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See Also

The Chemical Sunscreen Health Disaster
What is Suntanning and is it Dangerous?
Sensible Suntanning, Vitamins that Help, and Safer Sunscreens
Types of Ultraviolet Radiation (UV)
Types of Sunscreens and SPF Ratings
Use Pure, Non-Encapsulated Reflective Physical Sunblockers
Vitamin A/Retinol May Protect from Sun Damage
Sunlight, Skin Damage and Cancer
Does Sunlight Exposure Increase or Decrease Cancer?
Does Sunlight Reduce Breast, Colon, Ovarian and Prostate Cancer?
Cholecalciferol: the Sunlight "Vitamin"
Sunlight Increases Sexuality and Mental Health
Sunlight Exposure may Reduce Schizophrenia in Newborns
Sunlight as a Treatment for Psoriasis
Special Sunlight Sensitivities
Sunscreen Options

"If you're planning to smear on the suntan lotion this summer, here's the real rub: new research shows that the active ingredients in some sunscreens can cause genetic damage."
        From: The Scientist, March/April 1999, page 7.
 

Sunlight and Health

A certain amount of sunlight on your skin may be necessary for good health. Sunlight activates a gene called pom-C, which in turn helps create melanin that determines skin color and enhances sex drive, the endorphins or “happiness hormones”, and leptin, which helps burn fat to keep you thin. In the USA, people who have high sunlight exposure (farmers, mail carriers) live the longest. The key is to find methods to receive adequate sunlight exposure while reducing skin damage.

Why Do People Suntan?

The most common reason for given for suntanning is that time in the sun brings a psychological feeling, often intense, of well being and relaxation. The physical warmth of the suns rays also is very pleasant. After becoming more tan, most people feel better about themselves. These are deep psychological feelings and seem to be part of our genetic response to sunlight.

What is Suntanning and is it Dangerous?

An estimated 22 million Americans tan in salon sun beds each year and a much larger number tan outside every year. Suntanning slowly produces pigment (melanin) in the skin as ultraviolet rays in sunlight penetrate the skin. The buildup of melanin helps to blocks ultraviolet rays and also serves as a powerful anti-oxidant. Additional, sunlight produces a redness or erythema that when combined with melanin results in the esthetically preferred skin color tone.

People suntan for a variety of  reasons - to enhance physical beauty and sexual attractiveness, for mood elevation. and to counter depression.  Some use sunlight to improve skin health as with psoriatic lesions.

But is light suntanning healthy or dangerous? Consider the following:

* Humans evolved in the presence of abundant sunlight. Geneticists and archeologists calculate that humans lost their body hair 1.2 million years ago but only started wearing clothes 72,000 years ago. So for about 1,128,000 years our ancestors frolicked nude in the Garden of Eden and thrived.

* USA cancer rates are highest in the northern states with the least sunshine.

* Rates of breast, prostate, ovarian, rectal and colon cancer are drastically lower persons with more sunlight exposure.

* Sunlight exposure may reduce breast cancer of 30 to 40% and ovarian cancer by 80%.

* It is calculated that there are 2,200 sunlight associated cancer deaths yearly vs. 138,000 for the above cancers in the USA.

* Sunlight associated cancers (non-melanoma) increase most where sunscreens are most heavily promoted.

* Sunlight raises positive moods in persons with SAD (seasonal affective disorder).

* Psoriatic skin lesions are reduced by sunlight.

* Sunlight raises testosterone levels in males.

* Sunlight exposure may reduce schizophrenia in newborns.

* Multiple sclerosis is much lower in areas with more sunlight exposure.
 

Despite the medical establishment's near unanimity (with the exception of many cancer research scientists) on the issue of sunlight exposure, serious health errors have been promoted to the public in the past.

    1. In 1927, 12,745 physicians endorsed smoking Lucky Strike cigarettes as a healthful activity. In the 1940s and 1950s, thousands of prominent surgeons were used in national cigarette advertisements to reassure the public about the safety of cigarette smoking.

    2. In the 1950s, lobotomies were promoted for mental disorders and produced near-totally dysfunctional people.

    3. In the 1960s and 1970s, diets high in omega-6 polyunsaturated fats and partially hydrogenated fatty acids such as safflower oil and margarine were recommended to reduce heart disease. However, long term studies found that, while such diets decreased heart disease, they increased the total death rate and the cancer rate and produced accelerated aging.

