for internal cancers. While acknowledging the link between excessive sun exposure and skin cancer, the book presents evidence that moderate sunlight exposure might help prevent several types of cancer, including breast, colon, prostate and ovarian cancer. This protective effect is thought to be largely due to vitamin D production stimulated by sunlight. Studies have shown an inverse relationship between sunlight exposure and cancer mortality rates, with lower cancer rates in sunnier regions. The book cites research estimating that regular moderate sunbathing could result in approximately a one-third reduction in breast and colon cancer death rates.

Question 20: What are the potential benefits and risks of using sunscreens?

The book presents a nuanced view of sunscreens, acknowledging both potential benefits and risks. The primary benefit of sunscreens is their ability to prevent sunburn, which is a risk factor for skin cancer. However, the book raises several concerns about their widespread use. One issue is that sunscreens may give users a false sense of security, leading to prolonged sun exposure that could increase skin cancer risk. Some studies suggest that sunscreen use might be associated with an increased risk of melanoma, possibly due to altered ratios of UVA to UVB exposure. Sunscreens also block the skin’s ability to produce vitamin D, which could lead to deficiency and associated health problems. Additionally, some chemical compounds in sunscreens have raised health concerns. The book suggests that while sunscreens can be useful for preventing burn in strong sunlight, they should not be relied upon as the primary form of sun protection, and their routine daily use may not be beneficial for overall health.

Question 21: How does ozone depletion affect UV radiation and human health?

The book challenges some common assumptions about ozone depletion and its effects on human health. While it acknowledges that the ozone layer is being depleted by atmospheric chemicals, it states that there’s no evidence of any long-term increase in UVB radiation in densely populated regions. The feared consequences of ozone depletion, such as increases in skin cancers, eye diseases and immune system disorders, have not been observed. The book cites a study in Punta Arenas, Chile, near the Antarctic ozone hole, which found no ozone depletion-related health problems. It suggests that the increase in skin cancer rates predates and is unrelated to ozone depletion. Hobday argues that focusing on ozone depletion may divert attention from more significant factors affecting skin cancer rates, such as changes in lifestyle and diet.

Question 22: What is the relationship between indoor air quality and sunlight exposure?

The book emphasises a strong connection between indoor air quality and sunlight exposure. Sunlight, particularly its ultraviolet component, has natural disinfecting properties that can improve indoor air quality by killing bacteria and other microorganisms. Buildings designed to admit more sunlight tend to have lower levels of airborne pathogens. Hobday cites historical examples, such as Florence Nightingale’s hospital designs, which prioritised sunlight and fresh air to reduce infections. Modern, sealed buildings with little natural light may have poorer air quality and higher rates of bacterial growth. The book suggests that reincorporating sunlight into building design could help address issues of indoor air pollution and reduce the spread of infections, especially in healthcare settings.

Question 23: How does sunlight influence circadian rhythms?

Sunlight plays a crucial role in regulating circadian rhythms, the body’s internal 24-hour cycle. The book explains that the sun’s daily cycle of light and dark regulates many of the body’s hormonal and biochemical processes. Light entering the eye stimulates the hypothalamus, which controls the production of hormones like serotonin and melatonin. These hormones regulate sleep patterns, body temperature and mood. Without regular exposure to natural light cycles, the body’s internal clock tends to “free run” on a cycle closer to 25 hours, which can disrupt normal patterns of waking and sleeping. The book notes that modern indoor lifestyles with artificial lighting can interfere with these natural rhythms, potentially contributing to conditions like Seasonal Affective Disorder (“SAD”) and other health issues.

Question 24: What effects does sunlight have on blood pressure and cholesterol levels?

Sunlight exposure has been shown to have significant effects on both blood pressure and cholesterol levels. The book cites studies demonstrating that ultraviolet radiation can lower blood pressure in both normal people and those with hypertension. This effect is particularly pronounced in the summer months when solar radiation is strongest. Regarding cholesterol, the book explains that sunlight is necessary for the body to break down cholesterol. In the absence of sufficient sunlight, squalene in the skin is converted to cholesterol instead of vitamin D, potentially leading to higher blood cholesterol levels. The book notes a seasonal variation in blood cholesterol levels, with higher levels observed in winter months when sunlight exposure is reduced. These findings suggest that regular sunlight exposure could be an important factor in maintaining healthy blood pressure and cholesterol levels.

