The effect of chronic caffeine administration on serum markers of bone mineral metabolism and bone histomorphometry in the rat.

Caffeine has been cited as a risk factor for osteoporosis in humans. In rats, caffeine increases calcium absorption and excretion and raises parathyroid hormone (iPTH) levels. This study investigated the effect of chronic caffeine administration on bone histomorphometry and serum markers of bone mineral metabolism. Twenty-seven male Sprague Dawley rats weighing approximately 300 g were divided into three groups: Group A (n = 8) served as controls, Group B (n = 9) received 2.5 mg/100 g caffeine in their drinking water, and Group C (n = 10) received 10 mg/100 g body weight caffeine in their drinking water. Animals were bled serially for the 8 week study period: Ionized calcium was measured from tail vein blood and serum iPTH and osteocalcin (BGP) from orbital sinus blood. All three groups received two doses of tetracycline for bone histomorphometry which was performed on a right tibial section from each animal. Ionized calcium was not different among the three groups at any time point. No alteration in serum iPTH levels was demonstrated except for day 56 when the high-dose group (C) showed a raised level (mean = 59.1, SE = +/- 8.9 pg/ml (P less than 0.05). By week 8 Group C showed a failure to gain weight compared with Group A. Group C mean weight = 384.0 +/- 6.6 g, Group A 427.4 +/- 10.8 g (P less than 0.005). Serum BGP was significantly increased in Group C compared with control (P less than 0.001). No differences in bone histomorphometry were observed among the three groups.(ABSTRACT TRUNCATED AT 250 WORDS)