    4. For the past 30 years, cosmetic companies and a small group of very vocal, publicity-seeking dermatologists have strongly advocated that chemical sunscreens should be heavily applied before any exposure to sunlight. They insisted that such sunscreen use would prevent skin cancer and protect your health. This was despite of a lack of any adequate safety testing of these chemicals. (It should be emphasized that most dermatologists are much more cautious and careful)

Now it is know that many of such sunscreens have strong estrogenic activity like many banned toxic chemicals such as PCBs, DDT, and dioxin. See  The Chemical Sunscreen Health Disaster.

    5. While it is established that excessive sun exposure will produce serious skin damage, it is also possible that we need some minimum amount of sunlight to maintain good health and a positive mental state. Sitting in a dark room for years did not help the brilliant industrialist and movie producer, Howard Hughes. Sunlight produces vitamin D in the skin (and probably other unknown molecules) and also strongly affects pineal gland function - considered one the the master glands controlling body function.
 

But how much sunlight is needed?  Studies have found that 20 to 30 minutes per day supplies the required amount of vitamin D. On the other hand, persons afflicted with depression from SAD (seasonal affective disorder) often need several hours of full spectrum lighting to alleviate depression.
 

Sensible Suntanning

Moderate suntanning (20 to 30 minutes maximum per day) over a number of days produces better results. As pigment (melanin) builds in the skin it adds to your skin protection.  Dr. Martin Rieger has discussed the chemistry of oxidation and peroxidation in his publications. He emphasizes that melanin, the skin's pigment, is also a free radical scavenger, and somewhat "photo-protective" in a way that is unrelated to its light-scattering ability. In addition, the skin's natural defenses against oxygen radicals include other anti-oxidants such as Vitamin E and beta-carotene, and the copper-containing protein, superoxide dismutase, all of which de-toxify oxygen radicals and reduce skin damage.

Remember, excessive sun exposure can overwhelm the protective systems in the skin, causing skin damage that produces skin peeling and other types of damage. Dr. Lester Packer (University of  California, Berkeley) has published extensively on the role played by antioxidants such as Vitamin  E and skin protection. His research found that after absorbing in the UVB  radiation from sunlight spectrum, vitamin E is transformed into a free radical (tocopheroxyl) which can regenerate back to vitamin E (tocopherol) via reaction with the skin's vitamin C (ascorbic acid).  Packer's  hypothesis is that as ultraviolet radiation dosage is gradually increased, these two antioxidant defenses of the skin are overwhelmed. Then free radicals begin to form in the skin and cause various types of cellular damage, including lipid peroxidation and oxidative modification of skin proteins and cellular DNA. Packer has measured the depletion of cutaneous lipid soluble antioxidants (such as Vitamin  E) after ultraviolet radiation of the skin. For example, 45 minutes of exposure to the noon-day sun can lower the skin's protective vitamin C levels by 80% and also markedly lower other protective skin anti-oxidants such Vitamin E and beta-carotene. Packer also finds that sunblockers reduce this depletion of dermal antioxidants.

Also keep in mind that after suntanning, it takes the melanocytes 2 to 5 days to produce the pigment that provides some protection against burning. In contrast, burning can occur in a few hours in the sun. Development of a tan takes several days and cannot be rushed. In addition, sun exposure causes a thickening of the  top epidermal layer of the skin and this increases your resistance to burning.
 

If you tend to sunburn or plan an extended time in sunlight, take anti-oxidant supplements starting five days before the sunlight exposure. Studies have found that both the topical application of anti-oxidants and the ingestion of supplemental anti-oxidants reduce sun damage.

The following supplements have been recommended by skin researchers. (Source: Drug and Cosmetic Industry, September 1997, pages 52-55 and December 1997, pages 40-44.)
 
 

Anti-Oxidant Supplements That Reduce Suntanning Damage

	Dosage per day
Beta-carotene	30 mg
Mixed carotenoids from algae	50 mg	Contains beta-carotene, cytoxanthin and xanthin, alpha carotene, leutin
Natural vitamin E (Do not use pure d-alpha - it blocks the protection of  the d-gamma form - gamma is the best protector)	400 units	Contains d-alpha-tocopherol, d-beta-tocopherol, d-gamma tocopherol, d-delta tocopherol
Vitamin C	1 gram

Skin Types and Sun Exposure

Children in general are very sensitive to sunlight and have very thin skin that burns quickly but tans slowly. They should not be exposed to sunlight for more than 5-10 minutes. Infants (under 1 year) should not be exposed to intense sunlight at all.

