Marks Daily Apple
Serving up health and fitness insights (daily, of course) with a side of irreverence.
3 Jun

Vitamin D: Confounding Factors

suncloudYesterday I recommended 4000 IU of vitamin D each day as a good starting point for most people. Though, it’s difficult – nay, impossible – to provide a perfect, universal prescription for vitamin D3 intake. People, and their lifestyle behaviors and environmental conditions are just too different. It’s like with diet. Everyone does well with the basic building blocks, stuff like meat, fat, vegetables, fruit, and nuts, but the optimal ratios are going to differ for individuals based on genetics, dietary history, activity level, and glucose tolerance. Everyone needs vitamin D, but multiple confounding factors must be taken into consideration to determine the right dosage. To start with? Yes, 4k is a good starting point. From there, though, things get considerably more complicated – as they always do.

Now, I don’t want to overcomplicate things, however. The same basic advice holds: get unfiltered sunlight, avoid burning, and take supplements when sunlight is unavailable. But I do want you to be aware of certain factors – environmental, climatic, dietary, genetic, etc. – that may affect vitamin D3 production, requirements, and availability.

Skin Color

A person’s skin color affects his or her ability to create D3 in the skin. The darker you are, the longer you must remain exposed for optimal D3 production. Dark skin also protects you from the sun – which is probably why melanin-rich black skin was the default hue for early humans living in equatorial Africa. Among those of us who moved to cooler climates with actual seasons, lighter skin with greater sensitivity to sunlight was selected.

But damn if we aren’t a mobile people, and that mobility throws a monkey wrench into the whole thing. The whitest white guy with Celtic blood running through his veins can live in sun-drenched Southern California, just as a black woman several generations removed from Nigeria might have settled down in Norway. Each is imbued with a vitamin D3 production capability that “conflicts” with their current locale. As far as melanin content and resistance to sunlight is concerned, they’re on permanent vacation. Have they outpaced natural selection? A bit, but they can avoid serious complications by knowing the facts and acting accordingly. Dark skinned folks will need more sun – or supplements to make up for it – while lighter skinned folks need less sun to produce D:

10-45 minutes full sun (without burning) for light skin
2-2.5 hours full sun for dark skin

Diet

No food enters our body in a vacuum. It is a mistake to only think of individual nutrients or vitamins without giving thought to how they might react with the hundreds of other substances you take in on a daily basis. Vitamin D is one of the biggest. What we eat has powerful effects on vitamin D metabolism.

Magnesium – Magnesium is important for bone health because a sufficient amount enables the mobilization of active vitamin D3 – calcitriol. One study even showed that magnesium deficiency resulted in 50% less calcitriol, increased inflammatory markers in the bone, and lowered bone mass.

A Primal Blueprint diet high/sufficient in magnesium may reduce your need of D3 supplements. If you’re getting plenty of magnesium through leafy greens, nuts, and supplements, you may want to stick to D3 from sunlight or in smaller doses closer to 4,000 IU.

Meat –It has been shown that a Western style plan of omnivory, with particular emphasis on meat, dairy, and eggs, protects against rickets in the presence of severe vitamin D deficiency. Dunnigan thinks the meat is responsible, and that vitamin D deficiency is necessary but not sufficient for rickets. You’ve also got to avoid the meat to really make the D3 deficiency manifest as something bad.

As Peter said, you can get away with vegetarianism in the tropics, where D3 is plentiful. Moving north requires meat in the diet. It’s probably true that a Primal eating strategy rich in animal protein makes complications from vitamin D3 deficiency uncommon, even without getting much sun or taking many supplements.

GrainsGrains in the diet decrease calcium absorption, thus increasing the demand for vitamin D. Eat grains and you’d better be getting plenty of good sunlight.

Don’t eat grains.

Vitamin A – A heated debate over vitamin A and vitamin D (with a bit of K2 sprinkled in) rages on. The Vitamin D Council boys claim A antagonizes and competes with D, while Chris Masterjohn and the WAPF stress balance of the two for proper function.