Question 25: How prevalent is vitamin D deficiency in different populations?

The book indicates that vitamin D deficiency is surprisingly prevalent across various populations, particularly in developed countries. In Europe, a study found that over a third of 70-year-olds are deficient in vitamin D during winter months. The problem is not limited to the elderly; the book cites a study of young men on normal diets who became vitamin D deficient after just six weeks without sunlight exposure. Certain groups are at higher risk, including people with darker skin living in northern latitudes, those who spend most of their time indoors and people who cover most of their skin when outdoors. The book suggests that vitamin D insufficiency or deficiency might be more widespread in the general population than previously thought, with one study finding 66% of patients in a general medical ward to be deficient. This prevalence is attributed to modern lifestyles that involve less time outdoors and more time in artificially lit environments.

Question 26: How did Florence Nightingale’s hospital designs incorporate sunlight, and why?

Florence Nightingale’s hospital designs prominently incorporated sunlight as a key element for patient health and recovery. She advocated for what became known as “pavilion plan” hospitals, which consisted of single-story ward blocks with extensive glazing on both sides. This design allowed for cross-ventilation and admission of ample fresh air and sunlight. Nightingale believed that sunlight had therapeutic properties and was essential for preventing the spread of infections. Her wards were designed with a minimum of one large window for every two beds, ensuring patients had access to natural light. She insisted on natural ventilation and open fireplaces, rejecting artificial heating and ventilation systems as unhealthy. Nightingale’s designs were based on her belief in the “zymotic theory” of infection, which held that diseases could be spread through contaminated air. By maximising sunlight and fresh air, she aimed to create a healing environment that would disperse “noxious emanations” and prevent cross-infection among patients.

Question 27: What is the relationship between exercise and sunlight exposure?

The book describes a synergistic relationship between exercise and sunlight exposure. Studies have shown that exercise combined with sun exposure has a greater effect on stamina, fitness and muscular development than exercise alone. This relationship was recognised in ancient practices, such as the Greeks exercising nude outdoors. The book notes that sunlight increases both the oxygen content of human blood and its capacity to deliver oxygen to tissues, similar to the effects of regular exercise. Additionally, both exercise and sunlight exposure can lower blood sugar levels, which is particularly noticeable in diabetics. In Chinese traditional medicine, exercises like t’ai chi and qigong are often practised outdoors at sunrise, combining the benefits of physical activity with early morning sunlight exposure. The book suggests that this combination may be particularly effective for overall health and longevity.

Question 28: How is sunlight therapy used to treat skin conditions like psoriasis?

Sunlight therapy, or heliotherapy, has been found to be particularly effective in treating psoriasis. The book describes how patients with psoriasis often benefit from controlled exposure to natural sunlight, sometimes in combination with other therapies. For instance, at the Dead Sea in Israel, the high mineral content of the water combined with solar radiation has been shown to improve the condition in about 80% of patients who receive treatment there. The book also mentions a study where Finnish patients with severe psoriasis were sent to the Canary Islands for four weeks of heliotherapy, which proved cost-effective for cases that would otherwise require regular hospital admissions or outpatient treatments. The UV radiation in sunlight appears to have an anti-inflammatory effect and can help slow the rapid cell division characteristic of psoriasis. However, the book emphasises that such treatments should be carried out under medical supervision to ensure safety and effectiveness.

Question 29: How do demographic changes impact healthcare for the elderly in relation to sunlight exposure?

The book discusses how demographic changes, particularly the ageing of populations in developed countries, are increasing the importance of sunlight exposure in elderly healthcare. With more people living longer, there’s a growing need to address age-related health issues, many of which are influenced by vitamin D levels and sunlight exposure. The elderly are at higher risk of vitamin D deficiency due to decreased skin efficiency in producing vitamin D, reduced outdoor activity and sometimes dietary deficiencies. This can lead to an increased risk of osteoporosis, fractures and other health problems. The book suggests that healthcare strategies for the elderly should include ways to ensure adequate sunlight exposure, such as incorporating sunlit spaces in care homes and encouraging outdoor activities. It also notes that the Chinese approach to ageing, which includes early morning outdoor exercises like t’ai chi, could be beneficial if adopted more widely in Western countries.

Question 30: What are t’ai chi and qigong and how do they relate to sunlight exposure?

