Vitamin D and sunlight

Why we are deficient in vitamin D

Problems caused by vitamin D deficiency

How much vitamin D do you need?

Sunlight and vitamin D

Ultraviolet radiation and vitamin D

Food sources of vitamin D

Vitamin D toxicity


Why we are deficient in vitamin D

Getting sufficient vitamin D is one of the keys to staying healthy and long-lived. Hundreds of studies show that most people in the Western world are deficient in vitamin D. Even the most conventional journals now acknowledge that a lack of vitamin D in the population is responsible for a wide variety of ailments (1, 2), as listed below.

Humans evolved in equatorial Africa, where there is constant and regular sun throughout the year. With all that sunlight, the black skin of our African ancestors synthesised much higher levels of vitamin D than most humans obtain today. About 50,000 years ago a single mutation that occurred was responsible for the appearance of white skin in humans. White skin, with less melanin, synthesizes vitamin D in sunlight six times faster than dark skin (3,14,15). These humans were able to successfully migrate to higher latitudes around the world because they could synthesise sufficient vitamin D to survive in the lower levels of sunlight there.

The majority of the world's population now lives above latitude 35 North. Most people are unable to synthesise vitamin D from sunlight for some of the winter months, depending on the angle of the sun and the amount of skin exposure they get. For example, in Seattle (47 N) and London (52 N), there is insufficient sun for skin to make vitamin D from October to April. People living at high latitudes have an increased risk of diseases caused by a lack of vitamin D (8,9,14,15).

The half-life of vitamin D circulating in the body is approximately one month. By the end of winter in the high latitudes most people are seriously deficient in vitamin D unless they have a vitamin-rich diet.

Problems caused by vitamin D deficiency

Insufficient vitamin D is associated with a wide range of modern degenerative diseases. It is absolutely essential for good health.

How much vitamin D do you need?

The level of vitamin D needed for good health is a lot higher than the U.S. Food and Nutrition Board set as the Recommended Dietary Allowance (RDA). The RDA recommends 200 international units (IU) per day for children and adults less than 50 years old, 400 IU for adults age 50-70, and 800 IU for adults over the age of 70. The RDA was set at a level that prevents rickets but does not prevent numerous other diseases.

An optimal level of vitamin D can prevent and heal cancers (4), multiple sclerosis (5), cardiovascular disease, autoimmune diseases, and infections such as influenza (6, 7). Here is the most recent thinking on blood vitamin D levels:

           ng/ml   nmol/L
           <10   <25   severely deficient
           10-19   25-49   deficient
           20-29   50-74   insufficient for good health
           30-49   75-124   sufficient for good health
           50-99   125-249   optimal for good health, healing and disease prevention
           100-150   250-375   excessive
           >150   >375   potentially toxic

Without sun exposure, the optimal level of vitamin D of 50-99 ng/ml requires 5,000 IU per day in food or as a supplement. Most multivitamin tablets contain only 400 IU of vitamin D, which is clearly insufficient.

Sunlight and vitamin D

A light-skinned adult human will synthesise 5,000 IU of vitamin D in 5 minutes of naked sunbathing at midday on the equator. Five minutes per day is all this person needs to get his/her optimal daily supply. In a little over half an hour, they'll get their entire week's optimal health allowance (assuming they get no vitamin D from their food, which is unlikely).

As you move further from the equator, further from mid-summer, further from midday, or in cloudy or polluted air, less vitamin D will be synthesised by your skin. However, at a temperate latitude with a few more minutes per day it is still easy to get your full vitamin D requirement just from the sun.

A black-skinned person will only synthesise one sixth as much as a white-skinned person. Dark-skinned people are much more at risk of vitamin D deficiency at temperate and cooler latitudes (3,15).

In my ebook Grow Youthful, I strongly recommend getting sufficient sunlight. Sunlight has many beneficial effects in addition to creating vitamin D. The light regulates sleep cycles and helps create melatonin, and the far infrared warms the body and helps with other body systems. Ultra violet rays release the nitric oxide stored in compounds in your skin, dilating blood vessels and promoting cardiovascular health. (16)

Ultraviolet radiation and vitamin D

Sunlight hitting the earth has two main types of ultraviolet radiation: A and B. High frequency ultraviolet-C radiation is generally unable to penetrate through the atmosphere.

Ultraviolet-A radiation is of a lower frequency, in the range of 400-315 nm. UV-A is easily able to penetrate the atmosphere, including clouds and polluted air. It can even pass through glass.

UV-A penetrate through the outer human skin deep down to the elanocytes, the cells that become cancerous in melanoma cases. UV-A is the dangerous ultraviolet radiation, which does its damage even on cloudy days, or if you are behind a glass window such as when you are driving. It is easy to get severely burned through over-exposure to the sun in cloudy weather. Most sunscreens do not block UV-A.