Rather than demonize one and exalt the other, just get sun, take supplements when you need them, and eat plenty of beta-carotene in the form of veggies, along with some preformed retinol in the form of liver, eggs, and other animal fats. Don’t take cod liver oil for the DHA/EPA; take half a teaspoon or so for the vitamins. Stick to fish oil for your omega-3s.

PUFA/SFA – People report increased resistance to sunburn since replacing dietary PUFA with SFA. I’ve definitely noticed similar effects, but I was unable to bring up any literature confirming it. Anyone know more?

Pollution

Remember how they used to warn us about CFCs depleting the ozone layer and letting in too much UV light? That was probably a fairly valid warning, seeing as how full spectrum UV in naturally occurring ratios is what we should be getting. Any kind of imbalance deserves wariness. Strangely enough, now the real issue is insufficient UVB caused by too much ozone. One study found that “urban tropospheric ozone” – a benign-sounding name for manmade air pollution – was to blame for widespread vitamin D deficiency among physically active urban Belgian women who spent plenty of time outdoors in the summer. Rural women doing the same activities at the same time of year were mostly free of deficiency.

In a rare stroke of irony tinged with good news, researchers are even now estimating that the benefits of excess solar radiation due to ozone depletion outweigh the downsides.

Urban sunlight probably isn’t as potent as rural. If you’re primarily an urban dweller who’s unable to get his or her D3 levels to budge despite dedicating time to sunlight, maybe get outside city limits on a regular basis. Go for a hike, have a picnic.

Clouds

Clouds are another confounding factor for vitamin D, but in a very convoluted way. On a completely overcast day with heavy clouds blanketing the sky, 70-90% of the UVB is blocked, which translates to greatly reduced potential for natural D production. Partly cloudy skies, however, have a different effect. The UVB can actually reflect off of the denser clouds and increase in intensity, effectively scattering itself all over the place.

The same thing can happen with UVA, too, but the effect is pretty meager.

Full cloud coverage blocks most of it out. Spotty coverage blocks direct UVB, but may increase effective UVB. As long as you’re aware that UV is still present on semi-cloudy days, you can use your judgment.

Sunscreen

Slather it on, they tell us, and we do it – usually. But does it really protect us? I mean, our proclivity to follow the experts’ advice on sunblock and sun exposure has proven highly effective in the fight against melanoma, right?

Melanoma incidence is way down (it’s not (PDF)).

As sunscreen usage and sales have skyrocketed, skin cancer has plummeted (the opposite has happened).

What’s the deal? Most of the popular sunscreens on the market only offer meaningful protection against UVB rays. I get that. As much as I love a nice dose of vitamin D, too much UVB exposure can lead to sunburns and skin damage. But in letting through most of the UVA while blocking out UVB, they are doing users a massive disservice. The UVA ends up being a huge problem because people are staying out longer without burning. They figure they’re safe, but it’s a false sense of security: isolated UVA exposure (along with decreased D) seems to increase the chance of developing melanoma, the really dangerous kind of skin cancer.

In the end, it seems like getting full spectrum UV is essential for obtaining D3 and protecting yourself. In this case, what works best is what’s most natural – full spectrum sunlight without burning.

(Here’s a cool hack for figuring out how much vitamin D you might be getting based on several factors, like cloud cover, surface altitude, latitude, time of year, etc. It’s imperfect, but a good general guide that’s fun to play with.)

Keep the questions coming and stay tuned for future coverage of vitamin D. Thanks for reading, everyone.

You want comments? We got comments:

Imagine you’re George Clooney. Take a moment to admire your grooming and wit. Okay, now imagine someone walks up to you and asks, “What’s your name?” You say, “I’m George Clooney.” Or maybe you say, “I’m the Clooninator!” You don’t say “I’m George of George Clooney Sells Movies Blog” and you certainly don’t say, “I’m Clooney Weight Loss Plan”. So while spam is technically meat, it ain’t anywhere near Primal. Please nickname yourself something your friends would call you.

  1. The sunscreen part is particularly interesting. I seem to notice that a lot of things recommended for public health on which supposedly “all scientists agree” turn out to not actually be working. The standard diet recommendations vs. the primal diet is a perfect example.