 Persons with very light skin, reddish hair and lots of freckles are most sensitive to sunlight. They may burn very quickly and tan very slowly. People with this type of complexion should avoid unprotected exposure to intense sunlight of longer than 20 minutes.

Light skin, in persons who are blond or strawberry blonde and often freckled also burns quickly and tans slowly. People with this complexion should avoid unprotected exposure to intense sunlight of longer than 20 to 30 minutes. Darker skin tones are more protective against sunlight but remember that even the darkest complexion doesn't make you immune to sunburn.

Protective clothing and a wide brimmed hats can protect when you are outside. Remember that UV rays are present even on cloudy days. Sunlight is strongly reflected from sand, snow, ice, and concrete and can increase your direct sunlight exposure up to 50%.

Wear sunglasses that filter out ultraviolet light to protect your eyes.

Be especially careful about sun exposure if you take medications like tetracycline, antihistamines, "sulfa" drugs, diuretics and some oral contraceptives. The combination of some drugs and sunlight can decrease the time needed to produce sunburn. (See below Special Sunlight Sensitivities)

Types of Ultraviolet Radiation (UV)

Suntans are produced by two types of ultraviolet radiation in sunlight.

UVA rays constitute 90-95% of the sun's ultraviolet light reaching the earth and have a relatively long wavelength (320-400 nm) directly adjoining the violet end of the visible light spectrum. UVA light penetrates the furthest into the skin and is the primary inducer of tanning response in humans

UVB rays are partially absorbed by the ozone layer and have a medium wavelength (290-320 nm). They do not penetrate the skin as far as the UVA rays do but contain more energy and activate the synthesis of vitamin D and the absorption of calcium and other minerals. UVB rays are the primary cause of sunburn and of the most concern for skin and eye damage.

Types of Sunscreens and SPF Ratings

The ability of a sunscreen to protect the user from UVB is defined as its Sun Protection Factor (SPF).  The SPF is the ratio of the amount of ultraviolet radiation required to produce minimal pinkness (erythema) in skin covered by a sunscreen, assessed 24 hours after exposure, to the amount of UV radiation required to produce a similar level of pinkness in unprotected skin. If a sunscreen reduces the effect of sunlight on skin by 50% it would have an SPF of 2, if by 75%, the SPF would be 4, and so on. Most sunscreens have SPF ratings from four to as high as 40 or 50. The level of protection from ultraviolet radiation provided by the product increases as the value of the SPF rating increases.

The SPF applies for UVB rays only. The protection provided against UVA rays in chemical sunscreens is about 10% of the UVB rating.

An SPF of 15 will provide 15 times the amount of protection you'd get without using anything.  Thus, if 10 minutes in the sun is enough to turn you red, your sunscreen would allow you to stay out for 150 minutes before burning.  An SPF of 15 filters approximately 92% of the sun burning rays.  For UVA the degree of protection is defined as the Phototoxic Protective Factor (PPF).  These values are much lower, ranging from 1.5 - 4.8, because the energy contained in UVA is so much less.

Sunscreens are designed to protect against sunburn (UVB rays) and generally provide little protection against UVA rays.

Recommended Sunscreens

Physical Reflective Sunblockers contain inert minerals such as titanium dioxide, zinc oxide, red petrolatum, or talc and work by reflecting the ultraviolet (UVA and UVB) rays away from the skin. They come in two forms - pure sunblocker and various micronized or encapsulated versions.

The best overall reflective sunblocker, at least in theory, is pure titanium dioxide. Zinc oxide has somewhat better UVA and UVB blocking but also can generate free ionic zinc ions on the skin. Some women think zinc oxide increases facial pore size. Since copper complexes are used by the body for skin regeneration and remodeling, the generation of zinc ions could displace copper ions and reduce the rate of skin renewal.

One problem with titanium dioxide is that it is whiter than zinc oxide and more difficult to formulate as a transparent products. Thus you may prefer zinc oxide products.

Use Pure, Non-Encapsulated Reflective Physical Sunblockers

The safest pure physical sunscreens that contain inert minerals such as titanium dioxide or zinc oxide.   Pure sunblockers tend to give a pasty look to the skin. This is the reason for the popularity of micronized sunblockers which give a better cosmetic appearance on the skin.

Avoid Micronized or Siliconized Physical Sunscreens.

Prof. Nicholas Lowe (Dermatology, UCLA) has reported that micronized or encapsulated physical sunblockers such as titanium dioxide penetrate into the skin while pure titanium dioxide remains on the skin's surface - where you really want it to stay.

Do Physical Sunblockers Generate Free-Radicals?

