Calcium and vitamin D intake maintained from preovariectomy independently affect calcium metabolism and bone properties in Sprague Dawley rats.

Abstract

The interaction of habitual Ca and vitamin D intake from preovariectomy to 4months postovariectomy on bone and Ca metabolism was assessed. Higher Ca intake suppressed net bone turnover, and both nutrients independently benefitted trabecular structure. Habitual intake of adequate Ca and ~50nmol/L vitamin D status is most beneficial. Dietary strategies to benefit bone are typically tested prior to or after menopause but not through menopause transition. We investigated the interaction of Ca and vitamin D status on Ca absorption, bone remodeling, Ca kinetics, and bone strength as rats transitioned through estrogen deficiency. Sprague Dawley rats were randomized at 8weeks to 0.2 or 1.0% Ca and 50, 100, or 1,000IU (1.25, 2.5, or 25μg) vitamin D/kg diet (2 × 3 factorial design) and ovariectomized at 12weeks. Urinary (45)Ca excretion from deep-labeled bone was used to assess net bone turnover weekly. Ca kinetics was performed between 25 and 28weeks. Rats were killed at 29weeks. Femoral and tibiae structure (by μCT), dynamic histomorphometry, and bone Ca content were assessed. Mean 25(OH)D for rats on the 50, 100, 1,000IU vitamin D/kg diet were 32, 54, and 175nmol/L, respectively. Higher Ca intake ameliorated net bone turnover, reduced fractional Ca absorption and bone resorption, and increased net Ca absorption. Tibial and femoral trabecular structures were enhanced independently by higher Ca and vitamin D intake. Tibial bone width and fracture resistance were enhanced by higher vitamin D intake. Dynamic histomorphometry in the tibia was not affected by either nutrient. A Ca × vitamin D interaction existed in femur length, tibial Ca content, and mass of the soft tissue/extracellular fluid compartment. Adequate Ca intake and serum 25(OH)D level of 50nmol/L provided the most benefit for bone health, mostly through independent effects of Ca and vitamin D.