Ultraviolet-B radiation is of a mid frequency, in the range of 315-280 nm. UV-B cannot penetrate glass, and is easily blocked by sunscreens. It is partially blocked by cloud, dust, air pollution and the atmosphere in general. It gets through best in the middle of a clear day, when the sun is immediately overhead. UV-B does not penetrate the skin deeply.

It only acts on the surface of the skin, causing sunburn if you get too much of it. Sunburn is a valuable and important signal. It is your body telling you that you have had too much sun, and damage is occurring. One of the (many) reasons I don't use sunscreensis that they hide this essential signal. Even a little redness or burning causes skin damage, wrinkles, skin ageing, keratoses, skin cancers and the risk that cancers will proliferate, take hold, and metastise. (14)

UV-B is the light that helps your skin make vitamin D.

The best time of day to sunbathe is in the middle of the day when the sun is directly overhead. Beneficial UV-B exposure is maximised, making maximum vitamin D. Expose as much skin as possible for just a few minutes (longer if you are dark-skinned). Take care not do burn or go red.

In contrast, when the sun is low on the horizon, or when the sun's rays are weak, blocked by cloud or atmospheric pollution, the beneficial UV-B rays are filtered out and relatively more of the dangerous UV-A rays get through.

When you sunbathe, vitamin D is created by the action of the light on cholesterol close to the skin surface. For good health, you need sufficient cholesterol in your diet. It is one of the reasons why coconut oil, a saturated fat, is an excellent sunbathing oil. The newly created vitamin D on the oily skin surface needs 48 hours to be absorbed. Do not wash off the oil for 48 hours after sunbathing. If you have a shower after sunbathing, do not wash all your skin with soap, or you will wash away the newly synthesised vitamin D. In my ebook Grow Youthful, I suggest that you do not use soap for washing unless it is the only way to get off grime or a smell.

It is almost impossible to overdose on vitamin D from sunlight, as the body stops making it as its level approaches sufficiency.

Vitamin D from sunlight is generally more effective in health maintenance, and stays in the body about twice as long as vitamin D from food and supplements.

Food sources of vitamin D

The best food sources of vitamin D are wild (not farmed) oily fish like salmon, mackerel, and sardines and cod liver oil. Other sources include free-range eggs and free-range meat, and fresh or sun-dried mushrooms. Very little vitamin D is naturally present in our food, especially for those who consume a modern, processed food diet or people who avoid animal-based foods.

Supplement D2 or D3?

There are two kinds of vitamin D supplements: vitamin D3 (cholecalciferol), the kind our skin makes, and vitamin D2 (ergocalciferol), an inferior synthetic variant. Vitamin D2 is only 10-30% as effective in raising 25-hydroxyvitamin D blood levels compared to vitamin D3. A recent study concluded the "Vitamin D2 should not be regarded as a nutrient suitable for supplementation or fortification" (10).

Some research shows that synthetic, supplemented vitamin D may be harmful.

Vitamin D toxicity

You can take a daily 10,000 IU vitamin D supplement for many months with no evidence of adverse effect (11).

Daily consumption of 50,000 IU for several months will cause hypercalcemia (elevated calcium level in the blood), which is the first manifestation of vitamin D toxicity. In contrast, the optimal level of 5,000 IU per day prevents the build up of calcium in blood vessels (12).

In spite of the above, I would still prefer to get my vitamin D from sunlight (and from my food) rather than as a supplement. Throughout Grow Youthful I emphasise that pills and supplements are not harmless, and usually have unforeseen, often distant consequences.


1. American Journal of Public Health 2006;96:252-261

2. New England Journal of Medicine 2007;357:266-281

3. Science 2005;310:1782-1786

4. American Journal of Clinical Nutrition 2007;85:1568-1591

5. Neurology 2007;69:381-388

6. Science 2006;311:1770-1773

7. Epidemiology Infection 2006;134:1129-1140

8. Toxicology 2002;181-182:71-78

9. European Journal of Clinical Nutrition 2004;58:1095-1109

10. American Journal of Clinical Nutrition 2006;84:694-697

11. American Journal of Clinical Nutrition 1999;69:842-856

12. Circulation 1997;96:1755-1760

13. Sanders K. M. et al. Annual high-dose oral vitamin D and falls and fractures in older women: a randomised controlled trial. Journal of American Medical Association 303, no. 18 (2010): 1815-22.

14. Wang T. J. et al. Common genetic determinants of vitamin D insufficiency: a genome-wide association study. Lancet 376, no. 9736 (17 July 2010): 180-88. Epub 10 June 2010.

15. Jablonski N.G., Chaplin G. Colloquium Paper: Human skin pigmentation as an adaptation to UV radiation. Proceedings of the National Academy of Sciences 107, Suppl. 2 (May 11, 2010): 8962-68.

16. On-going research by dermatologist Richard Weller. January 2013.

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