Men who consume the pesticide residue found in many fruits and vegetables may have nearly 50 percent lower sperm count, according to a paper published in the journal Human Reproduction. The study, conducted by a team of Harvard researchers, is the first to examine the link between pesticide consumption and reproductive health.

Researchers collected 338 semen samples from 155 men, between 2007 and 2012, and compared each participants’ fertility data with their self-reported diets. After adjusting for smoking and obesity (two factors known to damage semen), the scientists discovered that men who routinely ate high-pesticide fruits and vegetables—apples, strawberries and peppers—had 49 percent lower sperm counts than men who ate fewer than 1.5 daily servings of those foods. Pesticides also appeared to have a negative effect on ejaculate volume and the percentage of normal sperm in each sample.

Prior studies have tracked lower sperm counts in even larger groups of men, and tentatively linked pesticide exposure to reproductive problems in farmers. But, until now, “it has been incredibly difficult to link pesticide residues in food to any health effects,” says Jorge Chavarro, professor of nutrition and epidemiology at Harvard, and coauthor on the study.

Chavarro cautions that the results do not suggest men should stop eating fruits and vegetables.

“In fact, men consuming the highest amounts of fruits and vegetables known to have lower levels of pesticide residues have higher levels of normal sperm,” he says.

There are several limitations to this study. Pesticide levels were based on self-reports, which are notoriously unreliable, especially over long periods of time. And CASA, the technology used to analyze the semen samples, may be less effective than manual sperm analysis in laboratory research. In any case, the authors stress that this is only an observational study—follow-up studies will be necessary to confirm the effects of pesticides on reproductive health.