    John Solter wrote on June 3rd, 2010
  2. I loved this part…

    “Eat grains and you’d better be getting plenty of good sunlight.

    Don’t eat grains.”

    Loved these 3 posts on sunshine. I make it simple…

    Go outdoors as much as I wish. If I am pink and it burns, then I know I got too much sunshine. No problem, stay inside more for a few days, then move on.

    I also know that my primal lifestyle, including diet, helps prevent myself from burning.

    Primal Toad wrote on June 3rd, 2010
  3. I hate putting on sunscreen, and the fact that nearly every lotion makes my face break out made me want to use it even less! Interestingly enough though, I actually break out less when my face is tan in the spring/summer, even though I’m sweating more.

    I had always heard that you can still get a sunburn on an overcast day, but if the burn-causing UVB rays are 70-80%blocked then how can that be the case?

    Hannah wrote on June 3rd, 2010
    • I used to have acne… then I went primal and I am now acne free.

      I haven’t put anything on my face for the past 2-3 months. I simply splash water on my face and that is it. Nothing else, really.

      I would forgo putting on sunscreen, especially if you have acne. The chemicals in sunscreen will prevent you from ever being clear. Eat primal, seek shade when you get too hot, and just don’t bath for 2-3 hours a time.

      Primal Toad wrote on June 3rd, 2010
  4. Another great post! Thank you for the resource and advice!

    And don’t forget the toxicity of many sunscreen ingredients! Here is the recently released Environmental Working Group survey of sunscreens:
    http://www.ewg.org/2010sunscreen/

    I just threw away my Coppertone. And I did a beauty product purge too. I am transitioning to those with ingredients I can pronounce and that come from named plant sources. While still processed, at least it’s a step in the right direction!

    Kristy A. wrote on June 3rd, 2010
  5. i am dark-skinned, but i could be out in the sun for literally 5-10 minutes and get a tan. is this a good thing or a bad thing? does that mean that i quickly make vitamin d from the sun?

    vivian wrote on June 3rd, 2010
  6. Interesting about the PUFA/SFA and burning. I was out in the sun all weekend (with no sunscreen) for the first time since going primal this winter, and my incandescently pale skin didn’t burn. Previously, 20 minutes in the sun would scorch me. Nice!

    Jenn wrote on June 3rd, 2010
  7. I have also heard that about PUFA increase the rates of skin cancer. I think I read it in a Crossfit article.

    I’m sure you understand all of this much more better than I could Mark, but I think I read that when you have too much PUFA, it actually replaces the saturated fats in your lipid bilayer of your cell walls. This makes for a “floppy” cell, making it easier for UV A rays to penetrate the skin.

    That’s what I read somewhere, anyway.

    Good luck on finding more literature on that!

    Caitlin wrote on June 3rd, 2010
  8. “PUFA/SFA – People report increased resistance to sunburn since replacing dietary PUFA with SFA. I’ve definitely noticed similar effects, but I was unable to bring up any literature confirming it. Anyone know more?”

    Stephen Guyenet as posted on this. It’s not PUFA to SFA, it’s omega-6 to omega-3.

    See here:
    “Thus, the amount of linoleic acid in the diet as well as the balance between omega-6 and omega-3 determine the susceptibility of the skin to damage from UV rays.”

    http://wholehealthsource.blogspot.com/2009/03/skin-texture-cancer-and-dietary-fat.html

    The effect also seem to be present in humans:

    “Conclusions: Overall, these results indicate that an excess energy-adjusted intake of linoleic acid and a lower consumption of soluble carbohydrates may increase melanoma risk.”

    http://journals.cambridge.org/production/action/cjoGetFulltext?fulltextid=632352

    (Link opens a pdf.)

    Tuck wrote on June 3rd, 2010
  9. What about ozone? There is little ozone in the southern hemisphere and the sun definitely burns here.

    Janet wrote on June 3rd, 2010
  10. I went Primal the beginning of February and by the end of March I noticed I wasn’t getting sunburned like I used to. I had read comments on this site early on about others getting that effect, but never dreamed it would happen to me.

