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 Lani 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
"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
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
"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
Burkman added that other scientists have shown a similar decline
in fertility among women who are heavy smokers.
Roxanne Mroz and MaryLou Bodziak, UB research associates,
contributed to this work, along with UB undergraduate students
Stuti Tambar, Brian Telesz, and Scott Beardsley.
The research was funded by the Philip Morris External Research
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