Severe calcium deficiency increased visceral fat accumulation, down-regulating genes associated with fat oxidation, and increased insulin resistance while elevating serum parathyroid hormone in estrogen-deficient rats

Abstract

Menopause impairs calcium(Ca) metabolism and reduces bone mineral density (BMD), but the interaction of menopause with Ca deficiency in energy, glucose, lipid, and bone metabolism has not been studied. Herein we hypothesized that Ca deficiency at levels for post-menopausal women would impair energy, glucose, lipid, and bone metabolism in estrogen-deficient rats. This hypothesis was examined in ovariectomized (OVX) rats fed high-fat diets with different Ca levels for 12 weeks. OVX rats were allocated into either very low Ca (0.02%, VLCA), low Ca (0.7%, LCA), adequate Ca (1.18%, ACA, control), or excessive Ca (2.1%, EXCA). Sham-operated rats had the same diet as ACA (Normal-control). Ca intake was 37, 107, 190, and 311 mg/kg bw/d in the VLCA, LCA, ACA, and EXCA groups. The ACA group had higher serum parathyroid hormone concentrations than the Normal-control but were highest in VLCA. VLCA decreased BMD and lean body mass compared to ACA. Fasting serum glucose concentrations, even with higher serum insulin concentrations, were higher in the VLCA than ACA, indicating increased insulin resistance in VLCA. VLCA deteriorated glucose tolerance after oral glucose administration and impaired lipid profiles. LCA and EXCA had similar effects on metabolism as ACA, but LCA did not improve insulin sensitivity and lipid profiles as much as ACA. Expressions of hepatic genes related to fatty acid and cholesterol synthesis (FAS and SREBP-1c and HMGCR) were much higher in the VLCA than ACA and expressions of genes related fatty acid degradation(CPT1 and CYP7A1) were much lower in VLCA than ACA. In conclusion, we accepted the hypothesis. Very low Ca intake (350–400 mg/d as a human equivalent) exacerbated estrogen-deficiency-induced impairments of energy, glucose, and lipid metabolism by elevating serum parathyroid hormone levels and inducing visceral fat accumulation and insulin resistance in estrogen-deficient rats, but there was no added benefit of excessive Ca.