What is an optimal blood level of vitamin D?
Recent data have shown that along with vitamin D helping calcium to be absorbed by the body, it is important in muscle strength, insulin action, immune health and resistance to cancer. Doctors feel 25-Hydroxyvitamin D is the best way to evaluate vitamin D status. A typical
25-hydroxyvitamin D level is 40 nmol/l, which many scientists previously assumed to be adequate. Last year in an osteoporotic conference, experts said the optimal 25-hydroxyvitamin D level for most people is 75-80 nmol/l. When vitamin D levels are lower, parathyroid hormone concentrations in the blood rise and trigger excessive bone loss. People who are 70 years of age or older may need more than 100 nmol/l of vitamin D to hold parathyroid hormone at healthy concentrations. Low vitamin D levels may identify people at risk for type 2 diabetes as well as for bone problems. One study showed that increasing vitamin D levels from 25 nmol/l to 75 nmol/l would improve insulin sensitivity
by 60%, which is a greater increase than many antidiabetic medications. In another study of people over the age of 60, vitamin D levels of 40 nmol/l or less resulted in subjects walking more slowly and having more trouble rising from a chair than people with levels higher than 86 nmol/l. Women in the highest 25-hydroxyvitamin D levels (about 100 nmol/l) had about one-half the colorectal cancer risk of women in the lowest group at about 40 nmol/l.
Vitamin D supplementation reduces insulin resistance
In a randomized, placebo-controlled, double-blind study involving 81 insulin resistant South Asian women with vitamin D deficiency (serum 25(OH)D < 50 nmol/L), aged 23-68 years, results indicated that vitamin D supplementation may improve insulin resistance and insulin sensitivity. The women were randomized to 100 mug vitamin D3 (n=42) or placebo (n=39) for a period of 6 months. Significant improvements in insulin resistance and insulin resistivity were observed in the vitamin D supplemented group, compared with the placebo group, with optimal improvement associated with serum 25(OH)D levels >/= 80 nmol/L. Thus, the authors of this study conclude, “Improving vitamin D status in insulin resistant women resulted in improved IR and sensitivity, but no change in insulin secretion. Optimal vitamin D concentrations for reducing IR were shown to be 80-119 nmol/l, providing further evidence for an increase in the
recommended adequate levels.”
May reduce risk of acute respirator tract infections
In a prospective cohort study involving 198 healthy adults, higher concentrations of 25-hydroxvitamin D were found to be associated with a significantly reduced risk of acute respiratory tract infections. Specifically, having a 25(OH)D of 38 ng/ml or higher was associated with a 2-fold reduction in the risk of developing acute respiratory tract infections, and moreover, a marked reduction in the percentage of days ill. Higher 25(OH)D levels were found to be associated with vitamin D supplementation, lean body mass, and light skin pigmentation. The
authors conclude, “The findings of the present study provide direction for and call for future interventional studies examining the efficacy of vitamin D supplementation in reducing the incidence and severity of specific viral infections, including influenza, in the general population and in subpopulations with lower 25-hydroxyvitamin D concentrations, such as pregnant women, dark skinned individuals, and the obese.”
“Vitamin D: What’s Enough? Many People May Need Much More,” Raloff J, Science News, October 16, 2004;166:248-249.
Vitamin D supplementation reduces insulin resistance in South Asian women living in New Zealand who are insulin resistant and vitamin D deficient – a randomized, placebo-controlled trial, Von Hurst PR, Coad J, et al, Br J Nutr, 2009 Sep 28:1-7.
“Serum 25-hydroxyvitamin D and the incidence of acute viral respiratory tract infections in healthy adults,” Sabetta JR, Depetrillo P, et al, PLoS One, 2010 June 14; 5(6): e11088.