    When it did, it drove me crazy that I couldn’t find an explanation why no matter how much I Googled. The one interesting thing I did find at that time was a blog entry from a guy who had recently gone raw (and my impression was it was vegan raw). He too noticed that he was no longer burning and said he had heard other rawists (is that a word?) talk of having a similar effect. He attributed the effect to no longer eating those evil animal foods. Of course I laughed as animal food was about ALL I was eating at the time – vegetables not being one of my strong points.

    So I wondered, we both had the same effect – decreased sunburning – but our diets had nothing in common. I was leaning towards contributing the cause to decreased carbs in the diet, but carbs was ALL he ate. Anyway, I didn’t find anything further so I gave up the search and just accepted the benefit.

    Then about a month ago I was on a site and listening to an audio interview of a doctor who said that higher glutathione levels gave protection against sunburn. Boy did my ears perk up. Unfortunately it was just a side comment so he did not elaborate. (For those who don’t know, and I was one of them, glutathione is an antioxidant produced in almost every cell in the body.) However he did say that when people switch to a healthier diet that their glutathione levels tend to go up.

    That’s all I know about that for what it’s worth. I thought it was pretty interesting though.

    Julie wrote on June 3rd, 2010
    • I have been primal since last Thanksgiving. I used to go from white to stroke (my face and ears would burn beet red) every time out in the sun. Now I run around without a shirt, play golf for hours, kayak, etc. and I haven’t burned once. Still looking for explanation…

      CFurg wrote on June 11th, 2012
  11. Grains – Grains in the diet decrease calcium absorption, thus increasing the demand for vitamin D. Eat grains and you’d better be getting plenty of good sunlight.

    This is so true and I always used to wonder why people in India, Italy and those regions of the world eat grains and still stay lean and slim this is because they get lots of sunlight and stay active outside most of the time. I dont eat grain but this is something that always made me wonder. What is different that they are doing.

    Irshad Khan wrote on June 3rd, 2010
    • I’d also be interested in that answer. While I limit carbs, and eat nuts instead, I wonder how the Mediterranean people do it so well….?

      Picaro wrote on June 5th, 2010
  12. What would you suggest for people who tan to start, but burn with too much exposure to the sun, in regards to sun screen? In the summer months I’m outside constantly during the day, and while I get a nice base tan, I also will burn without sunscreen after about 45 minutes.

    Andy wrote on June 3rd, 2010
  13. yo, I am a big fan of the primal bluprint and your blog but here is my delemma: Sunscreen. I work 8 hours a day, 6 days a week outside and I get sunburnt like mad, anyways do you have any alternitives to sunscreen.

    D Monk wrote on June 3rd, 2010
    • Try Invisible Zinc or similar zinc-based sunscreens. They aren’t absorbed as readily into the skin & give a better UVA spectrum protection.

      Jamie wrote on June 3rd, 2010
  14. What about not washing with soap for 48 hours after sun exposure to let the skin do it’s work? I read that somewhere…

    SuperMike wrote on June 3rd, 2010
  15. Here is a good site that gives more information like Mark’s about vitamin D and such… Sorry, if posting other sites on your comments is not allowed. Hope this helps someone!

    http://www.healingnaturallybybee.com/articles/sun.php

    Nightsdisguise wrote on June 3rd, 2010
  16. As a fair-skinned person, I was – prior to vitamin D & omega 3 supplementation – unable to spend long in the sun. The past New Zealand summer gone, I didn’t use sunscreen at all & barely got more than a little pink despite being in the sun all day.

    http://primalmuse.blogspot.com/2010/04/farewell-summer-sun.html

    Melanoma is on the rise and has been since the 1940′s…. for INDOOR WORKERS ONLY!

    Increased UVA Exposures & Decreased Cutaneous Vitamin D3 Levels May Be Responsible For The Increasing Incidence Of Melanoma.

    Cutaneous malignant melanoma (CMM) has been increasing at a steady exponential rate in fair-skinned, indoor workers since before 1940. A paradox exists between indoor and outdoor workers because indoor workers get three to nine times less solar UV (290-400 nm) exposure than outdoor workers get, yet only indoor workers have an increasing incidence of CMM.

