WCO: Second-Hand Smoke Is A Bone-Breaker

TORONTO June 7 ? Second-hand smoke can boost the risk of osteoporosis in pre-menopausal women, researchers reported here.

In a large Chinese cohort, pre-menopausal non-smoking women exposed to second-hand smoke had nearly triple the risk of osteoporosis as women who weren't exposed and 2.5 times the risk of non-vertebral fracture, according to Mary Bouxsein, Ph.D., of Beth Israel Deaconess Medical Center in Boston.

The effects in men were similar, but the numbers are less reliable because few of the men in the study were non-smokers. Dr. Bouxsein reported at the World Congress on Osteoporosis here.

It is well known, she said, that smoking itself is bad for the bones. A 2000 study showed that smokers lose bone mineral density at the rate of about 5.4% a year and a large meta-analysis published last year showed that smokers have 1.6 times the risk of hip fracture, even after adjusting for bone mineral density in the femoral neck.

Also, several new studies presented here quantified the risk of smoking, she said.

"Clearly, smoking is not good for skeletal health," Dr. Bouxsein said, "but the impact of second-hand smoke on skeletal health had not yet been studied."

To fill that gap, she and colleagues studied 7,137 men and 6,833 women in Anhui province in China. Of the women, 4,585 were pre-menopausal and 2,248 were post-menopausal, although Dr. Bouxsein pointed out that the whole cohort - including the post-menopausal women - was relatively young.

"This is a cohort we hope to follow longitudinally," she said.

The researchers collected smoking and fracture history through interviews and took bone mineral density measurements for the hip, spine, and total body. More than 80% of the men were current smokers, she said, and less than 10% of the women. So about 80% of the women were exposed to second-hand smoke.

Analysis found:

• Pre-menopausal women exposed to second-hand smoke had a 2.7-fold increase in the risk of osteoporosis (defined as low bone mineral density at the hip) compared with those without exposure. The 95% confidence interval ranged from 1.1 to 6.7.
• The same group had a 2.5-fold increased risk of non-vertebral fracture compared to those without exposure. The 95% confidence interval ranged from 1.1 to 6.5.
• There was no significant association seen in post-menopausal women, suggesting the predominant effect of estrogen deficiency because the women were relatively young and on average only about six years post-menopause.
• Compared with smokers without second-hand smoking exposure, male smokers with higher second-hand smoking had a 1.8-fold higher risk of having osteoporosis (95% CI: 1.1-3.2).

The finding is "biologically plausible," because one effect of cigarette smoke is to lower estrogen levels, she said.

But the effects of cigarette smoke are not limited to the elderly, according to Mattias Lorentzon, M.D., Ph.D., of Gothenburg University in Sweden. Dr. Lorentzon and colleagues looked at bone mineral density in more than 1,000 Swedish men between the ages of 18 and 20, as part of a study following their health.

Using computer-assisted tomography, the researchers found that smokers had lower bone density than their peers, mainly in the hip, where the smokers were in general 5% lower. The technique allowed the researchers to pinpoint the loss of bone to the cortical bone - the stiff outer layer surrounding the spongy trabecular bone - which was thinner in smokers.

The effect of smoking on the bone health of young people has been controversial, Dr. Lorentzon said. "Now, we clearly demonstrate the young smokers also have significant losses in bone density," he said.