BACKGROUND Studies indicate that intake of vitamin D in the range from 1,100 to 4,000 IU/d and a serum 25-hydroxyvitamin D concentration [25(OH)D] from 60-80 ng/ml may be needed to reduce cancer risk. Few community-based studies allow estimation of the dose-response relationship between oral intake of vitamin D and corresponding serum 25(OH)D in the range above 1,000 IU/d. MATERIALS AND METHO...

OBJECTIVE To assess the relationship between circulating 25(OH)D, 1,25(OH)2D, and 24,25(OH)2D in pregnancy at term, and to test the hypothesis that serum 25(OH)D and 24,25(OH)2D are repressed by high serum 1,25(OH)2D levels. DESIGN Twenty studies in pregnant women at term and 14 studies in young non-pregnant women were selected from the electronic literature. From these studies the mean serum...

OBJECTIVE The main objective of the current study was to assess the distribution and its prognostic value of serum 25-hydroxyvitamin D (25[OH] D) levels assessed at admission in Chinese postmenopausal women with hip fracture. METHODS From January 1, 2012 to December 31, 2013, all postmenopausal women with first-ever hip fracture were recruited to participate in the study. Serum 25[OH] D level...

Bioactivation of vitamin D consists of two sequential hydroxylation steps to produce 1α,25-dihydroxyvitamin D3. It is clear that the second or 1α-hydroxylation step is carried out by a single enzyme, 25-hydroxyvitamin D 1α-hydroxylase CYP27B1. However, it is not certain what enzyme or enzymes are responsible for the initial 25-hydroxylation. An excellent case has been made for vitamin D 25-hydr...

The requirements for vitamin D were last set in 1997 by the Food and Nutrition Board of the Institute of Medicine. Intakes were assumed to come from diet, and values were based on achievement of adequate vitamin D status and on observed values to prevent seasonal variations in parathyroid hormone concentrations. Serum 25-hydroxyvitamin D concentrations were considered the best indicator of vita...

On a population basis, there is a gradual decline in vitamin D status (plasma 25(OH)D) throughout winter. We developed a mathematical model to predict the population winter plasma 25(OH)D concentration longitudinally, using age-specific values for 25(OH)D expenditure (25(OH)D3t1/2), cross-sectional plasma 25(OH)D concentration and vitamin D intake (VDI) data from older (70+ years; n=492) and yo...

Methods The measurements of UVB radiation energy were obtained using UV spectrometer at different times of the day between 9 am and 4 pm, in different seasons. The instrument was calibrated to denote 13 microWatt/ cm2 of irradiance per mVolt of deflection. Measurements were taken at our institution (situated in the countryside), at crowded inner city areas and the villages where our subjects re...

OBJECTIVE To determine the association between 25-hydroxyvitamin D (25-OHD) concentration and risk of incident type 2 diabetes. RESEARCH DESIGN AND METHODS In a nested case-control study conducted among 608 women with newly diagnosed type 2 diabetes and 559 control subjects in the Nurses' Health Study, we measured the association between baseline plasma 25-OHD concentration and risk of incide...

OBJECTIVE To confirm previous evidence suggesting an association between autism and low vitamin D serum levels. METHODS This preliminary exploratory study assessed the circulating levels of 25-hydroxyvitamin D (25-OHD) in pediatric patients with autism and in typically developing controls from Juiz de Fora, Brazil. RESULTS Serum levels of 25-OHD were lower in children with autism (26.48 ± 3...

The effect of high doses of 25-hydroxycholecalciferol on plasma calcium concentration was studied in rats receiving a low-calcium normal vitamin D diet. In bilaterally nephrectomized animals, as in sham-operated controls, 62.5 nmol of 25-hyroxycholecalciferol did not produce a rise of plasma calcium concentration. In contrast, the administration of 125 or 625 nmol, doses 1,000-5,000 times the m...