Scientists at the University of Buffalo compared sperm from screened sperm donors to sperm from 18 male smokers. In lab tests, the smokers' sperm was less likely to bind tightly to an egg -- a necessary step for fertilization.
The results were presented in Montreal at the American Society of Reproductive Medicine's annual meeting.
"Specialized testing clearly reveals a significant drop in fertility potential for men who are heavy tobacco smokers," says researcher Lani Burkman, PhD, in a news release.
Men who smoke 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," says Burkman.
Burkman is an assistant professor of urology at the University of Buffalo's medical school. He is also an associate professor and head of the andrology section of the university's gynecology and obstetrics department.
Study of Smokers
The smokers in the study all smoked at least four cigarettes a day for two years or more. On average, they had smoked for more than 15 years.
In a lab test, the sperm from each smoker was exposed to half of an egg for two or three hours. The test was also done with the donors' sperm, using the other halves of the same eggs.
To pass the test, at least 65% of a man's sperm had to bind tightly to the egg's outer layer.
The sperm from 12 smokers (two-thirds of the smokers) failed. Their sperm wasn't totally infertile but showed only one-quarter of normal fertilizing capacity, the researchers note.
"Most of the failed cases (nine out of 12) demonstrated a severe loss in fertilizing capacity," write Burkman and colleagues. Sperm from the other smokers showed normal function.
Smokers' Habits Noted
The men's smoking habits and history seemed important to the researchers.
They calculated each smoker's smoking "load" by multiplying the number of daily cigarettes by the number of years as a smoker. The load varied widely, ranging from 16 to 750.
Eleven men had a high load (200 to 750). Only 18% of them passed the test.
In comparison, 71% of the seven smokers with a lower smoking load (16 to 180) passed the test, the study shows.
"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 [test]," says Burkman in the news release.
Smoking and Sperm
"Like other cells in the body, human sperm carry a receptor for nicotine, which means they recognize and respond to nicotine," Burkman explains.
In previous lab tests, the researchers had exposed sperm to nicotine. That "significantly altered" three important sperm functions, write the researchers.
The topic of nicotine's effects on sperm-fertilization function has been "controversial," write Burkman and colleagues.
Their study was funded by the Philip Morris Research Management Group.