Men who smoke cigarettes may experience a significant declinein their capacity to father a child, research by a reproductivemedicine specialist from the University at Buffalo has shown.
Spermfrom nearly two-thirds of the chronic smokers in the study failed aspecial test that measures the ability of sperm to fertilize an egg. Onaverage, those men showed a 75 percent decline in fertilizing capacitywhen compared to nonsmokers.
Lead researcher Loni Burkman, Ph.D.,presented the results today (Oct. 17, 2005) at the American Society ofReproductive Medicine annual meeting in Montreal, Quebec.
Burkmanis associate professor and head of the Section on Andrology, Departmentof Gynecology and Obstetrics in the UB School of Medicine andBiomedical Sciences and an assistant professor of urology.
"Likeother 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 mostimportant neurochemicals produced in the body.
"Using sperm ofnonsmokers, we reported previously that the addition of nicotinechanged three sperm functions required to fertilize an egg.
"Inthis new study, we examined whether sperm from chronic tobacco smokersare defective in binding to the zona, the cover surrounding an egg,"said Burkman. "Our results could mean that heavy smoking overloads thenicotine receptor in human sperm and in the testes, leading to adecline in fertilizing potential."
The study involved 18 men whoreported smoking at least four cigarettes a day, every day, for morethan two years. On average, these men had smoked for about 15 years.Their sperm function was compared to that of non-smoking donors whoserved as controls and whose fertilizing capacity had been confirmed.
Usinga test called the Hemizona Assay developed by Burkman, the researcherscut a zona in half, placing one half with a smoker's sperm and thematching half with control sperm. After two to three hours ofincubation, researchers counted the number of sperm attached tightly tothe outside of each half.
The number of attached sperm from thesmoker was compared to the control number, which gave a ratio or index.The Hemizona Assay has been shown to predict fertilization failureduring in vitro fertilization.
"To fail, the index must be lessthan 65, meaning that the smoker's sperm had less than 65 percent ofthe fertilizing capacity found in the donor," Burkman said. "An indexbelow 36 identifies a severe loss in fertilizing capacity."
Resultsshowed that the sperm from almost two-thirds of the smokers failed thetest, while the remainder showed normal function. Almost all thesmokers whose sperm failed the test had an index of 36 or less, with anaverage of 25.
"None of these men had a zero fertilizingpotential," said Burkman, "but the results mean that their sperm hadonly 25 percent of the fertilizing function found in nonsmoking men.The data also showed that the men who failed were smoking about twiceas many cigarettes per day, an average of 19 per day, compared to thesmokers who passed the assay."
As another way to understand theimpact of smoking, the researchers calculated a "smoking load" for eachsmoker by multiplying the number of cigarettes smoked per day by thenumber of years smoked. The load varied from 16 to 750 for the 18 men.
Resultsshowed that the men who smoked fewer cigarettes for fewer years hadsmaller smoking loads, ranging from 16 to 200. In this group, 71percent passed the Hemizona Assay, indicating normal fertility. Theremaining men had a high smoking load, and only 18 percent passed theassay.
"Specialized testing clearly reveals a significant drop infertility potential for men who are heavy tobacco smokers," saidBurkman. "Smoking men also should be aware that smoking can damagetheir sperm DNA, passing on faulty DNA to their baby. Concerned smokersshould quit or be tested in a local andrology laboratory."
Burkman added that other scientists have shown a similar decline in fertility among women who are heavy smokers.
RoxanneMroz and MaryLou Bodziak, UB research associates, contributed to thiswork, along with UB undergraduate students Stuti Tambar, Brian Telesz,and Scott Beardsley.
The research was funded by the Philip Morris External Research Program.
TheUniversity at Buffalo is a premier research-intensive publicuniversity, the largest and most comprehensive campus in the StateUniversity of New York.
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