There have been reports that physical sunblockers can also generate free radicals after exposure to ultraviolet. However, even bare skin will generate free radicals when exposed to UV radiation. The key is whether the sunblocker form will penetrate the skin and be near the skin's sensitive proteins and DNA. Pure sunblockers such as zinc oxide and titanium dioxide do not pass into the skin and remain far from the skin's sensitive areas. However, sunblockers that are micronized and coated with plastics or silicone more easily pass the skin barrier and can reach the skin's sensitive areas. For this reason, pure physical sunblockers are the safest.

Not Recommended - Free Radical Generators and Estrogenic Chemicals

Chemical sunscreens act by strongly absorbing ultraviolet light in the UVB range (290 to 320 nm). They cannot reflect light. The UVB range is the range that is primarily responsible for sunburning and causing skin cancer. The UVA range (320 to 400 nm) is responsible for suntanning and photosensitivity reactions (increased sensitivity to sunlight as the result of certain medications, cosmetics, soaps, or plants). UVA is also responsible for serious skin damage. Such types of chemical sunscreens are potent generators of free radicals and many have strong estrogenic, "gender bending", activities and may increase your cancer risk for cancers of the breast, ovaries, prostate, and colon (see more below). PABA and PABA esters are rarely used today because of allergic problems.

Chemical Sunscreens Include:

Benzophenones (dixoybenzone, oxybenzone)

PABA and PABA esters (ethyl dihydroxy propyl PAB,  glyceryl PABA, p-aminobenzoic acid, padimate-O or octyl dimethyl PABA)

Cinnamates (cinoxate, ethylhexyl p-methoxycinnamate, octocrylene, octyl methoxycinnamate)

Salicylates (ethylhexyl salicylate, homosalate, octyl salicylate)

Digalloyl trioleate

Menthyl anthranilate

Avobenzone [butyl-methyoxydibenzoylmethane; Parsol 1789] - This is the only chemical sunscreen currently allowed by the European Community. However, its safety is still questionable since it easily penetrate the skin and is a strong free radical generator.

The application of retinol (normal vitamin A - also called vitamin A alcohol) or retinoic acid (vitamin A acid) may block the harmful effects of UV radiation. John Voorhees, M.D. and colleagues of the University of Michigan School reported in a series of 1998 articles published in Nature, New England Journal of Medicine, and Journal of Clinical Investigation that "Our findings suggest that applying retinoic acid or retinol to skin before going out in the sun might be beneficial... We found that ultraviolet irradiation blocks the ability of skin cells to recognize and respond to an essential nutrient called retinoic acid, which skin cells make from vitamin A or retinol. The inability to respond to retinoic acid triggers a cascade of biochemical changes that upsets the normal balance between healthy and dying skin cells. In essence, UV causes a functional vitamin A deficiency in human skin. We also found that pre-treating skin with retinoic acid---the active form of vitamin A---before UV exposure limits the extent of the harmful biochemical changes."

According to Gary J. Fisher, Ph.D., the study's co-author, UV causes a major loss of retinoic acid receptors found in human skin cells. "Retinoic acid receptors are the molecular mediators of the biological actions of vitamin A. When retinoic acid receptors are lost, it is as if the skin has no vitamin A," Fisher explained. "This is a bad situation because vitamin A is required for normal skin development and function. Retinoic acid receptors, when activated by retinoic acid, transfer genetic instructions from DNA to the cell's protein-producing factory telling it to assemble proteins needed for skin cell function.

"Eight hours after skin was exposed to UV radiation in our study, amounts of retinoic acid receptor messenger RNA and protein were as much as 70 percent lower than control levels. They remained below normal levels for more than 24 hours after exposure," Fisher said. "When skin was pre-treated with retinoic acid and then exposed to UV radiation, the amount of messenger RNA and protein still dropped, but it rebounded to normal levels within 16 hours."

Voorhees explained. "In this process, UV activates a protein complex called AP-1, which causes production of large amounts of enzymes called matrix metalloproteinases or MMPs... These MMPs break apart and degrade collagen and elastin, the major structural materials in skin. Although the broken-down collagen and elastin are replaced, the repair process is imperfect. This imperfect repair results in a tiny defect in the skin. With repeated UV exposures, the defect grows and eventually results in the wrinkled appearance of sun-damaged skin."

Voorhees and his colleagues believe the the biosynthesis and breakdown of collagen and elastin exist in a dynamic balance that is necessary to maintain healthy skin. "However, if the retinoic acid receptor pathway is disabled by UV radiation, the destructive pathway has free rein to inflict a great deal of damage," Voorhees said.

