Kurt G. Harris MD

The PāNu approach to nutrition is grounded on clinical medicine and basic sciences disciplined by knowledge of evolutionary biology and paleoanthropology. The best evidence from multiple disciplines supports eating an animal-based diet high in fat, low in cereal grains and relatively low in carbohydrate.

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How much sun?

Prompted by a reader question, here are some brief thoughts on how to get your Vitamin D the natural way.

I have seen old photos of native americans and Inuit - some of them look pretty wrinkly. I have seen photos of very old black africans and some darker skinned asians (Thai) who have skin that looks very smooth despite their age and lots of sun exposure. I have seen images of caucasian surfers in California and Hawaii who are deeply tanned but look pretty wrinkle free for their age. The most wrinkled people I see where I live get little sun and eat the SAD.

There are certainly genetic factors, including skin type.

I am doing some speculation with an evolutionary bias here, but here is my working hypothesis.

If you are a light skinned white, your melanin is low specifically to allow you to gather UVB to create D. It is not logical that this trait evolved and came with the side effect that the amount of sun required to maximize your D exposure also ruins your skin. I think that PUFAs and inadequate immune and cellular repair mechanisms and smoking themselves create skin damage and potentiate any UV damage that occurs. I think any person should be able to tolerate whole body sun exposure up to the point right before burning, whether that is 15 minutes or 8 hours depends on skin type. This will also be the amount that optimizes vitamin D.

If you are white and you go hours beyond burning every day, you may be damaging your skin beyond repair capacity and may hence be causing premature aging.

If you are black and only get 20 minutes a day you will cause no damage but will be D deficient.

So, a white person with type 3 skin, proper diet and spending an hour a day in the nothern sun in summer - no premature aging - plenty of D (If levels are low, could probably tolerate more sun)

Same person living in san diego and gettiing 6 hours a day surfing - maybe some sun damage - more than smoking or PUFAs ? I don't know.

Black skin in the north - naked all day with no premature damage -may still not get enough D

Black skin at the equator -no problem with plenty of D

Any dermatology study you read the subjects will be on the SAD. My minimal erythemal dose has at least doubled (not counting the tanning) since eliminating excess O6s.

Bottom line to my hypothesis: tolerable sun exposure for your skin type should be roughly the same as what optimizes your Vit D levels. Beyond that may age your skin prematurely.

Reader Comments (23)

What makes you state that individuals with low vit D levels "could probably tolerate more sun"?

My experience after supplementing with D3 last winter has been the exact opposite - I tan faster and have not been burnt once, which is a first for me.

August 19, 2009 | Unregistered CommenterErik

Thanks for this post Kurt, it is a question I have been pondering since your Vitamin D post and especially recently as I am leaving for a 7 day vacation in Jamaica on Friday. I will no doubt spend more time in the sun than the recommended "whole body sun exposure up to the point right before burning" while on vacation. So my question is this: Is there harm in using sunscreen? It's certainly not a natural-occurring substance that paleolithic man would slather over his body. Also, there was a chart in a presentation on Nikoley's blog implying a correlation between sunscreen sales and skin cancer in Connecticut that gave me pause...


I would appreciate your thoughts on sunscreen use following the recommended "up to the point before burning"...

Thank you, and great blog!

August 19, 2009 | Unregistered CommenterJM


The context of the essay is that if your are trying to get D from the sun, and you have your levels tested and they are low, that means you could probably safely increase your sun exposure because that is good evidence you are not getting too much.

I am not claiming anything at all re: effects of oral D3 on sun tolerance.


Hats and long sleeved shirts assure that you are attenuating UVA and UVB equally. ZInc Oxide is fine too.
Reactive chemical sunscreens actually work by creating free radicals on your skin. No proof that's bad but it doesn't sound good. They also usually attenuate UVB more reliably than UVA. I see no upside to potential sun damage without Vit D benefits.

August 19, 2009 | Registered CommenterKurt G. Harris MD

JM said:

"Also, there was a chart in a presentation on Nikoley's blog implying a correlation between sunscreen sales and skin cancer in Connecticut that gave me pause..."

I know this was directed at Kurt, but I can't resist commenting.

