Sunlight, Nutrition and Health Research Center (SUNARC)

Sunlight, Nutrition And Health Research Center

Ultraviolet Radiation
Vitamin D recommendations
Vitamin D requirements during pregnancy and lactation
Why is the public misinformed about UV and vitamin D?


Cancer Mortality Maps
- Breast Cancer
- Colon Cancer
- Ovarian Cancer
- Multiple Sclerosis

About Us

Position Papers






Position of health organizations and agencies in Australia, Canada, New Zealand, the United Kingdom, and the United States, and the World Health Organization, on UV radiation and vitamin D



Questions and Comments

To whom it may concern~

I believe one of the biggest health myths is that God's sunshine is bad for our health. Thank you for spreading the truth about what so-called health experts have been telling us for years is detrimental to us.

You have a very fascinating website with interesting maps depicting mortality rates of various degenerative illnesses. Was there a study on skin cancer mortality rates and if so was there a map graphing those results?

Thank you,
M. S. T.


Thank you for your comments and question.

You may find the maps for skin cancer mortality rates at: 1. Devesa SS, Grauman DJ, Blot WJ, Pennello GA, Hoover RN, Fraumeni JF Jr. Atlas of Cancer Mortality in the United States, 1950-1994. NIH Publication No. 99-4564, 1999. (accessed April 21, 2004)

I show that 47,000 Americans die prematurely annually from 16 types of internal cancers due to insufficient vitamin D; 8,000 die annually from melanoma and 2,000 die from other skin cancer, but UV exposure is only one of a number of risk factors for skin cancer. Pale skin type, many moles, smoking, high fat, low fruit and vegetable diet, frequent sunburning, etc., are additional risk factors.

Best regards,
William Grant

Dear Dr. Grant,

I am curious about the effects of altitude on UVB exposure / availability. Does the "thinner air" at say, 5000 feet, really make a significant difference in the amount of useful UVB radiation I could absorb during sunning?

Is there a table somewhere that documents, for instance, the amount of the radiation increase per 1000 feet rise in altitude above sea level? (Or even a simple rule-of-thumb, like the aviator's "adiabatic lapse rate" rule that estimates a ~3-degree F fall in temperature for each 1000-foot rise in elevation.) For that matter, is there a way to calculate the various factors: skin color / tanning tendency, age, latitude, UV "intensity", season of the year, amount of exposed skin area, time of day, "etc", to determine an individual person's optimal exposure time for a desired daily Vitamin D dose?

Do other environmental factors, such as relative humidity, play any role in how much radiation exposure you can expect? I know that clouds can be a factor (I'm not sure how to quantify them, though). Is it as simple as "50% cloud cover reduces exposure by 50% over a clear sky's rate", regardless of altitude / latitude?

Is there any evidence that a body with a low 25-hydroxyvitamin D (25(OH)D) level is in any way "thirstier" for sun exposure, or that it absorbs / converts sunlight more readily (given the opportunity) than one which is already at a higher / healthier level?

Are there any skin preparations (such as slathering yourself with coconut oil, perhaps) that enhance / facilitate absorption?

Thank you for your informative site, and for your time in considering these questions!

CB in Reno, NV

Thanks for your interesting questions.

Yes, the altitude at which one is exposed to UV radiation strongly affects the UV dose. Reaching back to my atmospheric science days at NASA, I recall a paper by Blumthaler et al [1994] in which this question was addressed. They placed two spectroradiometers (instruments with a grating so it can measure the variation in irradiance with wavelength) at 2 locations in the German alps separated by 1 km in elevation. For the DNA-weighted UVB spectral distribution, which is very similar to the vitamin D-production spectrum, they obtained a model result of 21% increase/km in a continental atmosphere and 23%/km in an urban atmosphere. For the erythemal (sunburning) action spectrum, they obtained a model result of 16%/km for a continental atmosphere and 18%/km for an urban atmosphere. The erythemal result is slightly lower than the DNA result because atmospheric scattering increases as the inverse fourth power of wavelength and ozone in the troposphere also absorbs UVB (290-315 nm) but not UVA (315-400 nm). 5,000 ft. is about 1.5 km, so there is about 35% more UVB at that altitude than at sea level. The higher surface elevation of most states west of the Rocky Mountains is one reason why UVB is higher and mortality from internal cancers is lower than east of the Rockies (see the maps at A second reason is that the column ozone is lower west of the Rockies since the prevailing westerly winds have to push over the Rockies and, in doing so, push up the tropopause and make for a thinner stratosphere. A third reason is that more people live in urban areas in the east and, as a result, spend more time indoors.

