Spending hours on a cell phone each day may affect the quality of a man’s sperm, preliminary research suggests.

In a study of 361 men seen at their infertility clinic, researchers at the Cleveland Clinic found an association between the patients’ cell phone use and their sperm quality.

On average, the more hours the men spent on their cell phones each day, the lower their sperm count and the greater their percentage of abnormal sperm.

The findings, published in the journal Fertility and Sterility, add to questions about the potential health effects of cell phones and other wireless devices. Some studies, for example, have linked long-term cell phone use to a higher risk of brain tumors, though many other studies have found no such connection.

The concern is that, over time, the electromagnetic energy emitted from mobile phones could theoretically harm body tissue — by damaging DNA, for example.

However, the new findings do not prove that cell phones somehow damage sperm, according to the researchers.

“Our results show a strong association of cell phone use with decreased semen quality. However, they do not prove a cause-and- effect relationship,” lead researcher Dr. Ashok Agarwal told Reuters Health.

He and his colleagues based their findings on semen samples from 361 men who came to their infertility clinic over one year. All of the men were questioned about their cell phone habits.

In general, the researchers found, sperm count and sperm quality tended to decline as daily cell phone hours increased. Men who said they used their phones for more than four hours each day had the lowest average sperm count and the fewest normal, viable sperm.

“We infer from our results that heavy cell phone use … is associated with a lower semen quality,” Agarwal said. But whether cell phones somehow directly affect men’s fertility is not clear.

Agarwal said he and his colleagues have two studies underway aiming to shed light on the issue. In one, they are exposing semen samples to electromagnetic radiation from cell phones to see what, if any, effects occur.

The second is a follow-up to the current study that is assessing a larger group of men. Agarwal said this study is more rigorously designed and will account for certain other factors like lifestyle habits and occupational exposures that might affect sperm quality.