T’ai chi and qigong are traditional Chinese exercise systems that are often practised outdoors, particularly at sunrise. The book describes these practices as ways to accumulate “biological energy” from the atmosphere, combining physical movement with the health benefits of early morning sunlight exposure. T’ai chi ch’uan, developed as a martial art, involves slow, graceful movements that require mental focus and are believed to balance the body’s energy. Qigong includes various practices focusing on breath control and meditation. Both are traditionally practised facing east, towards the rising sun. The book suggests that these exercises, when performed regularly in the morning sunlight, may contribute to improved balance, cardiovascular health and overall well-being, particularly in older adults. The combination of gentle exercise and sunlight exposure is seen as particularly beneficial in preventing falls and maintaining mobility in the elderly population.

Question 31: What are rickets and osteomalacia, and how are they related to sunlight exposure?

Rickets and osteomalacia are conditions caused by vitamin D deficiency, which is directly related to lack of sunlight exposure. Rickets affects children, causing softening and weakening of bones, leading to deformities such as bowed legs and curved spines. Osteomalacia is the adult equivalent, resulting in softened bones and an increased risk of fractures. The book explains that these conditions were once widespread in industrialised areas due to air pollution blocking sunlight and poor living conditions keeping people indoors. Contrary to popular belief, the book emphasises that rickets and osteomalacia are primarily “diseases of darkness” rather than dietary deficiencies. Adequate sunlight exposure can prevent and even cure these conditions by enabling the body to produce sufficient vitamin D, which is crucial for calcium absorption and bone formation.

Question 32: How does sunlight exposure affect diabetes?

Sunlight exposure appears to have beneficial effects on diabetes management. The book mentions that sunlight, like regular exercise, can lower blood sugar levels. This effect is particularly noticeable in diabetics, who may need to adjust their insulin dosage when exposed to strong sunlight for extended periods. The mechanism isn’t fully explained, but it’s suggested that sunlight may improve insulin sensitivity or stimulate the pancreas to produce more insulin. Additionally, vitamin D, which is produced in the skin through sunlight exposure, has been linked to improved glucose metabolism. The book also notes that some studies have shown vitamin D supplementation in infancy may protect against or arrest the initiation of insulin-dependent diabetes in later childhood, suggesting that early life sunlight exposure might play a role in diabetes prevention.

Question 33: What is the relationship between sunlight exposure and breast, colon, ovarian and prostate cancers?

The book presents evidence suggesting an inverse relationship between sunlight exposure and the incidence of breast, colon, ovarian and prostate cancers. Studies have shown that mortality rates from these cancers tend to be lower in sunnier regions and increase with distance from the equator. For instance, breast and colon cancer rates are 4-6 times lower in regions within 20 degrees of the equator compared to northern Europe or North America. The protective effect is thought to be largely due to vitamin D production stimulated by sunlight. The book cites research estimating that regular moderate sunbathing could result in approximately a one-third reduction in breast and colon cancer death rates. For prostate cancer, the highest rates occur in northern latitudes, and studies have shown a significant north-south trend with lower mortality rates in sunnier areas. Similarly, ovarian cancer mortality has been found to be inversely associated with Sun exposure. The book suggests that vitamin D’s role in cell growth regulation and its potential anti-cancer properties may explain these relationships.

Question 34: How does sunlight impact the immune system?

Sunlight has a complex and significant impact on the immune system. The book explains that moderate sunlight exposure can strengthen the immune system in several ways. Ultraviolet radiation from sunlight has been shown to increase the number of white blood cells in human blood, particularly lymphocytes, which play a major role in defending the body against infections. Sunlight also stimulates the production of vitamin D, which is crucial for immune function. The book mentions that sunlight exposure can speed up the elimination of toxic chemicals from the body and has been used historically to treat various infectious diseases, including tuberculosis. However, it’s also noted that excessive Sun exposure can suppress immune function, potentially increasing susceptibility to certain infections. The balance between these effects underlies the importance of moderate, controlled Sun exposure for optimal immune health.

Question 35: What was the window tax and how did it affect building design and health?

