But the impact of smoking on sex hormone levels in older women has been unclear.
Postmenopausal women in the study who smoked had much higher levels of both male and female sex hormones than women who had never smoked or women who had given up cigarette smoking.
The findings could help explain how smoking influences the risk for disease in older women, study researcher Judith Brand, MSc, of the Netherlands' University Medical Center Utrecht, tells WebMD.
"Apart from the known toxic and carcinogenic effects of cigarettes, smoking appears to also influence the risk for chronic disease by changing hormone levels," she says.
Tracking Hormone Levels
The study included 2,030 postmenopausal women between the ages of 55 and 81 (average age 65) who were grouped as current smokers, former smokers, or never smokers.
Blood samples were taken from all the study participants and sex hormone levels were analyzed.
Compared to nonsmokers, current smokers had higher overall levels of multiple male hormones such as testosterone. They also had higher estrogen levels -- a finding that has not been seen in many earlier studies, Brand says.
In fact, many previous studies have found that smoking causes estrogen levels to drop.
Sex hormone levels were highest for the heaviest smokers in the study. But women who had stopped smoking within one to two years of entry had levels that were similar to women who had never smoked.
"Obviously, quitting smoking has major health benefits such as prevention of cancer, respiratory disease, and heart disease," Brand says. He adds that smoking cessation may have additional benefits by modifying hormone-related disease risk.
The study appears this week in the Journal of Clinical Endocrinology & Metabolism.
Smoking's Risks Well Known
Endocrinologist Stuart Weinerman, MD, calls the findings interesting, but he remains unconvinced that smoking raises estrogen levels.
Weinerman is chief of the division of endocrinology at the North Shore-Long Island Jewish Health System in New Hyde Park, N.Y.
He tells WebMD that studies that are based on associations like this one "can really only raise questions. They can't answer them."
Even if the association is confirmed, Weinerman says the clinical relevance would be minimal.
"Given that the risk of smoking is so great, its impact on hormone levels probably doesn't have a tremendous impact," he says. "If smoking is the 800-pound gorilla, [smoking-related] hormone increases are more like a tiny flea."