This effect is not restricted only to Connecticut; the same thing is happening all over the world. Sunscreen use has gone up, but melanoma has not gone down -- in fact, it's gone up. That's because they're comparing people who don't use sunscreen (and therefore get lots of vitamin D) and people who use sunscreen (and are vitamin D deficient).

I bet if they compared those who use sunscreen and take vitamin D supplements and those who use sunscreen but don't take vitamin D, there'd be a big difference in melanoma rates.

Therefore, how I see it is that if you're going to use sunscreen, remember to take enough vitamin D3.


August 20, 2009 | Unregistered CommenterJLL

coconut oil for sunscreen?

August 20, 2009 | Unregistered Commenterwes


There has been speculation about sunscreen use contributing to skin cancers as well as the various organ cancers. If you block UVB and allow UVA that may be the case.

My own back of the envelope calculation is that even if you had melanoma risk from the sun equivalent to parts of australia under the ozone hole, getting vitamin D from the sun decreases your overall risk of cancer more than an order of magnitude more than it increases your risk of death from melanoma. Melanoma risk as high as 1 in 1000 vs lifetime risk of cancer 400 in 1000. Of course, only some melanoma types are sun -related (epidemiologically)

I may post more on skin cancer in the future

August 20, 2009 | Unregistered CommenterKurt G. Harris MD


I have seen claims but it does not make sense to me that coconut oil would provide any protection at all.

I found no information on pubmed

Will make you smell good, though

August 20, 2009 | Unregistered CommenterKurt G. Harris MD


I can't help but point out here that your statement of, "It is not logical that this trait evolved and came with the side effect that the amount of sun required to maximize your D exposure also ruins your skin," has some faulty logic itself, because evolution doesn't consider disadvanagous mutations past reproductive age, as would be the case with cumulative sun damage. Also, I'm not exactly sure that the threshold of sun damage needed to produce wrinkled skin is as high as the amount needed to result in skin cancer (genetic predisposition aside).

August 20, 2009 | Unregistered CommenterNicole


Maybe I can make my logic seem less faulty to you.

This is merely a working hypothesis, but think carefully about the mechanism. We evolved to be more sensitive to UV at higher latitudes, right? I am only arguing that it is biologically plausible that the increased sensitivity to UV creating Vit D roughly paralells any increased sensitivity to sun damage.

Less time in sun required to get your dose of D, less time you can tolerate sun, but roughly parallel. It would be unlikely that the two sensitivities would suddenly become uncoupled, is all I am saying. We have already agreed that they are selected for.

Separately, I am fairly well versed in evolutionary theory. Evolution doesn't "consider" anything. It is a process and can be due to many forces besides selection. The argument that no trait that helps us survive past reproductive age can be selected for completely ignores the survival value to the family/tribe or other social unit conferred by fitness beyond reproductive age.

Humans take decades to mature and how will they survive if mom and dad drop dead shortly after birth? That argument (survival after reproductive age can't be selected for) is often heard but I do not think it is correct.

As far as thresholds for skin cancer vs sun damage, who knows? It would seem reasonable that it takes more sun to get skin cancer, but if the cancer is due to promotion by a screwed up immune system (T cells, etc) maybe not. I think skin cancer is influenced by the same things that influence other cancers. UV is an initiator, not a promoter.

August 20, 2009 | Unregistered CommenterKurt G. Harris MD


I guess my point of contention is that the trait maximizing vitamin D production could very well have evolved with the side effect of ruining your skin, because the immediate benefits of vitamin D outweigh the more long term detriments to your skin.

OR vitamin D production came after as a means to not get depressed about your wrinkles. :) (ha-ha).

August 20, 2009 | Unregistered CommenterNicole

How do we know that skin wrinkles equals skin damage ? It is surely our aesthetic view of skin that wrinkles mean something bad ?


August 20, 2009 | Unregistered CommenterAnne


That is almost exactly what I am arguing -that they are basically the same trait. The optimal time required to get D and the time you can tolerate sun without damage are linearly related. The ablity to tolerate tropical sun declined with the decrease in melanin as the ability to get D from less sun exposure increased.

