According to the Environmental Working Group, a nonprofit advocacy organization, these fruits and vegetables contain the highest levels of pesticides. The organization did not participate in a new Harvard University study of pesticides and male reproductive function. (EWG)

Consumption of fruits and vegetables that contain relatively large amounts of pesticide residue may affect men's sperm counts and the number of normal-looking sperm they produce, a potential factor in fertility problems, Harvard University researchers reported Monday.

The study by researchers at the T.H. Chan School of Public Health, described as the first to link pesticides in fruits and vegetables to reproductive problems, leaves many questions unanswered. Because of the study's design, the researchers could not determine whether the pesticide residue caused the problems they found in the sperm of 155 men who provided samples at a fertility clinic.

But the results were clear enough to "suggest that exposure to pesticides used in agricultural production through diet may be sufficient to affect spermatogenesis in humans," the researchers wrote in their paper, published online in the journal Human Reproduction.

Pesticides have long been suspected for a possible impact on sperm production among men who work with them or are heavily exposed to them in the environment. And while consumption of pesticide residue does increase the chemicals' presence in urine, there is so far little evidence that affects human health, according to Jorge Chavarro, an assistant professor of nutrition and epidemiology at the public health school, and one of the authors of the study.

The researchers used U.S. Department of Agriculture data to classify the levels of pesticide residue in 35 fruits and vegetables between 2006 and 2012. They asked 155 men how much of each they ate (they averaged .9 daily servings of high-pesticide produce and 2.3 servings of low- to moderate-pesticide fruits and vegetables), then checked their semen samples for a variety of problems.

When they ruled out smoking, obesity, age, physical activity and other factors, they found that men who consumed the largest amounts of high-residue fruits and vegetables had 49 percent lower sperm counts, 32 percent fewer normal-appearing sperm and a 29 percent lower ejaculate volume than men who ate the smallest amounts of those fruits and vegetables.

"I think this raises a lot more questions," Chavarro said in an interview. "It was actually very surprising to me ... that we were able to identify such a strong association, which to me says there is something going on there." But much more research, including a controlled, randomized study, is needed, he said. The study cautioned that because the research subjects were men who already were seeking help with possible fertility problems, the findings may not be applicable to the general public.

[Popular weed killer deemed probable carcinogen by U.N.]

If there is a link, the study also doesn't tell us whether a single chemical in pesticides or many chemicals may be the culprit, Chavarro said. "One of the limitations of this study is that we cannot link exposure to any one pesticide. It may be linking back to a pesticide mixture, which is more difficult to assess," he said.

Nor would washing the foods carefully help eliminate the chemicals, he said. Pesticide residue can get into the roots of fruits and vegetables from the ground and into the substance of the foods themselves, Chavarro said.

Of course, that doesn't mean that people — even men being evaluated for possible fertility problems — should stop eating fruits and vegetables, which are widely recommended as part of a healthful diet. Chavarro said people should choose organic fruits and vegetables, which have been shown to contain much less pesticide residue, if they can, or select fruits and vegetables that don't absorb as much pesticide (see list below).

I've contacted Croplife America, which represents pesticide manufacturers, distributors and users, and am waiting for their reaction to the study.

According to the Environmental Working Group, these fruits and vegetables are least likely to contain pesticide residues. (EWG)