Effects of caffeine on the bones of aged, ovariectomized rats

Caffeine is a substance which many people consume in their daily life. Caff eine's effects on bone are still controversial. Using ovariectomized rats, the present study was conducted to determine to what extent caffeine intake affects the mechanical properties, bone minerals and histology. Aged rats were divided into 2 groups after ovariectomy. Group 1 was fed a 20% protein diet as a control, and group 2 was fed a 20% protein diet supplemented wit h caffeine (2 mg/100 g body weight). The respective diets were fed to the r ats of each group for 90 days. Rats were then killed by heart puncture, blo od was collected, and femurs were removed. In 1 group of femurs paraffin cr oss-sections were made at the midshaft of each bone. Total width, cortical width, total cross-sectional bone area of the midshaft, and the number of o steocytes in randomly selected areas were measured. Another group of bones was subjected to three-point bending testing until failure. Bones were then pulverized and Ca, P, Mg, Zn, Sr, Si, hydroxyproline and hexosamine conten ts and crystallite size were measured. Various mechanical properties, excep t modulus of elasticity, in the caffeine group were consistently 7-23% lowe r than the noncaffeine controls. Yield strain in the caffeine group was sig nificantly less than in the noncaffeine controls. Zinc, Sr, and crystallite size of bone showed a significant decrease in the caffeine group, whereas Si contents significantly increased. Our current results indicate that rout ine intake of caffeine in the elderly should be regarded with some caution.