Passive smoking linked to increased bone turnover in rats
MedWire News: Passive cigarette smoking is associated with increased bone turnover and decreased bone mineral density (BMD) in rats, Chinese researchers report.
"Many studies have identified smoking as a risk factor for osteoporosis, but it is unclear whether passive smoking has an effect on BMD and bone turnover and if such an effect could cause osteoporosis," remark Guang-hua Lei (Central South University, Changsha) and colleagues.
To address this, Lei and team exposed 24 female rats to sidestream cigarette smoke at a human equivalent of 30 cigarettes per day for 2, 3, or 4 months. They measured BMD and serum markers of bone turnover in each of the animals at the start and end of the study period and compared their findings with those from 24 unexposed control animals.
The researchers report in the journal BMC Musculoskeletal Disorders that there was no significant difference in BMD at the lumbar spine and femur between unexposed animals and those exposed to smoke for 2 or 3 months.
In contrast, 4 months of smoke exposure resulted in significant 11.8% and 10.5% decreases in BMD at the lumbar spine and femur, respectively, compared with controls.
Serum levels of the bone formation marker osteoclacin did not differ between the exposed and unexposed groups, regardless of the duration of exposure.
Levels of the bone formation marker bone-specific alkaline phosphatase, however, were a significant 17.5% and 37.8% lower in the 3-month and 4-month smoke-exposed rats, respectively, compared with controls.
In addition, levels of the bone resorption marker tartrate-resistant acid phosphatase 5b were a significant 53.9% and 59.4% higher in the 3-month and 4-month smoke-exposed rats, respectively, compared with controls.
At 4 months, the blood nicotine concentrations in smoke-exposed rats were 40.6 ng/ml, which is around that expected in heavy smokers.
But the researchers note that it is difficult to draw a direct comparison to smoking in humans, as humans inhale tobacco directly from cigarettes. "Thus, the model used in the present study reflected the effects of passive cigarette smoking, but not those of active smoking," they say.
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By Laura Dean