Vitamin D: newly discovered actions require reconsideration of physiologic requirements

Abstract

Vitamin D is not just for preventing rickets and osteomalacia. Recent findings in animal experiments, epidemiologic studies and clinical trials, indicate that adequate vitamin D levels are important for cancer prevention, controlling hormone levels, and regulating the immune response. Although 25 Hydroxyvitamin D (25OHD) levels above 10ng/ml may prevent rickets and osteomalacia, these levels are not sufficient to provide these more recently discovered clinical benefits. Rather, levels of 25OHD above 30ng/ml are generally recommended. Determining optimal levels of 25OHD and the amount of vitamin D supplementation required to achieve those levels for the numerous actions of vitamin D will only be established with additional trials. In this review, these newer applications are summarized and therapeutic considerations provided.

Effect of vitamin D status on clinical pregnancy rates following in vitro fertilization

“…6 Lower levels of vitamin D (< 75 nmol/L) have also been associated with a higher incidence of certain types of cancer and impaired immune response. 4,5 People living in countries at higher latitudes, such as the United States and Canada, are more prone to vitamin D insufficiency, especially during the winter months.7 Vitamin D insufficiency is highly prevalent in women of reproductive age.2,7 A Canadian study by Veith and colleagues 7 reported that 25.6% of nonwhite and 14.8% of white women of reproductive age (18-35 yr) had insufficient vitamin D levels (defined as < 40 nmol/L). Ozkan and colleagues 2 reported a 36% prevalence of vitamin D insufficiency (50-74 nmol/L) and a 27% prevalence of deficiency (< 50 nmol/L) among women of reproductive age with infertility.…”

“…Vitamin D is metabolized primarily in the liver to 25-hydroxy-vitamin D (25[OH]D), the serum concentration of which can be used as an indicator of vitamin D status. The classification of vitamin D status varies in the literature, 2,4,5 and because the relation between vitamin D and fertility has only recently been investigated, no specific cut-off values have been referenced in the literature. However, a Canadian guideline defined vitamin D deficiency as levels below 25 nmol/L, insufficiency as levels between 25 and 74 nmol/L, and sufficiency as levels of 75 nmol/L and greater.…”

“…6 Lower levels of vitamin D (< 75 nmol/L) have also been associated with a higher incidence of certain types of cancer and impaired immune response. 4,5 People living in countries at higher latitudes, such as the United States and Canada, are more prone to vitamin D insufficiency, especially during the winter months. 7 Vitamin D insufficiency is highly prevalent in women of reproductive age.…”

Vitamin D, leptin and impact on immune response to seasonal influenza A/H1N1 vaccine in older persons

“…Granzyme B is a surrogate marker for cytotoxic T cell response, and we found a weak positive correlation with change in granzyme B from Day 75 to Day 0, and 25-(OH) D. Vitamin D has been shown to encourage a Th2 skewed phenotype compared to Th1. 23,24 Replicating our finding involving granzyme B and studying vaccine-induced Th1-and Th2-like responses with relation to vitamin D is likely to be informative.…”

“…VDR is widely expressed in many tissues, including immune cells. 24,25 Importantly, the vitamin D level threshold that is relevant to its numerous non-skeletal actions has not been defined.…”