So it would be unlikely that if 20 minutes of sun maximizes D that 20 minutes causes significant sun damage, and if it takes you 8 hours to get your D that is also unlikely to cause permanent damage. That was why I said it makes sense that if you take a certain length of time to get your D, it would be unlikely that that amount would also prematurely age your skin. They should both related to melanin.

Maybe re-read what I originally wrote and it will finally make sense.


You raise a very good point. There are different types of wrinkles, I am sure. Some are dermal and some are epidermal, some may be related to skin elasticity or redundancy independent of damage, but related to aging, Some may be due to oxidative damage but not sun. Look at the face of a long term smoker and see fine microwrinkes that are quite distinct from the coarser wrinkles you see with aging and are seen in those who get little sun.

August 20, 2009 | Registered CommenterKurt G. Harris MD

One question about Vitamin D and sun exposure I haven't gotten answered is how long a "dose" of sunlight --> Vitamin D lasts. Do we accumulate a reserve? There would seem to be a limit on the reserve, but is it body-fat related (IIRC, D is fat-soluble)?

Any pointers on that would be appreciated.

August 24, 2009 | Unregistered CommenterAnnlee


Any particular day of sun or oral dose of D is adding incrementally to your body stores if the dose is high enough. Think of stopping at the gas station every morning. If you get the same amount of gas you burn during the day, you are just staying even. If you burn a gallon a day and fill up with three, you will fill your tank at the rate of 2 gal per day until your tank is full. Once your tank is full, if you keep adding 3 gal and using only one per day, the rest will spill out on the ground. Your tank only holds so much. (WIth D, your tank is probably overflowing once you are at 120 or so ng/dl.)

Once it is winter the gas station is closed and your tank will deplete at 1 gal per day until you can buy gas again. It is not a particular day's gas being burnt, but what was in your storage tank, whether it came from sun or in pill form.

With your body's D stores, you are doing the same thing. Any excess for the day goes to storage. Whatever you have in storage is drawn down by the same amount that would be required to keep you at equilibrium, unless you get the equilibrium amount that day. The half life from a study on submariners is about 2 months. So if you stop getting D all of a sudden, in 2 months your stores and hence serum level of 25 OH D will be half as much. Start at 60 ng/dl, and 2 months later you are at 30, then 2 months later at 15, unless you get it in your diet or from the sun/

Mathematically it is not as linear as this simple metaphor, but I think this is a good first order approximation.

The higher your level currently, the bigger dose it will take to keep your tank full ( bigger tank but bigger burn rate as well, using our gas tank metaphor) and the more it will take to add to your stores. So it may take only 1000 units per day to get to from 20 to 30 ng/dl but it may take 4000/day to go from 30 to 40 (for example). People can vary in their metabolism so that is why it is best to get your 25 OH D measured.

(constant half life implies a 1st order differential equation, I am not sure if anyone has proved the dynamics work that way)

August 24, 2009 | Unregistered CommenterKGH

It's stored in adipose tissue

August 24, 2009 | Unregistered CommenterKGH


I'd agree -- I see levels increase or go down but usually there is a reason -- season, stress, infection, URI, (more wheat GLUTEN in the diet suddenly). This is really truly another great entry and adds to the first of the vitamin D series...

Vitamin D cured my asthma and my kids -- we were all on inhalers the last few years. The steroids in the inhalers in facted 'stunted' my kids' growth for several months whenever we had to give it to them for 1-2 mos. Now we are all COMPLETELY off inhalers and never require them. My daughter NEVER has albuterol treatments or pred tapers anymore.

One of many hormones that are important for vitality and optimal health, vitamin D is one of the most awesome. Thanks for all your great and informative posts!!


August 25, 2009 | Unregistered Commenterg

"You raise a very good point. There are different types of wrinkles, I am sure. Some are dermal and some are epidermal, some may be related to skin elasticity or redundancy independent of damage, but related to aging."

That's an interesting idea, but if loss of elasticity does not count as skin damage, then what does? The fact that young people have better skin repair mechanisms (e.g. collagen production) and less wrinkles, and old people have worse skin repair mechanisms and more wrinkles, is a pretty good indicator that wrinkles are a sign of damage.

August 25, 2009 | Unregistered CommenterJLL


I mean exposure to external agents as "damage".

