Sunlight Exposure

Sunlight Exposure: Overview

While it is wise to avoid burning or excess tanning from solar or indoor ultraviolet radiation, it should be realized that solar UVB radiation (290-315nm wavelength) is the primary source of vitamin D for most people.  Dietary sources are generally inadequate, and supplements have to be used carefully.

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As for melanoma and other skin cancer, a couple of points should be made.  First, while ultraviolet radiation generates free radicals that can do damage, dietary antioxidants and skin pigmentation are nature's way of fighting free radicals.  A paper by Millen et al.  reported that diets high in antioxidants and low in fats and alcohol can reduce the risk of melanoma by about 50% [Diet and melanoma in a case-control study. Cancer Epidemiol Biomarkers Prev. 2004 Jun;13(6): pp.1042-51].

Second, occupational exposure to ultraviolet radiation is associated with reduced risk of melanoma [Kennedy et al., Leiden Skin Cancer Study. The influence of painful sunburns and lifetime sun exposure on the risk of actinic keratoses, seborrheic warts, melanocytic nevi, atypical nevi, and skin cancer. J Invest Dermatol. 2003 Jun;120(6): pp. 1087-93].

Function; Why it is Recommended

Vitamin D is manufactured in the skin following direct exposure to sunlight.  The amount of vitamin D produced in the skin varies depending on time of day, season, latitude and skin pigmentation.  Usually 10-15 minutes exposure of hands, arms and face two to three times per week (depending on one's skin sensitivity) is enough to satisfy the body's vitamin D requirement.  Use of sunscreen markedly diminishes the manufacture of vitamin D in the skin, as does window glass, clothing and air pollution.  The fairer your skin color, the more vitamin D you make.  As adults age, their ability to make vitamin D through the skin decreases.  People who are housebound and experience no sunlight exposure are unable to make vitamin D.

The health benefits of UVB through production of vitamin D are considerable, with more benefits being recognized at a rapid pace.  It has been estimated that half of those with multiple sclerosis in the U.S. would not have MS if they had as much UVB exposure as those living in the southern states.


Mid-day summer sun is the best source of UVB, since minimal exposure times are required, and the UVB to UVA (315-400nm) ratio is highest.  If using sunscreen, it might be advisable to go into the sun for 10-15 minutes without sunscreen to generate a day's worth of vitamin D.

Sunlight Exposure can help with the following:



Hypertension (High Blood Pressure)

In January, 2014 the Journal of Investigative Dermatology reported that just 20-30 minutes of exposure to sunlight lowers blood pressure by about 5 points for half an hour.  The researchers, from University of Edinburgh and the University of Southampton, suggested that sunlight increases levels of nitric oxide, a chemical linked to blood flow.


Low Melatonin Level

Proper exposure to light and dark can improve melatonin production by 50-200%.  For optimum melatonin levels you need at least 30-60 minutes of outdoor light daily, preferably in the morning, and you need a very dark room at night.  Sunglasses can confuse the brain, so reducing or eliminating their use is recommended.  If you can not be outside or you live in a dark, gloomy climate, full spectrum indoor light can help.  If you cannot darken your bedroom, use a sleep mask.


Seasonal Affective Disorder (SAD)

Since the 1980s, patients have been using light therapy for the treatment of SAD either individually or under the direction of a medical practitioner.  The most commonly used and studied form of light therapy involves the use of a light box that administers bright light during a particular time of day, usually in the morning but sometimes in the evening.  More recently developed but less studied forms of light therapy include dawn light simulation and the use of light visors.  The antidepressant effects of light therapy are thought to be mediated through the eyes, not through skin exposure.

Combinations of the three components of light therapy (timing, intensity and duration) can affect the outcome of treatment.  Long-term efficacy has not been established, and the intensity-response relationship, the optimal treatment schedule, and the long-term safety of light therapy have also not been clarified.

Although there as been controversy about the importance of timing, studies have confirmed that, on average, morning light therapy is superior to evening light exposure.  The wavelength or type of light (incandescent, fluorescent) is not as important as intensity, but white light may be superior to narrow band wavelengths.  Ultraviolet wavelengths are not necessary for the antidepressant response, and should be avoided because of long term toxicity.

Light intensity is usually expressed in "lux", a unit of luminance.  As a reference, indoor lighting is usually less than 500 lux, outdoor light on a cloudy day ranges from 1,000 lux to 5,000 lux, and midday summer sunlight can reach 50,000 lux or higher.  The usual dose of light therapy used in previous studies was 2,500 lux for at least one to two hours per day, but further research showed similar benefit with 30 minutes of 10,000 lux exposure.  Since shorter periods of exposure are more convenient, the 10,000 lux fluorescent light box has become the clinical standard.

