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Sunshine is the most important source of vitamin D - the UV rays in sunshine trigger the synthesis in our skin.
Vitamin D is now being touted as a vitamin capable of reducing cancer rates by as much as 60 - 70%, following rigorous scientific studies.
Improve your food sources of vitamin D. Be aware that this is a "supplement" and not a "substitute" for sunshine though, as it is generally not possible to get enough amounts of vitamin D through food alone. There are two possible food sources, namely foods that have been fortified with vitamin D during the manufacturing process and foods that contain vitamin D naturally:
* Fortified foods are usually milk and breakfast cereals. Read the nutrition labels to see if vitamin D has been added.
* The best source of food vitamin D is found in fish. Salmon, mackerel, tuna, and sardines are excellent sources. If you can stomach it, cod liver oil is also a good source.
* Egg yolks, margarine, cheese, and beef liver also have small amounts of vitamin D
A recent review of 45 vitamin D studies conducted by the Cochrane Collaboration Vitamin D and vitamin D analogues for preventing fractures associated with involutional and post-menopausal osteoporosis.
ReplyDelete"Overall there is a small but significant increase in gastrointestinal symptoms and renal disease associated with vitamin D or its analogues. "
None of the healthy controls in the NCI cancer study had vitamin D concentrations over 31.25 ng/ml .
Vieth and like minded researchers all sound very plausible but what they consider to be a optimal vitamin D level is naturally attained by virtually nobody apart from a minority of Hawiian lifeguards. By nobody I don't just mean in the US, I mean nobody on earth. People whose evolution has been in tropical regions of the world have adapted to the year round intense sunlight they are exposed to and it is clear that involves having low vitamin D levels. For example a review of vitamin D in Africa (Here) gives the median levels of 26 ng/ml for the equatorial countries Kenya and Congo. There is now solid evidence to support the idea of this genetic tendency to low vitamin D levels in those of tropical ancestry. Blood vitamin D levels in relation to genetic estimation of African ancestry
"The effect of high vitamin D exposure from sunlight and diet was 46% lower among African Americans with high African ancestry than among those with low/medium ancestry. Conclusions: We found novel evidence that the level of African ancestry may play a role in clinical vitamin D status"
I'm sure other populations which evolved in intense sunlight are much the same. In a study from south India,” (High prevalence of vitamin D deficiency in healthy south Indians) levels below 20ng/ml were found in 44% of the men and 70% of the women yet they got a lot of sun. The subjects are described as “agricultural workers starting their day at 0800 and working outdoors until 1700 with their face, chest, back, legs, arms, and forearms exposed to sunlight"
In (Hollis et al 2007) even "Honolulu, Hawaii volunteers with a self-reported sun exposure time of three or more hours per day on five or more days per week for at least the preceding three months exhibited a wide range of circulating circulating vitamin D levels (11–71 ng/mL).
I don't understand why anyone would think levels of D found in a minority of surfers with massive sun exposure (year round UV exposure that no ancestral European ever got ) is perfect. Most subjects never got near 60 ng/ml and that is clearly not due to lack of sun, ithe majority of people are naturally selected NOT to reach double the average of normal healthy people (31ng/m l ) by sun exposure. For example "Europeans are genetically polymorphic in their ability to maintain blood levels of vitamin D. At least two alleles reduce the effectiveness of the vitamin-D binding protein, and their homozygotes account for 9% and 18% of French Canadians (Sinotte et al., 2009)". (Sinotte et al 2009)
Hollis (2007 investigated two separate populations: the first, (discussed above) individuals from Hawaii who received significant sun exposure; the second, subjects from a lactation study who received up to 6,400 IU vitamin D3/day for six months. "the range of circulating 25(OH)D levels in women in the supplementation group was from 12–77 ng/mL"
Yikes! they went higher than the extremely sun exposed Hawaii subjects on a mere 6,400 IU. What is even more worrying is that many did not; if they were trying to attain the perfect level of 63ng/ml these women would indeed have to take 10,000 IU. Where is the harm in that ? Well, ingested vitamin D is not the same as skin synthesised D Human plasma transport of vitamin D after its endogenous synthesis says
ReplyDelete"These findings indicate that endogenously synthesized vitamin D3 travels in plasma almost exclusively on DBP, providing for a slower hepatic delivery of the vitamin D and the more sustained increase in plasma 25-hydroxycholecalciferol observed after depot, parenteral administration of vitamin D. In contrast, the association of orally administered vitamin D with chylomicrons and lipoproteins allows for receptor-mediated, rapid hepatic delivery of vitamin D, and the reported rapid but less-sustained increases in plasma 25-hydroxycholecalciferol".
So supplementation is not handled in the same way; ingestion of vitamin D is not really the same. Is there any reason to think 10,000IU of D sloshing through the circulation will do harm ? Yes. Vitamin D and osteogenic differentiation in the artery wall
"There is some evidence to suggest that dietary vitamin D may be carried by lipoprotein particles into cells of the artery wall and atherosclerotic plaque, where it may be converted to active form by monocyte-macrophages. These findings raise interesting questions regarding the effects of vitamin D intake on atherosclerotic calcification and cardiovascular risk.”
Since that was written Vitamin D, Adiposity, and Calcified Atherosclerotic Plaque in African-Americanshas demonstrated positive associations between 25-hydroxyvitamin D and aorta and carotid artery CP in African-Americans.