Vitamin D supplementation and calcium absorption during caloric restriction: a randomized double-blind trial.
What this study found
Vitamin D supplementation increased true fractional calcium absorption (TFCA), whereas caloric restriction and weight loss decreased TFCA. TFCA changed in the direction of higher absorption with vitamin D treatment (P<0.001) and lower absorption during weight loss (P<0.001). The authors concluded that when calcium intake was about 1.2 g/day, either a higher or lower vitamin D dose appeared sufficient to maintain calcium balance during caloric restriction. Serum 25(OH)D and 1,25(OH)2D3 did not predict TFCA, and no serious adverse events were reported.
- Study & population
- Randomized double-blind 6-week trial in postmenopausal women with overweight or obesity and low-to-moderate vitamin D status.
- Intervention
- Oral vitamin D3 was given in the active arms as 3 tablets weekly for 5 weeks, equivalent to about 2500 IU/day, taken with the largest meal of the day.
- Key limitation
- The active arms were small (WL-D n=19; WM-D n=20), and the intervention lasted only 6 weeks, limiting precision and long-term inference.
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Open PDFOriginal abstract
BACKGROUND Weight loss (WL) is associated with a decrease in calcium absorption and may be one mechanism that induces bone loss with weight reduction. OBJECTIVE Because vitamin D supplementation has been shown to increase true fractional calcium absorption (TFCA), the goal of this study was to examine the effect of vitamin D during WL or weight maintenance (WM). DESIGN A randomized, placebo-controlled, double-blind 6-wk study was conducted in 82 postmenopausal women [BMI (in kg/m(2); ±SD): 30.2 ± 3.7] with 25-hydroxyvitamin D [25(OH)D] concentrations <70 nmol/L during either WL or WM. All women were given 10 μg vitamin D(3)/d and 1.2 g Ca/d and either weekly vitamin D(3) (375 μg) or a placebo equivalent to 63 μg (2500 IU)/d and 10 μg (400 IU)/d, respectively. We measured TFCA with the use of dual-stable isotopes, 25(OH)D, parathyroid hormone, estradiol, calcitriol, and urinary calcium at baseline and 6 wk in weight loss and vitamin D(3)-supplementation (WL-D; n = 19), weight maintenance and vitamin D(3)-supplementation (WM-D; n = 20), weight loss and placebo (n = 22), and weight maintenance and placebo (n = 21) groups. RESULTS WL groups lost 3.8 ± 1.1% of weight with no difference between vitamin D(3) supplementation and the placebo. The rise in serum 25(OH)D was greatest in the WL-D group (19.8 ± 14.5 nmol/L) compared with in WM-D (9.1 ± 10.3 nmol/L) and placebo groups (1.5 ± 10.9 nmol/L). TFCA increased with vitamin D(3) supplementation compared with placebo treatment (P < 0.01) and decreased during WL compared with WM. Serum 25(OH)D or 1,25-dihyroxyvitamin D did not correlate with TFCA. CONCLUSION These data show that vitamin D supplementation increases TFCA and that WL decreases TFCA and suggest that, when calcium intake is 1.2 g/d, either 10 or 63 μg vitamin D/d is sufficient to maintain the calcium balance. This trial was registered at clinicaltrials.gov as NCT00473031.