The window tax was a property tax imposed in England in 1696 that was based on the number of windows in a house. The book explains that this tax had a significant impact on building design and, consequently, on public health. To avoid the tax, many homeowners bricked up windows, and new houses were often designed with fewer windows. This trend continued even after the tax was abolished in 1851. The reduction in windows led to decreased natural light and ventilation in buildings, which had negative health consequences. Lack of sunlight and fresh air in homes contributed to the prevalence of diseases like rickets and tuberculosis. The book uses this historical example to illustrate how government policies can inadvertently affect public health through their impact on building design and sunlight exposure.

Question 36: How does sunlight exposure affect dental health?

The book presents some interesting historical evidence on the relationship between sunlight exposure and dental health. A study from 1939 involving 94,000 American males aged 12-14 showed a clear correlation between sunlight exposure and tooth decay. Children living in the northeast of the USA, where mean annual sunlight was less than 2,200 hours per year, had two-thirds more cavities than those living in the southwest, where annual sunlight exceeded 3,000 hours. Another study from 1938 found that the incidence of dental caries among American children varied seasonally, with the highest incidence in late winter and early spring, and very low values during summer months. The book suggests that this relationship might be due to vitamin D production stimulated by sunlight, which plays a role in calcium metabolism and tooth mineralisation. Based on this information, Hobday even suggests that it might be beneficial to schedule routine dental appointments in early autumn when vitamin D levels are highest and teeth are strongest.

Question 37: What is the “vitamin D winter” and why is it important?

The “vitamin D winter” refers to the period of the year when sunlight is not strong enough to stimulate vitamin D production in the skin. In countries far from the equator, such as Britain, this occurs from October to March. During these months, the UVB radiation necessary for vitamin D synthesis doesn’t reach the Earth’s surface in sufficient quantities. This concept is important because it highlights the seasonal nature of natural vitamin D production and explains why many people in northern latitudes may become deficient in vitamin D during winter months. The book emphasises that people need to build up vitamin D reserves during the summer months to last through the winter. Understanding the “vitamin D winter” is crucial for public health strategies, as it underscores the need for either increased dietary vitamin D intake or supplementation during these months to maintain adequate levels of this essential nutrient.

Question 38: How does sunlight exposure during pregnancy affect foetal development?

The book discusses several ways in which sunlight exposure during pregnancy can affect foetal development. One striking finding is that children born in the spring tend to be taller as adults compared to those born in the autumn. This is attributed to variations in sunlight levels during the latter stages of pregnancy influencing growth. The book explains that sunlight may regulate the amount of growth hormone in the mother’s bloodstream, which in turn affects foetal development. Additionally, vitamin D produced through sunlight exposure is crucial for foetal bone development. The book also mentions an ancient Egyptian hymn that attributes the placement of “male seed in woman” and the quickening of the foetus to the sun, suggesting a long-standing recognition of sunlight’s importance in reproduction and foetal development. However, the book also cautions that excessive sun exposure during pregnancy can be harmful, emphasising the need for balanced and moderate exposure.

Question 39: How was sunlight used to disinfect wounds, particularly during wartime?

Sunlight was used extensively to disinfect and heal wounds, especially during World War I. The book describes how military surgeons utilised sunlight therapy clinics to treat wounded soldiers. Dr. Oskar Bernhard, a pioneer in this field, developed a method of exposing wounds directly to sunlight. He found that sunlight had a powerful disinfecting effect, helping to clean wounds and speed up the healing process. Bernhard’s technique involved removing dressings and exposing wounds to the sun for several hours daily, gradually increasing exposure time. This method was particularly effective in treating compound fractures and infected wounds. The book notes that sunlight therapy was crucial in an era before antibiotics when conventional treatments often failed to prevent infections. Sunlight’s ability to kill bacteria and stimulate the body’s healing processes made it a valuable tool in treating war wounds and preventing complications like gangrene.

Question 40: How does air pollution impact sunlight exposure and its health benefits?

Air pollution significantly impacts sunlight exposure and its health benefits by filtering out or blocking ultraviolet radiation. The book discusses how air pollution, particularly from industrial sources, can create a persistent layer of haze that reflects UV radiation. This was a major factor in the high prevalence of rickets in industrialised areas during the 18th and 19th centuries. Sulphur dioxide from coal burning was especially effective at blocking the UVB rays necessary for vitamin D synthesis. Even in modern times, the book suggests that air pollution in urban areas may contribute to vitamin D deficiency and related health problems. Hobday notes that moving from an urban to a rural, alpine or seaside location can result in greater UV exposure simply due to cleaner air. This relationship between air quality and effective sunlight exposure underscores the importance of considering environmental factors when assessing the potential health benefits of sunlight in different regions.