Sunlight, Skin Damage and Cancer

As indicated in the start of this chapter, the links between excessive sun exposure and cancer mortality are complex but increasing it appears that exposure to sunlight inhibits far more cancer deaths than it causes.

Sunburn and Actinic Damage

Sunburn is the most common form of skin damage caused by the sun. Pain, redness, itching, burning, blistering and peeling of the skin are the most common symptoms of sunburn. Most of the visible symptoms of sunburn begin to subside within three days.

Suntans are the result of increased pigment in the skin coupled with a mild erythema or redness to the skin. Long exposure to sunlight results in actinic skin damage such as deep wrinkling, changes in skin texture, irregular pigmentation, and loss of skin elasticity. In severe cases, actinic skin damage can result in the formation of lesions called actinic keratosis. Actinic keratosis become skin blemishes and 1 to 3% can become cancerous if left untreated to 10 to 20 years.

Skin Cancer and Other Cancers

Overall, cancer rates of the major death causing cancers are higher in sun deprived areas of the world and decrease significantly as one gets closer to the equator. In the USA, the Northern states which receive more limited amounts of sunlight have the highest rates of cancers of the breast, colon, prostate, and ovarian cancer.

Of the sun-promoted cancers, about 1 to 3% of actinic keratosis progress into cancer in 10 to 20 years. These generally are not aggressive cancers and must be left untreated for long periods of time to result in death. About 600,000 non-melanoma skin cancers occur in the USA per year resulting in about 2,200 deaths.

Malignant melanoma skin cancer is most common in people who do not receive regular sun exposure and most frequently develops on parts of the body that are not regularly exposed to the sunlight. It is the rarest form of skin cancer but is the most deadly. It affects the cells which produce melanin and seems to be more prevalent among city dwellers than among people who work outdoors such as farmers. In 1991 cancer experts estimated that there would be about 32,000 cases in the USA during the year of which 6,500 would be fatal.

Does Sunlight Exposure Increase or Decrease Cancer?

For decades, many vocal dermatologists, have held, somewhat as a quasi-religious belief, that sunlight increases the death rate from cancer. These assertions are usually supported by rather small, brief, and superficial studies (a typical dermatology study runs from one week to two months followed by a press conference). On the other hand, cancer research scientists have often come to the opposite conclusion. (It should be emphasized that most dermatologists are much more cautious and careful.)

Does Sunlight Reduce Breast, Colon, Ovarian and Prostate Cancer?

 Esther John, an epidemiologist from Northern California Cancer Center, reported in 1997 that her study shows that women who get  enough sun to make good levels of vitamin D can lower the risk of  breast cancer by 40 percent and perhaps even more.

In a study sponsored by the Department of Defense, John studied 4,881 white women, including 133 who had breast cancer. She found that women in the South have a 41 percent lower risk of dying of breast cancer, compared to cold-belt states like Michigan. Women with the lowest risk lived 20 or more years in areas with high exposure to sunlight. But as little as one hour a day of sunlight might be sufficient to improve breast cancer outcomes, she said.

The study was part of a national research project that has been following the health of about 8,000 women since 1970. The research  monitors the development of cancer and other health  events, and compares  the effects of such things as diet and exercise of women who get disease  and those who don't.

John said the study confirmed earlier findings that women who live in  the southern tier of states below Kansas tend to get breast cancer significantly less than those who live in the North.  The difference, she said, is sunlight. Southern states receive more year-round sunlight than Northern states do. As a result, people in the South get more natural ultraviolet ray exposure. John said winter sunlight is so weak in the North that people living at  or above 40 degrees north latitude do not get enough sun from November to  February to make the required levels of vitamin D. Boston is at 42 degrees latitude.

John said the study did not determine just how much sun exposure is needed to protect against breast cancer, but she said it probably is less than the amount that would cause skin damage.   "It is possible that all it takes is 10 or 15 minutes outside in bright  sunlight to get a benefit,'' she said. "But we don't really know that yet. There needs to be more study.''

In other studies, researchers at the University of California in San Diego found a close relationship  between breast cancer death rates in 87 regions around the U.S. and the amount of solar radiation calculated to be striking the ground in those cities - the higher the solar radiation, the lower the breast cancer. Gorham et al. found increased mortality rates associated with Canadian cities with the most acid haze air pollution which block UV rays. Garland et al. found the highest incidence in countries located at high latitudes.  Furst et al. reported that the there is an increased incidence associated with decreased total sunlight levels.
 