Is the cause of wrinkles with aging "damage" or the age related failure to keep up with it?

The point is that you will get wrinkles with no UV exposure at all - no external damage.

There are also definitely different wrinkle morphologies reflecting changes in different layers of skin.

August 25, 2009 | Unregistered CommenterKGH

Dr. Harris,

I knew we can store D for some time, I just wasn't sure of the size of the tank vs. consumption rate. Fortunately, Dr. Mike Eades has just published a takedown of a Golf Digest D "article" and included alink to a sunlight exposure required calculator -

And I found a decent lat/long table to use if your city isn't one of the prebuilt ones -

August 25, 2009 | Unregistered CommenterAnnlee

Dr. Harris,

I would be grateful if you would please comment on this study, and perhaps others like it with which you may be familiar, that stress:
Aging decreases the capacity of human skin to produce vitamin D3."

Thank you for any insight. We in the 40+ crowd may need to eat more herring and/or spend even more time outdoors. What do you think?

August 27, 2009 | Unregistered CommenterSatya

How much sun would you suggest for those of us that burn within 5 minutes in the winter without sunscreen(burn to the point of peeling. Burn to the point of redness is constant without sunscreen, from less than 2 minutes of daily exposure, and burn within 15 minutes with high SPF sunscreen(to the point of peeling))? I am a white skinned person who's family is from the Arctic circle(I now live far south of that, but not in the tropics by far) in terms of area, and have very fair skin(Which my doctors say is the sole reason I burn as much as I do). I burn from UVA rays if I'm sitting within 20 feet of a window with no sunscreen. Many other Irish or similar groups of people have similar problems with sunlight, if we are blonde. I can almost guarantee that I don't get enough Vit D from the sun as I religiously avoid it due to my skin's reaction. Seeing as I'm not planning on moving to northern Norway or Sweden anytime soon, should I avoid the sun, or get the vitamin D from the sun and risk skin cancer and severe burns?

August 27, 2009 | Unregistered CommenterAnn


D production efficiency decreases with age, this is well known. That is why it is best go by serum levels and not guess.


If you are that sensitive, wear a broad brimmed hat and long sleeved shirt and take oral supplements. Get your levels checked if you are not sure of them.

August 27, 2009 | Unregistered CommenterKurt G. Harris MD

Nice post,

Regarding evolutionary rationale for developing lighter skin, I think it' a safe bet that Vitamin D had a role in it. Some of the newer theorists (ie Peter Frost) have promoted sexual selection above all, yet I think that the 10-fold risk factor of getting respiratory infections alone has spiked infant mortality easily enough to make skin color to adapt to make more Vit D.

This immunological theory does not in any way overrule that light skin (+ blue eyes and blond hair) is sexy and therefore preferable - sexual choices could well be part of it the adaptation, driven by good genes hypothesis. (sexual ornament like lighter skin may be an evolutionary signifier of greater genetic disease resistance for opposite sex)

Excuse me for ranting a bit, just tried to contribute something for Vit D's role in human evolution.

PS: I have some critique regarding presupposed optimal 25(OH)D levels for people - I just think that there is some evidence that caucasian people do not need as high levels for bone health than hispanic or black people do. In fact in caucasians, higher than 110 nmol/l is associated with WORSE bone mass index in some epidemiological studies (Bischoff-Ferrari et al.). The same goes for overall death curve - higher than 100 nmol/l have been associated with greater mortality. It might be about high CLO usage and Vit A overdosing, but I think we have not enough information yet to be sure.


Good grief, 100 nmol/l is only 25 ng/dl. I find it totally implausible that a level that low is the upper limit of safety if a white lifeguard can get up to 100 mg/dl. My own level this summer with only sunlight was near 90 ng/dl. In order to give credence to an observational study, one needs a plausible mechanism that would explain increased mortality at obviously physiologic levels, otherwise the association is likely spurious and should be ignored.

I think I'll have to ignore it unless you have some other line of evidence that would make a level of 30 ng/dl more dangerous than 25 ng/dl

Re: light skin - I go with D over sexual selection.

November 28, 2009 | Unregistered CommenterJohnny Bourdeaux, PhD
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