High vitamin D and calcium intakes increase bone mineral (Ca and P) content in high-fat diet-induced obese mice

Vitamin D and calcium are essential for bone formation, mineralization, and remodeling. Recent studies demonstrated that an increased body mass can be detrimental to bone health. However, whether an increase in dietary vitamin D and calcium intakes in obesity is beneficial to bone health has not been established. The aim of this study was to examine the effects of increased vitamin D and calcium intakes, alone or in combination, on bone status in a high-fat diet-induced obesity (DIO) mouse model. We hypothesized that DIO in growing mice affects bone mineral status and that high vitamin D and calcium intakes will promote mineralization of the growing bone in obesity via Ca²⁺ regulatory hormones, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and parathyroid hormone (PTH). Male mice were fed high vitamin D3 (10 000 IU/kg), high calcium (1.2%), or high vitamin D3 plus high-calcium diets containing 60% energy as fat for 10 weeks. Bone weight, specific gravity, mineral (Ca and P), and collagen (hydroxyproline) content were measured in the femur and the tibia. Regulators of Ca²⁺ metabolism and markers of bone status (PTH, 25-hydroxyvitamin D [25(OH)D], 1,25(OH)2D3, and osteocalcin) were measured in blood plasma. Diet-induced obese mice exhibited lower bone Ca and P content and relative bone weight compared with the normal-fat control mice, whereas collagen (hydroxyproline) content was not different between the two groups. High vitamin D3 and calcium intakes significantly increased bone Ca and P content and relative bone weight in DIO mice, which was accompanied by an increase in 1,25(OH)2D3 and a decrease in PTH and osteocalcin concentrations in blood. The findings obtained indicate that increased vitamin D and calcium intakes are effective in increasing mineral (Ca and P) content in the growing bone of obese mice and that the hormonal mechanism of this effect may involve the vitamin D–PTH axis.