A 1994 study showed that Northern women have five times greater risk of ovarian cancer than southern women who receive more direct sun exposure. Colon cancer rates increase colon in areas with the least natural light, e.g., geographical location at high latitude (Garland and Gorham et al.). Prostate cancer mortality rates are associated with decreased UV light (Schwartz and Hulks, Hanchette).
 

Most of these studies attribute the anti-cancer effect of sunlight to increased vitamin D synthesis in the body. Sunlight is the body's only natural and reliable source of vitamin D. Studies suggest that vitamin D is linked to the prevention of breast, colon, prostate and ovarian cancers- cannot be reliably supplemented in our diet.

Skin melanoma does not appear to be a sunlight caused cancer.  A study on 4,000,000 members of the U.S. Navy followed sailors who developed skin melanoma. The results revealed a slightly higher melanoma rate, 9.5 per 100,000 as compared to the rest of the U.S. population of the same age group, 9.2 per 100,000. Sailors who worked under deck (indoor workers) showed the highest incidence of skin cancer. Sailors who worked outdoors were closest to the U.S. average. Other studies have suggested  that a lack of sunlight may increase the risk of developing melanoma, while limited sun exposure may actually decrease the risk.
 
 
 
 
 
 
 
 
 

Sunlight-inhibited Cancers

Dr. Gordon Ainsleigh in California believes that the use of sunscreens causes more cancer deaths than it prevents. He estimates that the 17% increase in breast cancer observed between 1991 and 1992 may be the result of the pervasive use of sunscreens over the past decade (Ainsleigh, H. Gordon. Beneficial effects of sun exposure on cancer mortality(Preventive Medicine, Vol. 22, February 1993, pp. 132-40). Recent studies have also shown a higher rate of melanoma among men who regularly use sunscreens and a higher rate of basal cell carcinoma among women using sunscreens (Garland, Cedric F. et al. Effect of sunscreens on UV radiation- induced enhancement of melanoma growth in mice. Journal of the National Cancer Institute, Vol. 86, No. 10, May 18, 1994, pp. 798-801).

Dr. Ainsleigh estimates that 30,000 cancer deaths in the United States could be prevented each year if people would adopt a regimen of regular, but moderate sun exposure (Ainsleigh, H. Gordon. Beneficial effects of sun exposure on cancer mortality. Preventive Medicine, Vol. 22, February 1993, pp. 132-40). Ainsleigh considers cancers (a - e) in table below as sunlight-inhibited cancer while cancer (f) is sunlight-promoted.

But what about ozone depletion and skin cancer? Professor Johan Moan of the Norwegian Cancer Institute found that the yearly incidence of melanoma in Norway had increased by 350% for men and by 440% for women during the period 1957 to 1984. He also determined that there had been no change in the ozone layer over this period of time. He concludes his report in the British Journal of Cancer by stating "Ozone depletion is not the cause of the increase in skin cancers" (Moan, J. & Dahlback, A. The relationship between skin cancers, solar radiation and ozone depletion. British Journal of Cancer, Vol. 65, No. 6, June 1992, pp. 916-21).
 
 

Cholecalciferol: the Sunlight "Vitamin"

Most of the body's cholecalciferol or vitamin D3 (commonly known as vitamin D) supply, about 75% of it, is generated by the skin's exposure to UVB rays. Anthropologists have postulated that the development of light skinned  people reflected a need for vitamin D. Humans probably arose in tropical climates since the temperature at which we are never cold nor hot is about 70 degrees Fahrenheit. As humans moved to colder and darker climates, the weaker sunlight favored reproduction of less-pigmented persons who could produce vitamin D in their skin with less light.

Using a sunscreen drastically lowers the cutaneous production of vitamin D3. A low blood level of vitamin D is known to increase the risk for the development of breast and colon cancer and may also accelerate the growth of melanoma.

Cholecalciferol itself is not biologically active. It must be hydroxylated twice for activation, the first time in the liver and the second in the kidney (in the proximal convoluted tubule). The final product 1,25-dihydroxycholecalciferol or 1,25(OH)2D is secreted into the blood for delivery to target cells, where it acts the same way as steroid hormones do: it binds to a receptor protein in the cell's nucleus, which then binds to regulatory sequences on DNA. This complex induces the transcription of RNA, which codes for proteins involved in cell function.