    Godar DE, Landry RJ, Lucas AD. Increased UVA exposures and decreased cutaneous Vitamin D(3) levels may be responsible for the increasing incidence of melanoma. Med Hypotheses. 2009 Apr;72(4):434-43. Epub 2009 Jan 19.

    http://primalmuse.blogspot.com/2010/03/sunlight-robbery.html

    I work as a clinical nutritionist and use a weight recommendation for vitamin D dosing – 1000IU per 15kg (I think the Vitamin D council uses 1000IU per 25lb).

    Jamie wrote on June 3rd, 2010
  17. Oh… and a good paper on nutritional factors that might increase sun protection;

    http://www.dr-baumann-international.co.uk/science/Nutritional%20Protection%20against%20Skin%20Damage%20from%20Sun%20Light.pdf

    Jamie wrote on June 3rd, 2010
    • Jaime, thank you for posting that link. I was trying to find something like that when I was Googling for information back in March.

      I haven’t done a slow read through the paper yet, but after a quick scan it does seem to indicate that antioxidant activity does have something to do with UV protection. Interesting ….

      Julie wrote on June 4th, 2010
  18. Is it possible to consume toxic levels of vitamin D?

    I had a problem with my skin cracking around my mouth a few years ago and my doctor told me it was due the cod liver oil capsules I was taking.

    I attribute it to the fact that I’m now overly sensitive to vitamin A since taking acutane.

    Is it possible to have a reaction like this with vitamin D from supplements?

    Jessica wrote on June 3rd, 2010
    • Jessica, you would have to be sky-high with vitamin D levels to see any real toxicity. I have read persistent levels above 500nmol/L might start to cause problems over the longer term. And this is a hard level to get to through sun exposure and supplementation.

      Depending on how long it is since ceasing Roaccutane therapy, it is likely to be vitamin A. Cracked lips, dry nose, etc, are all side effects of roaccutane therapy (essentially hypervitaminosis A). The A in CLO might be enough to push you back up to that level again. It took me at least 3 years before I lost my photosensitivity due to roaccutane therapy.

      Adequate vitamin K intake looks like it might be protective against vitamin D toxicity – helps keep calcium where it should be & not where it shouldn’t.

      Jamie wrote on June 3rd, 2010
      • Thanks for the info. I guess this is just another reason not to take accutane.

        Jessica wrote on June 4th, 2010
  19. I’ve heard that our bodies can produce 10,000 – 20,000 iu of D3 in 30 minutes of exposure to full sun. How much skin needs to be exposed to reach those levels? Face and hands? Shirt removed? Bare assed Grok naked? Does the angle of sunlight make a difference? Can we be standing up or should we lie down?
    I think it may be easier to take the supplements! ;–)

    Dirk Fetherstonhaugh wrote on June 3rd, 2010
    • The sun needs to be 45deg above the horizon to get enough UVB radiation at ground surface level. SO the common advice from the likes of the Skin cancer societies to get sunlight exposure before 10am and after 4pm for vitamin D doesn’t hold. Sun exposure during solar noon is best.

      Jamie wrote on June 3rd, 2010
  20. Excellent posts on Vitamin D Mark! I’m brown skinned, I imagine I would need about 1-2 hours of sun exposure to get the required amount of Vitamin D. I live in a place where we have decent sunlight for only about 50 days in a year and I’ve been supplementing with 5000 IU.

    maba wrote on June 3rd, 2010
    • I checked the Vit D calculator and for today’s date and weather, I need 11.5 hours of sun exposure LOL! And this doesn’t consider my dark skin.

      maba wrote on June 3rd, 2010
      • nope. the result shows when, and for how many hours a day the sun is strong enough to generate vit D at all. you can check this by dialing a different month (say, in winter), and you will see that the resulting duration shrinks.

        qualia wrote on June 3rd, 2010
  21. Here is a link to a Vitamin D calculator that is simpler than the one Mark linked to.

    http://www.thevitamindcure.com/calculator/

    It is on the site of the author who wrote The Vitamin D Cure so you have to put in your email address, but it’s good because it takes into account your weight and age.

