Reggie wrote:Between the clouds, rain and latitude, I get about 0 outside many days. If I were outside in say, sunny Texas, I wouldn't worry about it so much!
From an article from the
Harvard School of Public Health:
A complicating factor in determining how much vitamin D we need to get from diet or supplements is that exposure to sunlight produces vitamin D in the skin, which is then rapidly absorbed in the blood. Thus, a vitamin D intake of 800 IU per day may be too low for a person who rarely gets sun exposure (or for someone living in the north, where vitamin D cannot be made in the late-autumn and winter months). Yet that level of intake may not even be necessary for a person who receives ample sun exposure.
http://www.hsph.harvard.edu/nutritionso ... aminD.html
Yep, us Southerners are lucky, when it comes to vitamin D. I suspect the original paleo people didn't wear a heck of a lot of clothes, because they lived in sunny environments. The clothes probably came thousands of years later, as some tribes moved into colder habitats.
The
American Academy of Dermatology Association, of course, opposes getting vitamin D through the skin:
"It is known that there is a high risk of developing skin cancer from repeated and intentional ultraviolet B exposure to boost vitamin D levels; the latter can be safely achieved by nutritional supplements," said Dr. DeLeo. "Skin cancer is an epidemic in this country and recommending increased UV exposure with claims that sunlight somehow promotes good health is highly irresponsible."
Furthermore, they say:
Photosynthesizing vitamin D through natural sunlight is maximized after 20 minutes of ultraviolet B (UVB) exposure, with extended sun exposure providing no additional benefit but instead increasing the likelihood of photodamage and skin cancer.
Vitamin D uptake through the skin is sort of a "Catch 22" situation, in that as we age, we need more vitamin D, but aging skin does not absorb vitamin D as readily:
"When people age, their skin becomes less equipped to process vitamin D absorption through incidental sun exposure," said Dr. DeLeo. "Since their daily vitamin D requirements are so much higher than their younger counterparts, it is very important that they take vitamin D supplements and increase their intake of vitamin D enriched foods such as milk and other fortified dairy products, fortified orange juice and certain kinds of fish."
http://www.medicalnewstoday.com/articles/23771.php
If you want to quantify what it needed, the number to shoot for is serum 25-hydroxyvitamin D, [25(OH)D], concentrations equal to or greater than 75 nmol/L, according to the
Journal of Clinical Nutrition.
http://www.ajcn.org/cgi/content/full/85/3/649
These folks don't exactly agree with the The
American Academy of Dermatology Association, (that is, they don't propose a blanket condemnation of sun exposure), and they endorse obtaining vitamin D through any of the conventional sources:
Correction of low 25(OH)D concentrations can happen only if some or all of the following are implemented: the encouragement of safe, moderate exposure of skin to ultraviolet light; appropriate increases in food fortification with vitamin D; and the provision of higher doses of vitamin D in supplements for adults.
The main problem with getting vitamin D from sunlight, of course, is the lack of a reliable, quantifiable way to measure it. Common recommendations are usually based on something like "
Fifteen minutes of sun exposure two to three times a week (to the face, hands, feet...)". So what latitude is that based on? Arizona? Alaska? Nebraska? Does anybody know? Does the original author of that statement even know?
Here in the South, many construction workers, and especially roofers, traditionally work all day in the sun wearing shorts, and no shirt, (well, except for female construction workers, of course). At the other extreme, many/most of those who work indoors, usually get virtually no sun at all, while they are working, and if they get any sun exposure, it will have to come from recreational pursuits. Farmers, ranchers, construction workers, etc., are somewhere in the middle, and mostly wear protective clothing, but their faces, and maybe their hands, are exposed to the sun for much of the day.
Is there an epidemic of of skin cancer among roofers? I dunno, but they continue to do it, year after year. Are they healthier than most? Again, I don't know, but they are dang sure gettin' enough vitamin D.
The bottom line - I don't get as much sun as I used to, (I'm one of those guys who used to work in the fields without a shirt, sometimes), but I'll probably be looking into boosting my vitamin D supplement from the current level of 400 IU, to maybe close to a thousand, even though I live in sunny Texas.
Tex