The primary function of vitamin D is whole-body calcium homeostasis. Along with parathyroid hormone and calcitonin, vitamin D provides the control mechanism for preventing hypocalcemia or hypercalcemia. One of the most important proteins induced by vitamin D is a calcium-binding protein in the duodenal mucosa. This protein increases calcium absorption in response to low calcium supply or increased physiologic requirements (such as growth or lactation). Vitamin D is also involved in the handling of calcium by the kidney. Thus, vitamin D is technically a steroid hormone synthesized in the kidney in response to calcium needs. There is a specific 1,25(OH)2D receptor protein found in most nucleated cells in the body. This implies that vitamin D has more functions than just calcium homeostasis (which would only require receptors in gut, bone, and kidney tissues). Vitamin D may be involved in immune function and skeletal muscle activity and may suppress cell proliferation.

Sunlight, Sexuality and Mental Health

Traditionally in spring, a young man proposed to a girl requesting she be his wife. Marriages were usually in midsummer. The couple dressed up accompanied by adults and children came to the church. Afterward in most local traditions there was feasting, drinking, and dancing into the evening. They were actually performing a ancient magical rites emphasizing the connection between sexuality and fertility in humans.

Numerous studies indicate that fertility and sex drive increase when sunlight is more intense. Testosterone levels in males are higher in the summer.  Studies at Boston State Hospital by Dr. Abraham Myerson found that ultraviolet light increased male hormone levels by 120%. Ultraviolet light also increases the level of female hormones. More children are born during the spring and more birth control devices are purchased during the summer months.

A further link between sunlight, sex drive and health is the findings that women who have frequent orgasms (with or without a partner) are much more likely to survive breast cancer. Since survival from breast cancer depends largely on whether the cancer has metastasized to other parts of the body, it looks like orgasms somehow prevent metastasis, probably by immune-system stimulation.

On the other hand, sex drive wanes in winter. A decrease in female fertility in winter has been documented beginning with North Pole explorer Admiral Byrd's observations a century ago. His expedition reported that  Eskimo women lacked menstruation, and thus ovulation, during the periods of 24 hour darkness in their winter. Also in winter, male testosterone levels drop and sperm counts are lower.

Infertility is a problem that seems to have increased in recent years. Research on light therapy has suggested that our decreased exposure to natural sunlight reduces fertility. The average office lighting is a much lower intensity than sunlight and lack the full spectrum of sunlight.

Light was first used to help infertile couples by Dr. Edmond Dewan at the renowned John Rock Reproductive Clinic in Boston (published in the American Journal of Obstetrics Gynecology, 1967). Couples were given a specially designed light to keep on while they were asleep for three nights a month. The three nights were planned to be the same three days over which ovulation was expected to take place. The couples using the light therapy had a much higher rate of conception than those not using the light.

Seasonal Affective Disorder (SAD)

An estimated 35 million Americans suffer from SAD for whom sunlight or full spectrum light therapy from November to April often improves their mental state. SAD symptoms include: limiting social contact, loss of energy, depression, decreased interest in sex, weight gain, oversleeping and withdrawal.  This usually occurs in the winter.

SAD has been successfully treated with exposure to bright artificial light of higher intensity than is usually found in the home or in the work place. Many people not suffering from SAD may nonetheless have seasonal changes which could be helped by environmental light supplementation.

Six patients with Seasonal Affective Disorder showed marked improvements in depressive symptoms after following three different two-hour schedules of bright artificial light, and they relapsed when the light was withdrawn. (Hellekson, C.J. Kline, J.A. Rosenthal, N.E. Phototherapy for Seasonal Affective Disorder in Alaska. American Journal of Psychiatry, August 1986. 143(8) p 1035-7.)

Bright light can suppress nighttime melatonin production in humans, but ordinary indoor light does not have this effect. This finding suggested that bright light may have other chronobiologic effects on humans as well. Eight patients who regularly became depressed in the winter (as day length shortens) significantly improved after 1 week of exposure to bright light in the morning (but not after 1 week of bright light in the evening). The antidepressant response to morning light was accompanied by an advance (shift to an earlier time) in the onset of nighttime melatonin production. These results suggest that timing may be critical for the antidepressant effects of bright light. (Lewy, A.J. Sack, R.L. Miller, S. Hoban, T. Antidepressant and Circadian Phase-shifting Effects of Light Reprint Series, 16 January 1987, Volume 235, p 352-4.)

Sunlight, the Pineal Gland, and the Sleep-waking Cycle

Sunlight synchronizes the circadian sleep-wake cycle by the pineal gland. The French philosopher Descartes decided that the pineal gland was the seat of the human soul, the location of what we call the mind. The pineal does contain a complete map of the visual field of the eyes, and it plays several significant roles in human functioning.