Water vapor in the atmosphere would have little effect on UVR reaching the surface unless the humidity rises above 70% or so and aerosols increase in diameter, at which point they absorb or scatter more UVR. However, much of the scatter still reaches the surface, so the effect is rather small. Clouds do attenuate UVR to some extent, but I think it is still possible to sunburn on a cloudy day.

I don't think that the body makes vitamin D at a faster rate when 25(OH)D levels are low. On the other hand, UVA will destroy vitamin D, so the full solar UV spectrum helps keep vitamin D at proper levels.

As for enhancing vitamin D production, I think the more important consideration is reducing the effect of free radicals generated in UVR. It is important to have either a diet high in fruits and vegetables or supplement with antioxidants such as vitamins C and E. In addition, beta carotene, found in carrots for example, is considered "nature's sunscreen" and can reduce the penetration of UVR in the skin. However, large doses can lead to prooxidant effects.

Check PubMed ( for papers on the topic.

William Grant

Blumthaler M, Webb AR, Seckmeyer G, Bais AF, Huber M, Mayer B. Simultaneous spectroradiometry: a study of solar UV irradiance at two altitudes. Geophys. Res. Lett., 1994;21:2805-2808.


I am having a hard time finding information on the beneficial effects of sun bathing. I keep hearing that the sun ages the skin prematurely. Is this true? I have very fair skin and live in Florida. I've always worn sunscreen and never felt well while out in the sun. Recently, I stopped the sunscreen use after hearing that we need the sun, and now when I am outside I don't feel uncomfortorable as I did while wearing sunscreen everyday.

My question is how to prevent photo aging? Could the sun cause skin aging only under certain circumstances such as low antioxidant intake. Could topical antioxidants protect the skin from aging while in the sun? I don't want to become sick from lack of sunlight, but I also don't want to have skin damage and wrinkles from the sun. Any advice on this?


Dear K.,

Thanks for your question.

Since you have fair skin, you are correct to be concerned about spending too much time in the sun in Florida. You skin is adapted for living around 50 deg. N; you now live near 30 deg. N. The appropriate skin color for Florida is olive, such as in Japan, the Mediterranean, or the Middle East. The important things to do in your condition are the following: 1 - avoid reddening or burning; 2 - avoid excess tanning; 3 - think about natural ways to prevent damage from or counter the effects of solar UV radiation. UVB radiation (290-315 nm) generates vitamin D in the skin, but, unfortunately, is the primary spectral region blocked by sunscreen. Vitamin D has been shown to affect mood positively. That may be the reason you feel better in the sun when not wearing sunscreen. In addition, melanin is nature's way of protecting against UV radiation, produced either genetically or through tanning. Melanin both blocks the penetration of UVB as well as repairs some of the damage done by UV.

I presume you don't smoke, eat lots of certain types of fat, and are not overweight - each of these also contribute to adverse effects from UV exposure.

The other thing you can think about doing is consume fruits, vegetables, and dietary supplements to block the UV radiation and combat the free radicals generated by the UV. Carrots have beta carotene which is considered by some to be Nature's sunscreen. It goes to the skin and can color it orange or yellow, and absorbs UV radiation. In addition, carotenoids, tocopherols (vitamin E), ascorbate flavonoids, and n-3 fatty acids are also very useful in combating free radicals. This recent paper by Sies and Stahl is an excellent review of the topic. If you ask the authors for a copy, I think they will send you one.

Nutritional Protection Against Skin Damage from Sunlight, Annual Reviews of Nutrition,
Sies H, Stahl W,
Institut fur Biochemie und Molekularbiologie I, Heinrich-Heine-Universitat Dusseldorf, PO Box 101007, D-40001
Dusseldorf, Germany.

You might also visit and do a literature search on topical application of vitamins C and E for combating the free radicals developed from UV exposure. I think that there are some interesting results and that it is effective.

One other thing to consider is that lipids in the skin probably also provide protection against UV radiation. Unfortunately, soaps tend to pull these lipids out of the skin, and it can take up to a week to replenish them. You might consider not washing with soap during the sunny season in Florida.

