And, of course, the mention of heart disease at higher levels (>90ng/ml, I believe) was important.
As pointed out vitamin D regulates calcium homeostasis. High doses of vitamin D are used in the VD(N) (vit D+nicotine) model to induce vascular calcification. I did not read the article, but I think I know what they were talking about. There was a study which showed very high vitamin D levels in "south Indian patients with ischemic heart disease"
Lastly, I must have missed it in other Vitamin D reading I've done, but the author points out that studies have shown that if you are getting Vitamin D from the sun, your body will shut down production after a point. However, if you are supplementing *and* getting it from the sun, your body will continue to produce as much as it would have if you hadn't been supplementing. This is important when going from winter to spring/summer if you are going to be exposed to more sun in the spring/summer months.
I guess so. The feedback only takes place in the skin, after some ten thousands of IUs are produced in the skin, further vitamin D is destroyed by the UV radiation
in your skin - so blood levels of 25(OH)D/supplemental cholecalciferol won't affect the feedback mechanism.
The other thing mentioned was that you can be on the same dose for months and your blood concentration may not increase, but after being on for years, it can. If true, that would seem to indicate some sort of change in the body after prolonged exposure to significant amounts of vitamin D.
Vitamin D metabolism is a mystery, sometimes.
The other mental note I'm making for myself is that you can go from a "good" level to "too high" in a short period of time as well, so if I'm going to supplement in the 2000+mg/day category, then I'm going to get tested every few months to be on the safe side. $240-$260/year seems like a reasonable cost to make sure I'm not over doing it. Of course, that adds up a bit if you count every member of the family.
Are you talking about vitamin D? (it is not measured in mg, btw)
Being too high is not an issue, it all depends on the chronic exposure. Having blood levels of 80-90ng/ml all year long, could be detrimental. (1) It's only one study, though.
Generally levels of >32ng/ml offer
very strong protection from heart disease.
(1) Eur J Epidemiol. 2001;17(6):567-71.
Serum 25-hydroxyvitamin D3 levels are elevated in South Indian patients with ischemic heart disease.
Rajasree S, Rajpal K, Kartha CC, Sarma PS, Kutty VR, Iyer CS, Girija G.
"When controlled for age and selected variables using the multivariate logistic regression, the adjusted OR relating elevated serum 25-hydroxyvitamin D3 levels (> or = 222.5 nmol/l, > or = 89 ng/ml) and IHD is 3.18 (95% CI: 1.31-7.73). "
Edit:
In a letter Reinhold Vieth questions their methodology, but even assuming that this result (which I have pointed out is an outlier) is irrelevant, there's no reason to go for such high levels (as there's zero proof of any benefits beyond 50ng/ml).
Edited by kismet, 10 March 2009 - 10:16 AM.