Bone Abstracts

Caffeine, a methylxanthine present in coffee, tea, coca-cola and other beverages, is considered to be responsible for an increased risk of osteoporosis in coffee drinkers, however the data from human and experimental studies are inconsistent. The aim of this study was to investigate the effects of a moderate dose of caffeine on the skeletal system of rats with normal and decreased estrogen level (developing osteoporosis due to estrogen deficiency).

Caffeine (20 mg/kg p.o. daily) was administered for 4 weeks to non-ovariectomized and bilaterally ovariectomized mature Wistar rats, and its effects were compared with appropriate controls (n=10 per group). The ovariectomy was performed 7–8 days before the start of caffeine administration, under ketamine–xylazine anesthesia. Bone mass, mass of bone mineral, calcium and phosphorus content, histomorphometric parameters, serum bone turnover markers (RatLaps and osteocalcin), and mechanical properties of the tibial metaphysis and femoral diaphysis (in three-point bending tests) and the femoral neck (in a compression test) were examined.

Caffeine favorably affected the skeletal system of the ovariectomized rats, slightly inhibiting development of bone changes induced by estrogen deficiency (increasing bone mineralization, and improving the strength and structure of cancellous bone). Moreover, caffeine favorably affected mechanical properties of compact bone. There were no significant effects of caffeine in rats with normal estrogen level, however two-way ANOVA revealed significant main effects of caffeine, indicating increased bone strength regardless of the estrogen status. It may be speculated that the favorable caffeine effects were mediated via blockade of A₁ adenosine receptors, known to be involved in regulation of bone resorption.

In conclusion, results of this study indicate that moderate caffeine intake may be safe and even exert some beneficial effects on the skeletal system.