Vitamin D - The Sunshine Vitamin
Vitamin D is NOT a vitamin; rather it is a steroid hormone that is synthesized from the effects of sunshine upon cholesterol.
Nor is it a nutrient that can be easily obtained from food. For all practical purposes, vitamin D is NOT supplied by your diet in any amount that would come remotely close to meeting your optimum daily requirements.
Vitamin D comes from Sunshine
Vitamin D's only natural source comes from the effects of Sunlight (i.e., the ultraviolet-B spectrum between 290 and 315 nm) upon bare and unprotected skin. In the Northern hemisphere at latitudes above 37°N sunning outside between October and February, or the winter months in the Southern hemisphere for latitudes below 37°S; sunshine will produce absolutely no vitamin D. A good rule of thumb for determining if vitamin D is being produced by sunlight is that ultraviolet-B rays are only beneficial when your shadow is shorter than your height.
Globally, looking at the sunshine situation, just about the entire Southern hemisphere can synthesize vitamin D all year round. The Northern hemisphere, however, suggests a lot bleaker picture since sizable population areas cannot. In the New World, Virginia and above cannot synthesize vitamin D during the winter months. In the Old World, nor can all of Europe, Russia, and everything above the very top of Africa. As latitude rises, gets bigger, or farther away from the equator even summer synthesis of vitamin D is reduced.
If you live north of the 37th parallel, it is useless to sun outside during the winter months., In that case, your only other alternative is vitamin D supplementation or visiting a tanning salon. If your preference is using a tanning salon then, of course, you must investigate as to whether the particular tanning beds produce the ultraviolet-B spectrum between the 290 and 315 nm wavelengths, with preferably none of the ultraviolet-A skin aging rays. As long as you limit your tanning sessions to only ten minutes, using a full body tanning bed for vitamin D synthesis should be a safe alternative.
Sunshine and Vitamin D
Noontime is the best time of Day for vitamin D synthesis from sunshine.
Contrary to popular opinion, you should ONLY sunbathe for vitamin D during what is usually considered to be the worst time of the day, between 10 a.m. and 2 p.m., for sunburns. "The best time of day for vitamin D production is near solar noon, when the ratio of UVB to UVA is highest." The ozone layer absorbs ultraviolet-B radiation above 290 nm that is responsible for producing vitamin D-3 in the skin. When the angle of the sunlight reaching the Earth's surface is very oblique (i.e., early morning, late afternoon, and winter), sunlight passes through more ozone, which effectively absorbs the ultraviolet-B rays.
It gets even worst, sunning yourself in the late afternoon after 3:00 p.m., is actually more dangerous for you. Consistently sunning in the late afternoon will actually increase your risk for melanoma. It has to do with the ratio of UVB to UVA light waves. In the late afternoon, the intensity of UVB rays are reduced by 50%, while the UVA rays are just as strong as ever.
The amount of body surface skin area exposed to sunlight is more important than the duration of exposure for maximum vitamin D production. The idea is to get full body sun during a very brief period of time. Never allow your skin to redden, or get sunburn. Sunbathing during other parts of the day takes a much longer time period to produce a lot less vitamin D, and results in more skin damage.
"Sun exposure was statistically significantly inversely associated with risk of death from melanoma, regardless of the measure used. ... Individuals who had ever been severely sunburned ... or who had high levels of intermittent sun exposure ... were less likely to die from melanoma than individuals who had never been severely sunburned or who had low levels of intermittent sun exposure, respectively.
The presence of solar elastosis [premature aging of the skin due to prolonged exposure to sunlight] was also inversely associated with death from melanoma."
Under ideal conditions, "a single exposure to summer sun in a bathing suit for 20 minutes produces the equivalent of 15,000 to 20,000 IU of vitamin D-3" in Hawaiian surfers. Beyond sunning at higher latitudes, biological factors that can affect vitamin D synthesis include skin pigmentation, prescription medication, body fat content, any fat absorption problems, and chronological age. A 70-year-old senior citizen produces approximately 4 times less vitamin D through cutaneous synthesis compared with a 20-year-old. Since cholesterol is a precursor to vitamin D, reducing cholesterol blood levels with prescription medication could conceivably inhibit the synthesis of vitamin D by sunlight, especially by any individual experiencing muscle pain. Logically, trying to synthesize vitamin D with sunshine exposure would be counterproductive with extremely low blood cholesterol levels.
for U.S.A. based shoppers
With repeated sunshine exposure you should expect to experience a darkening of your exposed skin. Meeting your vitamin D needs with repeated sun exposure is anything but predictable. How people respond to UVB radiation exposure varies among individuals causing some to have sub-optimal vitamin D levels despite abundant sunshine exposure. Would anyone ever expect that low vitamin D levels would be a problem in Hawaii? Yet, a research study has reported exactly that. In this study, adult test subjects with a mean age of 24 in Honolulu, Hawaii (latitude 21°N) who seemingly got adequate UV exposure (a mean sun exposure without sunscreen of 20 h/wk) had only a mean blood serum level of 30 ng/ml. Meaning that a few test subjects actually had lower levels. Thus, sub-optimal vitamin D status may occur despite adequate sunshine exposure.
