Vitamin D and Sun --> Re: Vitamin D and kids

April 12, 2010

Interesting discussion on how much Vitamin D the sun provides - even in Summer.

Not sure the below answers, but interesting stuff.

One website pointed out that even in sunny climes, some women may not get enough sun exposure...no matter how sunny the day.

http://en.wikipedia.org/wiki/Vitamin_D

A study of highly sun exposed (tanned) heathy young skateboarders and surfers in Hawaii found levels below the proposed higher minimum of 30 ng/ml in 51% of the subjects. The highest 25(OH)D concentration was around 60 ng/ml (150nmol/L).[36] A similar study in Hawaii found a range of (11–71 ng/mL) in a population with prolonged extensive skin exposure while as part of the same study Wisconsin breastfeeding mothers were given supplements. The range of circulating 25(OH)D levels in women in the supplementated group was from 12–77 ng/mL. It is noteworthy that the levels in the supplemented population in Wisconsin were higher than the sun exposed group in Hawaii (which again included surfers).[37]

This includes areas with abundant sun exposure, such as Hawaii and southern Arizona, where over 50% of inhabitants have 25(OH)D level of under 20 ng/ml.[72][73

^ Binkley, N; Novotny, R; Krueger, D; Kawahara, T; Daida, YG; Lensmeyer, G; Hollis, BW; Drezner, MK (2007). " Low vitamin D status despite abundant sun exposure " . The Journal of clinical endocrinology and metabolism 92 (6): 2130–5. doi:10.1210/jc.2006-2250. PMID 17426097.

J Am Acad Dermatol. 2010 Apr 2. [Epub ahead of print]

Estimated equivalency of vitamin D production from natural sun exposure versus oral vitamin D supplementation across seasons at two US latitudes.

Terushkin V, Bender A, Psaty EL, Engelsen O, Wang SQ, Halpern AC.

Memorial Sloan-Kettering Cancer Center, New York, New York.

Abstract

BACKGROUND: The relationship between oral vitamin D supplementation and cutaneous photosynthesis is not well understood.

OBJECTIVE: We sought to provide estimates of the equivalency of vitamin D production from natural sun exposure versus oral supplementation.

METHODS: Using the FastRT simulation tool, we determined sun exposure times needed to achieve serum vitamin D(3) concentrations equivalent to 400 or 1000 IU vitamin D for individuals of various Fitzpatrick skin types living in Miami, FL, and Boston, MA, during the months of January, April, July, and October.

RESULTS: Peak ultraviolet B irradiation for vitamin D synthesis occurs around 12 PM Eastern Standard Time (EST).

In Boston, MA, from April to October at 12 pm EST an individual with type III skin, with 25.5% of the body surface area exposed, would need to spend 3 to 8 minutes in the sun to synthesize 400 IU of vitamin D.

It is difficult to synthesize vitamin D during the winter in Boston, MA.

For all study months in Miami, FL, an individual with type III skin would need to spend 3 to 6 minutes at 12 pm EST to synthesize 400 IU.

Vitamin D synthesis occurs faster in individuals with lighter Fitzpatrick skin types.

The duration to attain 1000 IU of vitamin D is longer in all scenarios.

LIMITATIONS: Results of the computer model are only approximations. In addition, calculations were made based on the assumption that (1/4) of 1 minimal erythema dose directed at (1/4) body surface area is equal to 1000 IU of oral vitamin D.

CONCLUSIONS: Although it may be tempting to recommend intentional sun exposure based on our findings, it is difficult, if not impossible to titrate one's exposure. There are well-known detrimental side effects of ultraviolet irradiation. Therefore, oral supplementation remains the safest way for increasing vitamin D status.

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J Steroid Biochem Mol Biol. 2010 Mar 16. [Epub ahead of print]

Sun exposure questionnaire predicts circulating 25-hydroxyvitamin D concentrations in Caucasian hospital workers in southern Italy.

Hanwell HE, Vieth R, Cole DE, Scillitani A, Modoni S, Frusciante V, Ritrovato G, Chiodini I, Minisola S, Carnevale V.

Department of Nutritional Sciences, University of Toronto, Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Ontario, Canada M5G 1X5.

