"Men in this study had not attempted to have children before, so we do not know how their own fertility is influenced by TV watching or physical activity," Chavarro said.
"We know from other studies that sperm counts are related to fertility -- higher sperm counts are related to higher fertility. Men with low sperm counts can still father children although they may have difficulties doing so," he said.
One expert said there are too many factors to consider to say TV is responsible for a lower sperm count. There's an association, but it isn't necessarily the cause, said Dr. Pravin Kumar Rao, an assistant professor of urology and director of reproductive medicine and surgery at Johns Hopkins University.
"The results are believable from a physiological standpoint, but it's difficult to conclude for sure that it's TV that lowers sperm count," he said.
Other factors could account for the finding, such as whether the men who were TV watchers had other undiagnosed medical conditions that might also affect sperm count, like diabetes or high blood pressure, Rao said.
"Exercise and a sedentary life style most likely have an effect on fertility, but I am not sure if we can quantify how much is due to one factor versus another," he said.
However, Rao does have a takeaway message for men.
"I tell my patients the testis prefers to have a very healthy and very stable environment to do its work the best," he said, which means staying active and eating healthfully. "Living a healthy lifestyle can help your sperm production," Rao said.
To learn more about male infertility, visit the U.S. National Library of Medicine.
SOURCES: Jorge Chavarro, M.D., assistant professor, nutrition and epidemiology, department of nutrition, Harvard School of Public Health
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