Just from working outdoors (ex. landscaping, construction, farming) all day (38 h/wk), the sunlight exposure in America (Nebraska, Kansas, and North Dakota) to be expected is roughly equivalent to a daily oral vitamin D-3 dose of 2,780 IU; due to the minimal amount body surface area being normally exposed.
The intelligent use of broad-spectrum sunscreen still protects your skin from the harmful rays of sunshine.
Everyday after having achieved a maximum amount of vitamin D synthesis, further production will automatically be shut down by your body. It is a mistake to believe that you can force your body into making unlimited amounts of D-3, in a single day. Thus, after having sunned yourself in a controlled fashion at midday for ten to fifteen minutes, it is still advisable to apply a broad-spectrum sunscreen to any exposed areas of your body, particularly if you will be outside in the sunshine for any extended period of time.
Of course, it would be advisable to remove any applied sunscreen by bathing before you attempt to synthesis any more vitamin D with Sunshine.
Positives of Vitamin D Synthesis from Sunshine
Synthesizing vitamin D from sunshine is the only natural way of getting this steroid hormone. Cholecalciferol, or D-3, is assumed to be the single active agent. There maybe other things produced by exposure to sunshine, hitherto unknown, that may be shown in the future by scientific research to be important to your health. The only way to be sure that you are covering all your health bases is to get sunshine while it is available at least in the summertime.
Negatives of Vitamin D Synthesis from Sunshine
While getting vitamin D from the sunshine is free, it comes at a high cost. Obviously, this method takes a lot of time and planning to quickly change into a skimpy bathing suit and lay out in the sun on both sides even if it is only for ten minutes. Further, anybody holding down a job is going to be hard pressed to sun at noontime in a work setting. The biggest negative is that it is very hard to calculate exactly how much vitamin D your body is producing. Furthermore, during the winter, for a lot of people using a tanning bed costs a lot more money than supplementing with vitamin D does. As a result, devoted sunbathers should take a vitamin D blood test more frequently. Further, long term exposure to sunshine will eventually age your skin.
For these reasons, the Natural Health Perspective views natural vitamin D synthesis as more of a supplemental way of occasionally getting additional vitamin D, such as on the weekends.
Please read our Medical Advice Disclaimer.
Please read our Nutritional Supplements Disclaimer.
vitamin D status despite abundant sun exposure.
Binkley N, Novotny R, Krueger D, ...
Clin Endocrinol Metab. 2007 Jun;92(6):2130-5. Epub 2007 Apr 10.
of above average summer sun exposure on serum 25-hydroxyvitamin D
and calcium absorption.
Barger-Lux MJ, Heaney RP.
J Clin Endocrinol Metab. 2002 Nov;87(11):4952-6.
role of vitamin D in cancer prevention.
Garland CF, Garland FC, Gorham ED, Lipkin M, Newmark H, Mohr SB, Holick MF.
Am J Public Health. 2006 Feb;96(2):252-61. Epub 2005 Dec 27. Review.
prevalence of vitamin D inadequacy and implications for health.
Mayo Clin Proc. 2006 Mar;81(3):353-73. Review.
and requirements of vitamin D for optimal health: a review.
Grant WB, Holick MF.
Altern Med Rev. 2005 Jun;10(2):94-111. Review.
serum 25-hydroxycholecalciferol response to extended oral dosing with
Heaney RP, Davies KM, Chen TC,...
Am J Clin Nutr. 2003 Jan;77(1):204-10. Erratum in: Am J Clin Nutr. 2003 Nov;78(5):1047.
of season and latitude on the cutaneous synthesis of vitamin D3: exposure
to winter sunlight in Boston and Edmonton will not promote vitamin
D3 synthesis in human skin.
Webb AR, Kline L, Holick MF.
J Clin Endocrinol Metab. 1988 Aug;67(2):373-8.
- Sun exposure and mortality from melanoma.
Berwick M, Armstrong BK, Ben-Porat L, ...
J Natl Cancer Inst. 2005 Feb 2;97(3):195-9.