Re: Vitamin D deficiency may be responsible for cancer deaths
- From: "Noone Inparticular" <unreve89@xxxxxxxxxxx>
- Date: 28 Dec 2005 11:59:35 -0800
Dale wrote:
> "Lilith (Deanne Taylor)" <theoriste@xxxxxxxxx> wrote in message
> news:1135777622.056856.231100@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> > Another smoking gun for selection for lighter skin color?
> [...]
> > The study found that people in the north eastern U.S., and darker
> > skinned individuals, were at increased risk due to a lack of
> > sunshine-generated vitamin D.
>
> Doubtful, since cancer deaths usually occur long past the age when fertility
> begins. But there are fertility/survival-to-fertility related problems that
> arise from vitamin D deficiency and from folic acid breakdown, which is also
> related to UV exposure.
>
> http://anthro.palomar.edu/adapt/adapt_4.htm
> ----
> It would be harmful if melanin acted as a complete shield. A certain amount
> of shortwave ultraviolet radiation (UVB) must penetrate the outer skin layer
> in order for the body to produce vitamin D. Approximately 90% of this
> vitamin in people normally is synthesized in their skin and the kidneys from
> a cholesterol-like precursor chemical with the help of ultraviolet
> radiation. The remaining 10% comes from foods such as fatty fish and egg
> yolks. Simple vitamin D is converted by our bodies into two sequential
> forms. The last form, commonly referred to as vitamin D3, is needed for the
> intestines to absorb calcium and phosphorus from food for bone growth and
> repair. Calcium is also necessary in adults to maintain normal heart
> action, blood clotting, and a stable nervous system. However, too much
> ultraviolet radiation penetrating the skin may cause the break down of folic
> acid (or folate--one of the B vitamins) in the body, which can cause anemia.
> Pregnant women who are deficient in folic acid are at a higher risk of
> having babies with neural tube defects. Because folic acid is needed for
> DNA replication in dividing cells, its absence can have an effect on many
> body processes, including the production of sperm cells. It may be that the
> ability to produce melanin was selected for in our early human ancestors
> because it helped preserve the body's folic acid supply in addition to
> reducing the chances of developing skin cancer.
>
> People who live in far northern latitudes, where solar radiation is
> relatively weak most of the year, have an advantage if their skin has little
> shielding pigmentation. Nature selects for less melanin when ultraviolet
> radiation is weak. In such an environment, very dark skin is a disadvantage
> because it can prevent people from producing enough vitamin D, potentially
> resulting in rickets disease in children and osteoporosis in adults.
> Contributing to the development of osteoporosis in older people is the fact
> that their skin generally loses some of its ability to produce vitamin D.
> Women who had prolonged vitamin D deficiencies as girls have a higher
> incidence of pelvic deformities that prevent normal delivery of babies.
> ----
The connection between skin pigmentation, vitamin D3 (which is not
actually a vitamin; it is a steroid hormone) and evolution is not as
simple as it would appear. While it is true that blacks produce
significantly less Vitamin D3 than whites, there is no difference in
circulation 1,alpha-25dihydroxy-Vitamin D3, the business end of the
vitamin D metabolic pathway. It may be that the evolutionary
association of skin pigmentation with latitude isn't tied directly to
vitamin D3 production, as plausible as it seems.
"This [difference in vitamin D3 and 25 hydroxyvitamin D3 levels between
blacks and whites] then might be expected to have implications for
nutritional recommendations and guidelines of what are appropriate
vitamin D intakes for racial groups with extensive skin pigmentation.
However, this is apparently not necessary because Matsuoka et al
(13)clearly showed that there were differences in both vitamin D3 and
25-hydroxyvitamin D3 concentrations between blacks and whites, Harris
and Dawson-Hughes showed that there were differences in
25-hydroxyvitamin D3 concentrations between blacks and whites (their
Table 1), and *neither study showed significant differences in
circulating concentrations of 1a,25-dihydroxyvitamin D3 between backs
and whites*. Thus, as long as there are no unique biological responses
of 25-hydroxyvitamin D3 that cannot be supported by normal 1a,25-
dihydroxyvitamin D3 concentrations, then there may not be significant
adverse health consequences attributable to the lower concentrations of
25-hydroxyvitamin D3 when they are not below the range of 20-30
nmol/L."
(emphasis added)
See; AW Norman - Am J Clin Nutr 1998;67:1108-10.
(Available here with subscription;
http://www.ajcn.org/cgi/reprint/67/6/1108.pdf)
and accompanying paper;
SS Harris, B Dawson-Hughes Am J Clin Nutr 1998;67:1232-36
(Available here with subscription;
http://www.ajcn.org/cgi/reprint/67/6/1232.pdf)
.
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- Vitamin D deficiency may be responsible for cancer deaths
- From: Lilith (Deanne Taylor)
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- From: Dale
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