    Julie wrote on June 3rd, 2010
  22. Thanks, Mark, for highlighting the relationship between skin pigment and UVB->Vit D synthesis.

    The Vitamin D council have been all over this for some time and I’ve posted a bit more backgound on the issue here:

    http://healthmanblog.com/2010/05/18/racial-opportunities-vitamin-d-again/

    Thanks for bein’ you!

    Keith wrote on June 3rd, 2010
  23. Hello,

    Personally I use a UVB meter to time my skin exposure based on my skin type in summer. In winter I use my body weight in pounds times 20, the result being my daily D3 in international units.

    The reason to use your body weight is that vitamin D gets caught up in fat, if you weight more, you need more.

    A personal UV meter looks like this;
    http://www.popularmechanics.com/cm/popularmechanics/images/Vl/uv-meter-470-0709.jpg

    Tom wrote on June 3rd, 2010
  24. Just read an interesting article on paleochix.com about using coconut oil in place of sunscreen. going to try it this weekend, first me then my kids…..sounds amazing and like it really works. I have noticed too that i seem to get more brown in the sun than I used too when I ate grains. Now I use sunscreen but do not burn like i used to with protection on. Very eager to try the coconut oil!

    MaryLou wrote on June 3rd, 2010
    • Regardless of whether it protects from the sun, it feels SO GOOD on your skin! I recently stopped using all “fake” lotions and started using coconut oil instead and my skil feels FANTASTIC. I never suffer from overly dry skin anymore.

      Also I must attest to the PBs power of protection against the sun. Being very pale skinned, I would burn in 20 minutes or less! I recently spent all day in the sun gardening, and I didn’t burn at all. Woot!

      Chandra wrote on June 3rd, 2010
  25. If you want to research sunscreen/sunlight exposure. Check out this web site:

    http://www.ucsd.tv/vitamind/

    Watch the video: Skin Cancer/ Sunscreen – the Dilemna

    Susaan wrote on June 3rd, 2010
  26. I am a red-head who has been on the PB since March and I can assure you that I am able to withstand sun burn much more easily now.

    I was out in the direct sun for about 45 minutes before I started getting concerned about sun burn. I could feel that I needed to get indoors and I was afraid I would be burned since I did not use lotion, but I was okay.

    Prior to PB, I would get like this after only 10-15 minutes.

    Chris wrote on June 3rd, 2010
  27. Some scientists have theorized that white skin is an evolutionary adaptation to the grain-based diet of post-agricultural Nothern Europeans. At northerly latitudes where vitamin D synthesis is difficult, a vitamin D deficient, grain-based diet increased selective pressures for light skin. Interestingly, native populations maintaining a diet rich in animal products (especially fish) have retained their dark complexions (e.g. Canadian/Siberian Inuits) even at latitudes where vitamin D synthesis via sunlight is virtually impossible.

    Taylor wrote on June 3rd, 2010
  28. There is a book, Saturated Fat May Save Your Life by Bruce Fife that has some material on PUFA intake and skin cancer.

    Harps wrote on June 3rd, 2010
  29. Hi, don’t know why but I too have noticed the improved resistance to sunburn since being on a primal\paleo diet.
    Whether it is due to reduced inflammation, less PUFA (or even more vitamin D in skin!) or even all of the above I have no idea. But there is definitely something in it. If you look round on the internet there are a lot of individual anecdotal accounts about this. OB

    ob wrote on June 3rd, 2010
  30. A little off topic here. I told a friend (I call him a vampire) who never goes in the sun (and when he does he is white from the sunscreen) and eats grains that his brittle bones are going to snap in half at the age of 40…..too harsh? His father just had a hip replacement at 60 years old. He avoids the sun also….coincidence? I THINK NOT!