Abstract

INTRODUCTION: Recent sun exposure should correlate with circulating 25-hydroxyvitamin D [25(OH)D] due to ultraviolet B (UVB)-catalyzed cutaneous synthesis of vitamin D. METHODS: A Sun Exposure Score was calculated for healthy adults using a recall questionnaire assessing daily Time in Sun (<5min, 5-30min, >30min) and Skin Exposure (face/hands; face/hands and arms; face/hands and legs; and " bathing suit " ) for 1 week in each of the winter and summer (n=47 and 23, respectively; n=18 participated in both). Concentrations of 25(OH)D were measured by DiaSorin RIA on end-of-week sera. RESULTS: Mean serum 25(OH)D was higher in summer than winter (58.6+/-16.5nmol/L vs. 38.8+/-29.0nmol/L, respectively, P=0.003 unpaired). The calculated Sun Exposure Score correlated strongly with serum 25(OH)D during summer (Spearman's rho=0.59, P=0.003); based on the Pearson coefficient of determination, summer Sun Exposure Score explained 38% of the variability in summer serum 25(OH)D. The Sun Exposure Score did not correlate with 25(OH)D in the winter (rho=0.19, P=0.210). The summer correlation was largely explained by the Time in Sun (rho=0.58, P=0.004) rather than area of Skin Exposed (rho=0.10, P=0.660). Although there was a correlation between winter and summer Sun Exposure Scores (rho=0.63, P=0.005), there was no summer vs. winter correlation in serum 25(OH)D (rho=0.08, P=0.76).

CONCLUSION: This simple 1-week sun exposure recall questionnaire predicted summer serum 25(OH)D concentrations, accounting for 38% of the variability in 25(OH)D among healthy Italian adults.

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http://www.ajcn.org/cgi/reprint/67/6/1108.pdf

Locke, MD

>

> Hi Graham,

>

> My point is,

> I think the supposition that Vit D requirements can be completely filled by sun exposure is a complete falsehood whether today, 100 years ago or prehistory. As someone mentioned Vit D may not even be " strictly " a vitamin as our body can manufacture it. How about Nordic peoples, the Inuit nations, etc. I believe that dietary sources have always been a major source for them; probably from the cold water fish and the fowls and mammals that feed upon them, which are a majority of the diet in these largely non-agricultural societies.

> You replied,

> Some evidence would be nice. Taking the Amerindian as an example, what dietary source are you suggesting?

> and in a different email said,

> The RDA for Vitamin D used to be 400IU.

>

> Anyone know how that was reached?

>

> It's the amount of D3 in a teaspoon of cod liver oil .. ie. the minimum amount required to prevent rickets in children.

> Which I found funny because the 2 statements seem to confirm my point that above or below a certain latitude, and maybe at all latitudes, dietary VIt D is a more important source than skin production; and that cod (a cold water fish) liver oil is an excellent source.

> By the way, Rickets existed long before Whistler first described it in English in 1645, a bit before the industrial revolution. Check out:

> Vitamin D, Cod-Liver Oil, Sunlight, and Rickets: A Historical Perspective -- Rajakumar 112 (2): e132 -- Pediatrics

> To which Amerindians are you referring? The Inuit, as I already mentioned, or perhaps the Seneca, Apache, Sioux, Aztec, Mayan, Inca, Navaho, Anasazi, Penobscot, Shoshoni or Choctaw tribes?

> A couple of final points. One, I now feel that Vitamin D is correctly categorized as a vitamin because the majority of the human species needs a dietary source to maintain a healthy metabolic levels. Two, I wonder where the cod livers get all the Vitamin D?

> Sorry if I seem overly defensive,

> Straz

April 12, 2010

I didn't have time to read these papers, but read the abstract of the first.The surfers and skateboarders had an average age of 24, and sun exposure of 1.5 hours a week. That's hardly a lot.

I would suspect that the population included a significant number of asians and natives who tan more readily.Melanin preferentially absorbs UVB preventing D3 synthesis.Also the abstract doesn't say at what time of the day they had their sun exposure which is also important.

Also, if you look at skin reflectance, http://www.ncbi.nlm.nih.gov/pubmed/9453695

" Previous studies of human skin color have shown a strong relationship between skin color and distance from the equator, which has been interpreted as a link between skin color, latitude, and the intensity of ultraviolet radiation. The underlying assumptions are that UV radiation is greatest at the equator and that it diminishes with increasing latitude to the same extent in both the Northern and Southern Hemispheres. The standard analysis of human skin color is based on these assumptions, such that skin color is assumed to be darkest at the equator, and the decrease of skin color with latitude is assumed to be the same in both hemispheres. A nonlinear piecewise regression model was developed to test these assumptions and applied to mean skin reflectance data from 102 male samples and 65 female samples from across the Old World. For both males and females, skin reflectance (%) is lowest at the equator (darkest skin). Among males, skin reflectance increases roughly 8.2% for every 10 degrees of latitude in the Northern Hemisphere but only 3.3% for every 10 degrees of latitude in the Southern Hemisphere. Among females, the corresponding numbers are 8.1% in the Northern Hemisphere and 4.7% in the Southern Hemisphere. These results indicate that human skin color is darker in the Southern Hemisphere than in the Northern Hemisphere at equivalent latitude. Recent research shows that UV radiation is higher in the Southern Hemisphere than in the Northern Hemisphere at similar latitude. This difference, relating to astronomical and climatic conditions, may have existed in the past at different times and perhaps influenced the evolution of human skin color. "

Since the current scientific position is that man came from out of Africa, then the increase in skin reflectance the further one's ancestors lived away from the equalor is seen as an evolutionary pressure to absorb more UVB.