Question 41: What are the differences between UVA and UVB radiation, and how do they affect human health?

UVA (320-400 nm) and UVB (290-320 nm) are two types of ultraviolet radiation that reach the earth’s surface and affect human health in different ways. UVB burns skin more rapidly than UVA but doesn’t penetrate as deeply. UVB is primarily responsible for sunburn and plays a crucial role in vitamin D synthesis in the skin. It’s also more strongly linked to the development of skin cancers. UVA, once thought to be relatively safe, penetrates more deeply into the skin and is now known to contribute to premature skin ageing and wrinkling. Recent research suggests UVA may also play a role in the development of melanoma. Importantly, UVA can penetrate window glass, while UVB cannot. The book emphasises that both types of radiation contribute to tanning and burning, and that a balance of exposure is necessary for health benefits while minimising risks.

Question 42: How does sunlight exposure affect melatonin production?

Sunlight exposure has a significant impact on melatonin production, which in turn affects sleep patterns and overall health. Melatonin is produced by the pineal gland and its secretion is suppressed by light, particularly the blue light spectrum found in sunlight. During the day, when exposed to sunlight, melatonin production is inhibited. As darkness falls, melatonin levels rise, inducing sleep and slowing down physiological processes. The book explains that disruptions to this natural cycle, such as prolonged exposure to artificial light or lack of sunlight during the day, can lead to sleep disorders and other health issues. Understanding this relationship is crucial for maintaining healthy circadian rhythms. The book suggests that getting regular sunlight exposure, especially in the morning, can help regulate melatonin production and improve sleep quality.

Question 43: What is the relationship between latitude and various health conditions?

The book presents evidence of a strong relationship between latitude and the prevalence of various health conditions. Generally, as distance from the equator increases (i.e., at higher latitudes), there’s a higher incidence of several diseases. This pattern is observed in conditions such as multiple sclerosis, certain types of cancer (including breast, colon and prostate) and osteoporosis. For example, the risk of multiple sclerosis increases dramatically with latitude, and cancer mortality rates tend to be higher in northern regions compared to areas closer to the equator. The book attributes this largely to differences in sunlight exposure and subsequent vitamin D production. However, it’s noted that other factors such as diet (e.g., high fish consumption in some northern coastal areas) can sometimes mitigate these latitude-related health trends. Hobday suggests that understanding these geographical patterns could have important implications for public health strategies, especially in regions with limited sunlight.

Question 44: What are the benefits and risks of using sunlamps and solaria?

The book presents a balanced view of sunlamps and solaria, acknowledging both potential benefits and risks. Benefits include the ability to stimulate vitamin D production, especially during winter months or for people who cannot get regular sun exposure. Sunlamps can also be used to treat certain skin conditions and Seasonal Affective Disorder (“SAD”). However, the risks are significant. Many modern sunbeds emit a high proportion of UVA radiation, which was once thought to be safer but is now known to contribute to skin ageing and potentially increase melanoma risk. The book warns against using sunbeds for cosmetic tanning, as this can lead to overexposure and increased skin cancer risk. It suggests that if artificial UV sources are used, they should mimic natural sunlight as closely as possible and be used under guidance. Hobday recommends short, controlled exposures for health benefits rather than aesthetic reasons, emphasising that natural sunlight, when available, is preferable.

Question 45: How does clothing impact vitamin D synthesis in the body?

Clothing has a significant impact on vitamin D synthesis in the body by acting as a physical barrier to UVB radiation. The book explains that different types of fabric vary in their ability to block UV rays. For example, black wool blocks over 98% of incident UVB radiation, while white cotton allows about 50% to pass through. Even with more permeable fabrics, several minimal erythemal doses (“MEDs”) of UV exposure would be required before vitamin D synthesis could occur. The book notes that in some cultures where traditional dress covers most of the body, such as with Bedouins in the Negev desert or certain immigrant populations in Western countries, vitamin D deficiency can be common despite living in sunny climates. This underscores the importance of exposing bare skin to sunlight for adequate vitamin D production. Hobday suggests that understanding the impact of clothing on vitamin D synthesis is crucial for developing appropriate health guidelines, especially for populations that traditionally cover most of their skin.