The effect of calcium intake and vitamin D status on calcium and bone metabolism in females during growth and postmenopause
Abstract
Adequate intake of calcium and vitamin D are known to benefit bone health in neonates and adults. However, recent observations have suggested that vitamin D status, or serum 25-hydroxyvitamin D (25(OH)D), is not a major regulator of calcium utilization in adolescents. We investigated the effect of supplementing 1000 IU vitamin D/day on calcium balance and fractional calcium absorption in a cross-over design in 11 adolescent girls. Vitamin D status, fractional calcium absorption, and calcium retention were the primary outcome measures. Vitamin D status improved with supplementation. Vitamin D supplementation did not significantly affect net calcium absorption nor retention. However, fractional calcium absorption decreased with vitamin D supplementation. Thus, higher vitamin D status is may not benefit vitamin D-induced fractional Ca absorption in healthy adolescents in the United States. Calcium and vitamin D are interdependent nutrients and should be considered together for calcium homeostasis. We studied the interaction of calcium and vitamin D in female Sprague-Dawley rats during adulthood through estrogen deficiency in a 2 x 3 factorial design. Treatment diets containing either 0.2% or 1.0% calcium and 50, 100, or 1000 IU /kg diet were provided at 8 weeks of age through 4 months post-ovariectomy (OVX; OVX at 12 weeks of age). Continuous monitoring of bone balance through the appearance of bone tracer in urine revealed a protective effect of calcium after estrogen deficiency. An interaction of these 2 nutrients was observed in femoral length and tibial calcium content. Both calcium and vitamin D intake increased endogenous calcium secretion, trabecular bone, and femur width in an independent manner. Calcium intake additionally increased total calcium absorption and decreased bone resorption. Thus, these two nutrients affect both calcium absorption and bone structure, but high calcium and vitamin D status of 50 nmol/L (vitamin D intake 100 IU/kg diet) was optimal for most bone health indicators. In conclusion, vitamin D affects calcium metabolism differently according to life stage and calcium intake. Our results indicate that vitamin D supplementation may not improve Ca absorption during growth or as long as Ca intake is adequate. However, vitamin D may protect bone by affecting the structure of trabecular bone and bone width. High calcium intake may alleviate bone resorption after menopause, regardless of vitamin D status. Future research is required to study the effect of sex and other dietary factors, such as phosphorus, on the interaction of calcium and vitamin D in a dose dependant manner.
Degree
Ph.D.
Advisors
Weaver, Purdue University.
Subject Area
Nutrition
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