Smoking and excessive drinking are unlikely to harm a man’s sperm, a new study suggests. The study included more than 2,200 men seen at fertility clinics in the United Kingdom, who answered lifestyle questionnaires. The researchers then analyzed the men’s level of sperm, HealthDay reports.

Men’s use of tobacco, alcohol and recreational drugs had little effect on their levels of swimming sperm, the researchers found.

Some lifestyle factors did appear to affect sperm levels. Men with low levels of swimming sperm were 2.5 times more likely to have had testicular surgery, twice as likely to be black, and 30 percent more likely to not wear boxer shorts, to work in a job involving manual labor, or not to have had a child.

“Despite lifestyle choices being important for other aspects of our health, our results suggest that many lifestyle choices probably have little influence on how many swimming sperm [men] ejaculate,” researcher Dr. Andrew Povey of the University of Manchester’s School of Community Based Medicine, said in a university news release.

U.S. researchers told HealthDay they were not convinced by the findings, which are published in Human Reproduction.

“I am concerned that this limited and isolated study will convey the wrong message to couples desiring to become parents,” said Dr. Natan Bar-Chama, Director of the Center of Male Reproductive Health at Mt. Sinai Hospital in New York City. He said that a number of previous studies indicate that illicit drug use such as marijuana, as well as chronic cigarette smoking, impairs semen and fertility.

Dr. Avner Hershlag, Chief of The Center for Human Reproduction at North Shore University Hospital in Manhasset, New York, noted, “The study did not find that cigarette smoking was a culprit, yet did not examine the effect of passive smoking on the female partner’s fertility.”