Commercial light devices are now widely available in medical supply stores or through mail order.  A light device should meet government electrical safety standards, have a filter for the ultraviolet wavelengths and have been tested in reputable clinical trials.  Patients must maintain proper distance and positioning to ensure the correct dose of light exposure.  Because of the rapid response and relapse with light therapy, patients should become involved as active participants in determining their optimal dosing of light.  For example, if patients respond to early morning light exposure, but the time is inconvenient for them, they can try shifting the exposure time to afternoon or early evening.  Alternatively, they can try to reduce the duration of exposure to 15 minutes for maintenance.

Some response to light therapy generally occurs within two to four days, and measurable improvement is often seen in one week.  Most patients experience rapid recurrence of symptoms after discontinuing light therapy.  Longer trials have shown increasing improvement after two weeks, and further gains at three or four weeks.

The common side effects of light therapy reported by patients in clinical trials include eye strain or visual disturbances (19%-27%), headache (13%-21%), agitation or feeling "wired" (6%-13%), nausea (7%), sweating (7%) and sedation (6%-7%).  These side effects are generally mild and subside with time or by reducing the dose of light.  Extreme mood shifts have also been reported as uncommon but serious side effects of light therapy.

Light therapy should be administered under the guidance of an experienced and trained medical professional to properly diagnosed patients who have no psychotic disorder and who are not suicidal.  Light therapy continues to be an investigational treatment, but with well-established benefits for users.

Panic Attacks

A study found that 9 of 22 patients had panic attacks more frequently in winter.


Problems Caused By Being Overweight

October 2014: A study by scientists at Edinburgh and Southampton universities and published in the journal Diabetes has shown that moderate sunlight exposure causes the skin to release a gas called nitric oxide, which in turn helps regulate metabolism and slow weight gain.


Osteoporosis - Osteopenia

Habits to curtail include heavy smoking, excess alcohol consumption, and limited sunshine exposure or vitamin D intake.

Organ Health

Diabetes Type II

October 2014: A study by scientists at Edinburgh and Southampton universities and published in the journal Diabetes has shown that moderate sunlight exposure causes the skin to release a gas called nitric oxide, which in turn helps control the metabolism and slow weight gain.  Rubbing a cream containing nitric oxide on to the skin can have the same effect.  The researchers commented, "Our observations indicate that the amounts of nitric oxide released from the skin may have beneficial effects not only on heart and blood vessels but also on the way our body regulates metabolism."



Summer sun is the best source of ultra-violet light, and many people find psoriasis settles very well in summer.  Treatment in winter can be aided by artificial lamps: smaller lamps are usually not strong enough, but impulse type lamps, wall mounted "fluorescent lamp type" lamps, and larger "solarium" lamps are suitable.  Unfortunately, some psoriasis sufferers are rather sensitive to sun light, and may not be improved with this treatment.

It is usually best to apply a tar or dithranol preparation daily, to be followed later by ultra-violet light treatment.

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Sunlight Exposure can help prevent the following:


Vitamin D Requirement

People should aim to get 10 to 15 minutes of exposure to direct sunlight each day when the weather allows, without sunscreen, to allow adequate synthesis of vitamin D.  Most people achieve this simply by going about their daily activities.  Those living at higher latitudes (further from the equator) should supplement their diets to ensure they are getting enough vitamin D, particularly during winter.  A lack of sun during the winter months means that many people are deficient in this vitamin by December each year.

In the spring and summer, light-skinned adults can make large amounts (20,000 IU) by sunbathing on both sides, without sunblock, for a few minutes (about one-third the time it takes for the skin to begin to slightly redden).  Darker-skinned persons need 5 to 10 times longer depending on the amount of melanin pigment in the skin.

Vitamin D production occurs within minutes and is maximized long before the skin turns red or begins to tan.  One does not have to get repeated blood tests when using sun exposure to obtain vitamin D. Toxicity cannot occur even with heavy and continuous sunbathing because ultraviolet light begins to degrade vitamin D after making about 20,000 IU, thus reaching a steady state.

Tumors, Malignant

Cancer, General

Staying out of the sun completely may increase your chances of developing cancer, say doctors.  For years, experts have advised people to cover up in the sun to protect themselves from skin cancer.  A letter in the British Medical Journal (November, 2003) from professor Cedric Garland of the University of California warns people against taking this advice to the extreme.  He says that a lack of sun can reduce levels of vitamin D, which may increase the risk of cancer.  Studies have suggested that vitamin D can protect against colon, breast, prostate and other cancers.

Ovarian Cancer

Vitamin D metabolite receptors are found on endocrine and reproductive organs and are known to play a role in inhibiting a number of cancer cell lines.  The incidence of ovarian cancer varies with latitude, with higher rates in northern parts of the world.  In this study, the quantity of sunlight was strongly inversely correlated with the incidence of death due to ovarian cancer in 100 of the largest US cities (1979-88) after adjustments were made for air pollution levels.  Northern women in the 5th decade of life were found to have 5 times the mortality rate from ovarian cancer as southern women. [Epidemiol 23 (6): pp.1133-36, 1994]

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