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Monday 24th October, 2005
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Men who smoke may experience a significant decline in
fertility, research at the University at Buffalo has shown.
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BUFFALO, N.Y. -- 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 American
Society of Reproductive Medicine 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.
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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."
Results showed that the sperm from almost two-thirds of the smokers
failed the test, while the remainder showed normal function. Almost all
the smokers whose sperm failed the test had an index of 36 or less, with
an average of 25.
"None of these men had a zero fertilizing potential," said Burkman,
"but the results mean that their sperm had only 25 percent of the
fertilizing function found in nonsmoking men. The data also showed that
the men who failed were smoking about twice as many cigarettes per day,
an average of 19 per day, compared to the smokers who passed the assay."
As another way to understand the impact of smoking, the researchers
calculated a "smoking load" for each smoker by multiplying the number of
cigarettes smoked per day by the number of years smoked. The load varied
from 16 to 750 for the 18 men.
Results showed that the men who smoked fewer cigarettes for fewer
years had smaller smoking loads, ranging from 16 to 200. In this group,
71 percent passed the Hemizona Assay, indicating normal fertility. The
remaining men had a high smoking load, and only 18 percent passed the
assay.
"Specialized testing clearly reveals a significant drop in fertility
potential for men who are heavy tobacco smokers," said Burkman. "Smoking
men also should be aware that smoking can damage their sperm DNA,
passing on faulty DNA to their baby. Concerned smokers should quit or be
tested in a local andrology laboratory."
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Citation: Fertility and Sterility, Vol. 84, No. 2, 325-530 (August
2005).
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