Look out, men - smoking and drinking alcohol may affect the quality of your semen.

A group of investigators from Argentina found that men who both drank alcohol and smoked cigarettes were more likely to have a smaller amount of semen, a lower concentration of sperm, and a lower percentage of active sperm than abstainers.

However, these semen alterations were present only in men who both smoked and drank, and not in men with one habit but not the other.

For a normally fertile man, the reductions in semen quality are not enough to render him infertile, study author Dr. Marta Fiol de Cuneo told Reuters Health. However, in men who already have fertility problems, these sperm changes might make the situation worse, she said.

“In conjunction with another deleterious factors they would diminish male fertility,” said the researcher, who is based at the Universidad Nacional de Cordoba.

Cuneo explained that smoking and drinking together may exert “additive” or “synergistic” effects. In the case of synergy, this would mean that one factor enhances the effects of the other, she explained.

In the journal Fertility and Sterility, she and her colleagues write that previous research has investigated the effects of either smoking or drinking on semen quality, with mixed results. However, many of those studies looked at only a small group of men, involved men who may have infertility problems, or could not separate the effects of smoking from drinking, since those habits often go hand in hand, they note.

To investigate the question further, Cuneo and her colleagues asked almost 4,000 men between the ages of 29 and 36 about their smoking and drinking habits, and tested their semen.

The researchers found that men who both smoked and drank showed changes in semen quality, which were not seen in men who had neither or either of these habits.

Men who drank less than 500 milliliters of wine per day - roughly equivalent to 3 glasses - had the same risk of semen changes as men who drank more, and men who limited their cigarettes to less than 20 per day showed similar risks to heavier smokers.

“Men who wish to procreate should be specifically warned of this matter,” Cuneo and her colleagues write.

SOURCE: Fertility and Sterility, August 2004.