The pineal gland receives information from the eyes to regulate timekeeping for the human body. At night it secretes melatonin which, in turn, induces sleep. Melatonin has been shown to inhibit the growth and metastasis of some tumors in experimental animals, and may therefore play a role in cancer inhibition. Removal of the pineal gland and/or reduction in melatonin output have been implicated in the increased incidence of breast cancer in laboratory animals. Patients who have breast cancer have lower levels of melatonin in the blood. The hormone has also been shown to be protective against genetic damage, and it has a stimulatory effect on the immune system.

Sunlight Exposure may Reduce Schizophrenia in Newborns

Schizophrenia, in Europe and North America is most common in persons born in March. People with darker skin pigments who migrate to northern countries are 3 to 4 times more likely to develop schizophrenia than lighter-pigmented inhabitants of these countries.  Drs. John McGrath and Alan Mackey-Sim (Centre for Schizophrenia Research, Wacol, Australia and Griffin University, Brisbane, Australia) presented evidence that a lack of enough sunlight to form adequate vitamin D in pregnant mothers causes this increase in of schizophrenia. Sunlight normally converts a molecule, 7-dehydrocholesterol, into vitamin D. Vitamin D in turn increases the production of nerve growth factor that is needed in the developing brain of a child.

Further studies found that pregnant rats, that were vitamin D deprived, produced offspring with brain abnormalities and behavior abnormalities similar to those observed in humans with schizophrenia or a type of rat bred to act as a model of the disease. Dr. McGrath comments that a few minutes of standing in sunlight every day might be enough to protect a developing fetus from the disease. ("Let the sun shine in", The Economist, Feb 9, 2002, p.71)

Sunlight as a Treatment for Psoriasis

Sunlight and UV light is an effective treatment for psoriasis. Reports from the National Psoriasis Foundation indicate that 80 per cent of those suffering from this skin disease improve when they are exposed to UV light.

Natural sunlight can significantly improve, or clear, psoriasis. Regular daily doses of sunlight taken in short exposures are recommended. Avoid a sunburn which may make psoriasis worse. Be aware that it can take several weeks to see improvement. This natural approach to treating psoriasis is often referred to as climatotherapy. Some people travel to Florida, Hawaii, or the Caribbean to use swimming and natural sunlight as their psoriasis treatment. The most recognized site for climatotherapy is the Dead Sea in Israel, with treatment solariums and supervised medical assistance.

While many dermatologists admonish psoriasis patients to only use prescription tanning devices combined with photosensitizing psoralens (psoralens increase skin cancers approximately 80-fold), there is evidence that commercial tanning bed therapy is effective. In a six-week study of 20 patients with stable psoriasis vulgaris, patients received three to five tanning sessions per week in commercial tanning beds without psoralens. The ultraviolet dosage was adjusted to just be below the amount required to produce erythema (redness) of the skin. All patient demonstrated benefit from the tanning beds with the average Psoriasis Area Severity Index dropping from 7.96 to 5.04. (Reference: A. B. Fleischer et al, Commercial tanning bed treatment is an effective psoriasis treatment, J. Invest. Derm. 109:170-174, 1997.)

Special Sunlight Sensitivities

A number of drugs, photosensitizers and disease conditions increase your sensitivity to ultraviolet light. Suntanning should be avoided or used with special caution if you are in one of these categories.

Drugs include:

           1. Tetracyclines ( Declomycin Vibramycin)
           2. Thiazide Diuretics (Diuril, Hydrodiuril, Hygroton, Dyazide)
           3. Hypoglycemic agents (Antidiabetics)
           4. Sulfonamides
           5. Phenothiazines (Phenergan, Thorazine, Stelazine, Compazine )
           6. Nalidixic Acid
           7. Quinidine and Quinine
           8. Lomotil
           9. Griseofulvin
          10. Psoralens

Topical Photosensitizers include:
             1. Oil of Bergamot (perfumes, cologne)
             2. Some deodorant soaps
             3. Plants occasionally (figs, limes, celery, parsnips)

Photosensitivity Diseases include:
             1. Herpes Simplex
             2. Porphyrias (Erythropoietic Proto-porphyria, Porphyria)
             3. Discoid and Systemic Lupus Erythematosus
             4. Polymorphous Light Eruption
             5. Xeroderma Pigrnentosa
             6. Solar Urticaria
             7. Dermatomyositis
             8. Actinic Reticuloid