Men who smoke cigarettes may experience a significant decline in their capacity to father a child, research by a reproductive medicine specialist from the University at Buffalo has shown.
Sperm from nearly two-thirds of the chronic smokers in the study failed a special test that measures the ability of sperm to fertilize an egg. On average, those men showed a 75 percent decline in fertilizing capacity when compared to nonsmokers. Lead researcher Loni Burkman, Ph.D., presented the results today (Oct. 17, 2005) at the <<>> annual meeting in Montreal, Quebec.
Burkman is associate professor and head of the Section on Andrology, Department of Gynecology and Obstetrics in the UB School of Medicine and Biomedical Sciences and an assistant professor of urology.
"Like other cells in the body, human sperm carry a receptor for nicotine, which means they recognize and respond to nicotine," said Burkman. "This happens because nicotine from tobacco mimics one of the most important neurochemicals produced in the body. "Using sperm of nonsmokers, we reported previously that the addition of nicotine changed three sperm functions required to fertilize an egg.
"In this new study, we examined whether sperm from chronic tobacco smokers are defective in binding to the zona, the cover surrounding an egg," said Burkman. "Our results could mean that heavy smoking overloads the nicotine receptor in human sperm and in the testes, leading to a decline in fertilizing potential."
The study involved 18 men who reported smoking at least four cigarettes a day, every day, for more than two years. On average, these men had smoked for about 15 years. Their sperm function was compared to that of non-smoking donors who served as controls and whose fertilizing capacity had been confirmed.
Using a test called the Hemizona Assay developed by Burkman, the researchers cut a zona in half, placing one half with a smoker's sperm and the matching half with control sperm. After two to three hours of incubation, researchers counted the number of sperm attached tightly to the outside of each half.
The number of attached sperm from the smoker was compared to the control number, which gave a ratio or index. The Hemizona Assay has been shown to predict fertilization failure during in vitro fertilization.
"To fail, the index must be less than 65, meaning that the smoker's sperm had less than 65 percent of the fertilizing capacity found in the donor," Burkman said. "An index below 36 identifies a severe loss in fertilizing capacity."