I plan to write an essay on the topic you raise and post it at in the near future. I'd be interested in your comments and what you find if and when you follow any of these suggestions.

Best regards,
William Grant

Thank you for your work in Vitamin D research.

My husband and I live in Iowa. We are ages 53 and 50. We just learned that we both are extremely deficient in Vitamin D. I have also learned I have osteoporosis. My husband is due for a bone scan soon, and I won't be surprised to learn if he has it too. He has had Crohn's Disease for 30 years, and has had three bowel resections over the years, and suffers from malnourishment.

We just purchased the Sperti tanning lamp, with stand. My question is: how much exposure do we need to get our Vitamin D levels up and to maintain them? Is 10 min. a day or every other day enough? Can it be 5 minutes on two different areas, or does it have to be 10 min. on one area?

Exposure times and schedules are dependant upon the skin type of the person using these products. Persons with Skin Type I, those who do not tan at all and most always burn, should limit their exposure to around 1 minute, or up to the point where the skin begins feeling tingly, but no longer. Skin Types II, III, and IV (increasing pigmentation) should follow the stated exposure schedules listed on the machine or lamp. One of the advantages of obtaining vitamin D from ultraviolet B (UVB) radiation is that it is difficult to produce too much vitamin D since the UVB also destroys vitamin D in the skin. The only sure way to determine whether you are obtaining adequate amounts of vitamin D from all sources is to have your serum 25-hydroxyvitamin D (25(OH)D) level measured. The test can be ordered by an MD or nutritionist.

The heavy UVA component of tanning lamps is a concern, but probably not as much for seniors in the realm of photoaging and skin cancer as for younger people. As with all things, moderation and perseverance should be advised.

Also, which months in Iowa can we get Vitamin D from the sun???

For Boston (42.3 deg. N), one cannot obtain vitamin D from the sun for the 4 darkest months of the year. Thus, for Ames (42 deg. N), the result would be about the same.

I was shocked to learn of my Vitamin D deficiency, since it is added to milk, orange juice, and in my multiple vitamin.

Thank you for your help.
M. S.
Ames, Iowa

Current scientific indications indicate that about 1000 I.U. per day of vitamin D is required for optimal health, although the amount will vary with age, body mass index, etc. It is unlikely that milk, orange juice, and a multiple vitamin will provide 1000 I.U. per day. In addition, those with Crohn's disease suffer from impaired ability to absorb nutrients including vitamin D, so in that case, exposure to UVB radiation is the preferred way to obtain vitamin D.

Thank you for your questions.

Best regards,
William Grant

I appreciate your response.

This research is extremely interesting and important. I will pass along your website to our physician. It is interesting that we had never been tested for our vitamin D levels until this past winter. I will be getting another test soon to see if I've made any progress. I've been taking two tsp. cod liver oil daily, plus the recent addition of the Sperti lamp.

M. S.
Ames, Iowa

I recently read an interview with William B. Grant on the Mercola Website

There is the following quote: ". . . because when adding 'vitamin' D to foods in the early years to prevent bone problems (in the UK and later in the U.S.) there were many problems of excess, so much so that deaths occurred."

That quote is from Oliver Gillie: "In the United States, for example, almost all milk is fortified with vitamin D. In France milk fortified with vitamin D is available as a choice. Such milk is not available in the UK because all fortification stopped following a scare about the effects of such milk on babies in the 1950s (which was due to doses much too high)." You may reach him at "Oliver Gillie" after April 15. He lives and works in London.

I am curious what evidence there is for these deaths? I'm going to include a number of quotes from reading I have done of interviews or papers by John Jacob Cannell -- in particular he makes reference to the work of R. Vieth, which seems to indicate that it is nearly impossible to kill yourself from Vitamin D overdose.

I think it is an important issue. I am very concerned about health because of personal illness and have probably been deficient in Vitamin D for years. It is of some concern to me to find competing "experts" that recommend vitamin D but have such differing ideas about how much (Grant recommends 1,000 units a day, Cannell quotes a paper by Heaney that says we use between 3,000 & 5,000 units a day).

Oakland, California

Regarding the recommended amounts of vitamin D, each individual responds differently to sunlight, food, and supplemental vitamin D. Excess vitamin D can lead to reduction of bone mass and increased risk for prostate cancer [Tuohimaa et al., 2004; Grant, in press]. The best way to determine what is right for each individual is by having accurate serum 25(OH)D levels measured. A doctor or nutritionist can order the test.

