The effects of age and dietary restriction without nutritional supplementation on whole bone structural properties in C57BL/6J mice.
While caloric restriction is a proven means to extend longevity, its effects on bone are not well understood. This study examined the effects of dietary restriction without vitamin or mineral supplementation on bone in female 60- and 120-day-old C57BL/6J mice. Baseline controls were sacrificed at 60 or 120 days, while diet-restricted animals ate approximately 72.9-78.6% of the ad libitum fed animals for thirty days. 60-day-old ad libitum animals experienced normal growth with average increases of 6.4% in bone length, 23.5% in bone mass, 9.4% in %mineralization, 36.4% in maximum strength, 59.2% in stiffness, 22.3% in cortical thickness, 12.9% in %cortical area, and 11.3% in microhardness. Growth in 120-day-old ad libitum animals followed a trend but with more modest increases. Diet-restricted mice matured very little from baseline levels in 60-day-old animals. There were no significant changes from baseline levels in the parameters indicated above, except for a 8.3% decrease in %cortical area attributable to increased resorption. 120-day-old diet-restricted animals also evidenced little deviation from baseline levels except for significant decreases in %mineralization (2.1%) and %cortical area (6.7%). The effects of diet restriction on bone properties decreased with age. Bone from 60-day-old diet-restricted mice showed diminished mechanical and compositional properties, resulting from little growth and excess resorption. Bone from 120-day-old diet-restricted mice showed little growth and some resorption. Increased resorption, localized on the endosteal surfaces, likely minimized the negative impact of structural degradation of the long bones. Resorption may have also provided minerals to compensate for nutritional deficiencies.