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/
m2; 6SD): 30.2 6 3.7] with 25-hydroxyvitamin D [25(OH)D] concentrations
,70 nmol/L during either WL or WM. All women were
given 10 mg vitamin D3/d and 1.2 g Ca/d and either weekly vitamin
D3 (375 mg) or a placebo equivalent to 63 mg (2500 IU)/d and 10 mg
(400 IU)/d, respectively. We measured TFCA with the use of dualstable
isotopes, 25(OH)D, parathyroid hormone, estradiol, calcitriol,
and urinary calcium at baseline and 6 wk in weight loss and vitamin
D3–supplementation (WL-D; n = 19), weight maintenance and vitamin
D3–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 6 1.1% of weight with no difference
between vitamin D3 supplementation and the placebo. The rise in
serum 25(OH)D was greatest in the WL-D group (19.8 6 14.5
nmol/L) compared with in WM-D (9.1 6 10.3 nmol/L) and placebo
groups (1.5 6 10.9 nmol/L). TFCA increased with vitamin D3
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 mg vitamin D/d is sufficient
to maintain the calcium balance.
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