Best regards,
William Grant

Dear Dr. Grant,

I would appreciate your enlightening me in the area of D toxicity. I have several patients (I am a dentist) who have dramatically resolved with D2 50,000 IU every other day. (Ostoforte) The most dramatic case is that of a 35 age lady for whom it was impossible to do an exam, because she could not keep her mouth open for more that 5 seconds without going into intense spasm pain. She had deep caries in several teeth. One week after D2 50,000 IU daily, she was able to keep her mouth fully open for an hour while I did restorations. Same thing a week later. I tried to reduce the D2 to one weekly, but this didn't work. She is currently maintained on 1 capsule every 2'nd day. I have read on the net that D2 is a nontoxic form of D, and this is backed up by research at Univ. of Chicago, by two Ph.D.'s and an MD. This info I gleaned from Robert Barefoot's book "The Calcium Factor." Krispin Sullivan has informed me that Barefoot is wrong.

I am aware of the downside of too much D, but which form? D2 or D3? I do not wish to endanger patients with excess D, but they are in agony without Ostoforte , and have tried everything else, (bite plains, etc.) Would appreciate your commenting.

G. P.
Corner Brook, Newfoundland

Dear G.P.,

Your question is a bit out of my area of study, but I did do a quick search at PubMed ( and found this paper:

Ugeskr Laeger. 2000 Nov 13;162(46):6196-9. [Vitamin D deficiency among immigrants] [Article in Danish] Glerup H. Medicinsk afdeling C, Arhus Universitetshospital, Arhus Amtssygehus.

Vitamin D deficiency in immigrants has been known in the UK for 30-40 years. In Denmark, we have become aware of the problem only recently. Of 69 randomly chosen Palestinian women living in Denmark 85% were found to have very low levels of 25-hydroxyvitamin D (< 10 nmol/l). Vitamin D deficiency is caused by inadequate exposure to sunlight and a low dietary content of vitamin D and calcium. Typical symptoms are muscle pain, muscle spasms, diminished muscular strength, deep bone pain, and paraesthesias. The diagnosis can be tested by three blood tests: serum 25-hydroxyvitamin D, serum PTH, and serum alkaline phosphatase. If a combination of low 25-hydroxyvitamin D and secondary hyperparathyroidism is found, the treatment should be high-dose ergocalciferol or cholecalciferol (100,000 IU weekly). If only (isolated) low 25-hydroxyvitamin D is found, treatment with 1000 IU of ergocalciferol or cholecalciferol in combination with one gram of calcium daily will be adequate.

It supports your protocol.

Vitamin D2 is much less well absorbed than is vitamin D3, but I don't have information on the differences. I would suggest that you consider having your patient's serum 25(OH)D levels checked, and then recommend that she take steps to increase her serum 25(OH)D levels through natural or artificial ultraviolet-B (UVB) exposure and vitamin D3 supplements at lower amounts, then have her serum 25(OH)D levels re-tested in a month or two. However, since you are in Newfoundland, solar UVB levels are likely to be too low for vitamin D production about half the year.

Best regards,
William Grant

Dr. Grant,

I found your excellent article in Dr. Mercola's newsletter. While exposure to the sun is recommended, I haven't seen any real emphasis on the effects of the presence of sun blockers in virtually all cosmetic products on the market for women. This fact dawned on me when I realized that even my all natural powder foundation has a sun block.

I have read somewhere that going from your car to home, etc. could be enough sun exposure. But how many women are under the false impression that they are producing Vit. D by being in the sun for limited periods and not realizing that even their hand lotion has a blocker in it? (Not to mention clothing with sun blocks.) I was one for awhile and I should know better. I have also read about the link between low levels of Vit. D and depression. Again, how many women are unknowingly blocking the sun with their make-up and becoming depressed? No allopathic doctor is likely to recognize that link.

I have been thinking about this topic for months and I am happy to know someone like yourself is getting the word out.

Thank you,
K. J., MN, RN

Dear K.J.,

Thank you for your interest in my article and your kind words. I will do what I can to increase both public and health care knowledge of the importance of vitamin D from sunlight and other sources for optimal health.

Best regards,
William Grant