    Aaron Curl wrote on June 4th, 2010
  31. as you age the body doesn’t process the production of vitamin D quite as well… a healthy liver is essential to help the body convert uvb to vit d…

    you need uvb to make vit d, but uva destroys vit d …one of mother nature’s checks and balances to ensure our bodies stay in balance. …glass blocks uvb rays but does not block uva- so if you are in a car or sitting in the sunshine inside a building for long periods of time you can actually be depleting the vit d…

    because everyone processes vit d differently, blood testing is the only way to determine how much vit d you need… the 25(OH)D test is the one that should be used… if your levels are below 20 ng/ml you are considered seriously deficient… optimal levels are 50 – 70 ng/ml and levels between 70 -100 ng/ml are therapeutic for treating cancer and heart disease…

    if your doctor gives you an Rx for vit d, it is probably for d2 which is the synthetic form and is inferior because it binds poorly with protien and has a shorter shelf life. It’s better to supplement with Vit D3, which is natural and you convert it to a useable form 500 times faster than vit d2…

    Marti wrote on June 4th, 2010
  32. I posted this yesterday, but it’s still awaiting moderation (due to links maybe?)…

    “PUFA/SFA – People report increased resistance to sunburn since replacing dietary PUFA with SFA. I’ve definitely noticed similar effects, but I was unable to bring up any literature confirming it. Anyone know more?”

    Stephen Guyenet as posted on this. It’s not PUFA to SFA, it’s omega-6 to omega-3.

    See here:
    “Thus, the amount of linoleic acid in the diet as well as the balance between omega-6 and omega-3 determine the susceptibility of the skin to damage from UV rays.”

    link removed…

    The effect also seem to be present in humans:

    “Conclusions: Overall, these results indicate that an excess energy-adjusted intake of linoleic acid and a lower consumption of soluble carbohydrates may increase melanoma risk.”

    link removed…

    (Link opens a pdf.)

    Tuck wrote on June 4th, 2010
  33. Mark, what do you think about for people who have already had melanoma? I’ve got a ton of moles and see the dermatologist about every six months, and they say that there’s a correlation between where you’ve gotten sun and where the cancers come up. Of course, I also just got my blood work and found out that I’m deficient in Vitamin D. On the one hand, I don’t spend any significant length of time outside without sunscreen on, on the other hand, mentally I can’t grasp how I’m not supposed to be outside without spf 5000 on.

    Patrick wrote on June 4th, 2010
  34. Hello,

    If you want to learn about sunscreen versus melanoma go here;
    http://www.ucsd.tv/search-details.aspx?showID=15770

    If you want to see how melanoma incidence correlates to the populariaztion of sunscreen in the mid 1960′s go here;
    http://1.bp.blogspot.com/_2BTNH5l9XNU/Sm5eHrZCSpI/AAAAAAAAAPg/6AjCndCRm_Q/s1600/sunscreen2.JPG

    Tom wrote on June 4th, 2010
  35. The fact is, and it is most surely a fact, the sun’s UV rays are primarily responsible for photo-aging of the skin. No getting around this fact. It’s just too easy to use a really good sunscreen with zinc oxide. Z-cote offers great protection with little to no whitening.
    And if your getting your D3 levels checked and supplementing with at least 5,000iu d3 daily….you should be fine.

    Robert wrote on June 4th, 2010
  36. If you want to get down to basics we evolved as naked apes under the sun, with no sunscreen for five million years.

    If you check the research they are just begining to learn there are other photoproducts produced by the skin.

    You can fight five million years of evolution but odds are you will lose.

    Tom wrote on June 4th, 2010
  37. Looks like you don’t actually have to roast in the sun to get your vitamin D the natural way. Sitting under a shady tree can also do the trick as long as you can still see lots of sky. It may take a tad longer but when it’s 100 degrees outside, it will be more pleasant, and I suspect that’s exactly how Grok would have done as well. Here’s a link to how the so called ‘dangerous’ sun can still get at you when you are in the shade:
    http://www.anapsid.org/uvbounce.html

    Eva wrote on June 5th, 2010
  38. I found this site …an app for your phone that can calculate based on where you are & the weather the approx Vit D you would be exposed to outside.

    Has anyone used this?

    http://dminder.ontometrics.com/

    Brenda S wrote on July 10th, 2014

Leave a Reply

If you'd like to add an avatar to all of your comments click here!

© 2014 Mark's Daily Apple