Seasonal variations in vitamin D status and calcium absorption do not influence bone turnover in young women

Abstract

Objective: To evaluate the effect of seasonal variations in UV B-exposure on calcium absorption and bone turnover in young women with the overall goal to assess the potential bene®t of a vitamin D supplementation during wintertime. Design: Cross-sectional study. Setting: Area of Bonn, Germany (51 N). Subjects: Thirty-eight women (24.5 AE 0.5 y) studied in winter and 38 females of the same age (24.7 AE 0.4 y) studied in summer. Results: As estimated by a 4 d food record, both groups had similar dietary calcium and phosphorus intakes (b1200 mgad, respectively) covering actual recommendations. Signi®cant reductions in serum concentrations of 25-hydroxyvitamin D (25OHD) and calcitriol, fractional calcium absorption (Fc 220 , measured by means of a stable strontium test), 24 h urinary calcium and 24 h urinary phosphorus excretion were observed during wintertime. 25OHD but not calcitriol was correlated with Fc 220 values and with 24 h urinary phosphorus excretion. Moreover, Fc 220 was related to 24 h urinary calcium excretion. Fasting 2 h-urinary deoxypyridinoline concentrations (biomarker of bone resorption) and serum levels of carboxyterminal propeptide of type I procollagen (biomarker of bone formation) showed no differences between summer and winter. Conclusions: Our data indicate a decrease in intestinal calcium and phosphorus absorption during wintertime, most likely because of a reduction in serum 25OHD levels. Since bone turnover was not affected by the seasonal differences in mineral metabolism, there is no objective for young women with high calcium intake to supplement vitamin D during wintertime.

Effect of vitamin D supplementation on vitamin D status and bone turnover markers in young adults

“…A study conducted in postmenopausal women corroborates these findings, reporting no correlation between 25(OH)D and PTH at physiological concentrations (Villareal et al, 1991). Vitamin D only plays a role in the synthesis of PTH, whereas the secretion of the hormone is regulated primarily by calcium (Pepe et al, 2005;Zittermann et al, 1998). We speculate that no change in PTH concentrations was observed in this study as subjects had adequate dietary intakes of calcium, before supplementation with another 1500 mg calcium/day and were not severely deficient in vitamin D.…”

Factors affecting newborn bone mineral content:in uteroeffects on newborn bone mineralization

“…Biochemical and hormonal markers of bone metabolism vary significantly (P < 0·05) according to the season, consistent with an acceleration of bone turnover and possible subclinical vitamin D deficiency in winter (Woitge et al 1998). In young women a reduction in serum 25-OHD was associated with decreased intestinal Ca and P absorption during wintertime, but was not associated with the changes in bone turnover markers (serum carboxy-terminal propeptide of type I procollagen (PICP) and urinary deoxypyridinoline; Zittermann et al 1998). …”

Combined calcium and vitamin D supplementation is not superior to calcium supplementation alone in improving disturbed bone metabolism in patients with congestive heart failure

“…However, earlier results have also demonstrated that a rise in serum 25(OH)D from 30 to 70 nmol/l had no beneficial effects on biomarkers of bone metabolism if subjects had a recommended daily calcium intake. In this case, the surplus of absorbed calcium was at least in part excreted in the urine (Zittermann et al, 1998). Since both, an increase in oral calcium intake and higher serum 25(OH)D levels result in a rise of intestinal absorbed calcium, calcium and vitamin D can obviously replace each other relative to their effects on calcium supply and calcium-mediated bone turnover.…”