(CNN) — Fruits and vegetables are an essential part of a healthy pregnancy diet, providing vitamins and fiber. Yet some might also come with pesticide residues.

Among women undergoing infertility treatment in the United States, consuming more fruits and vegetables with high amounts of pesticide residue was associated with a lower chance of pregnancy and a higher risk of pregnancy loss, according to a study published in the journal JAMA Internal Medicine on Monday.

Pesticides are pest-killing substances often applied to fruits and vegetables to help protect them — and us — against harmful mold, fungi, rodents, weeds and insects. There has been growing concern that exposure to pesticides can be tied to certain acute and chronic human health concerns.

“Most Americans are exposed to pesticides daily by consuming conventionally grown fruits and vegetables,” said Dr. Yu-Han Chiu, a research fellow in the department of nutrition at the Harvard T.H. Chan School of Public Health and first author of the study.

“There have been concerns for some time that exposure to low doses of pesticides through diet, such as those that we observed in this study, may have adverse health effects, especially in susceptible populations such as pregnant women and their fetus, and on children,” she said. “Our study provides evidence that this concern is not unwarranted.”

Yet the findings should be digested with caution, said Janet Collins, executive vice president of science and regulatory affairs for CropLife International, a trade association representing the manufacturers of pesticides. Collins was not involved in the study.

“The JAMA research publication does not show a direct link between pesticide residue intake and pregnancy outcome, as the authors state. This is a hypothesis generating study, and as the authors recommend, we agree that before a definitive outcome can be established the issues require further study,” she said in an emailed statement.

How harmful are pesticide residues?

The study involved 325 women between 18 and 45 who were undergoing infertility treatment with assisted reproductive technology at the Massachusetts General Hospital, the researchers said.

The women completed a diet assessment questionnaire and had their height, weight and overall health measured, while the researchers accounted for confounding factors that could influence the study results, including their intake of supplements and residential history.

The researchers analyzed each woman’s pesticide exposure by determining whether the fruits and vegetables she consumed had high or low levels of pesticide residues, based on reports from the US Department of Agriculture’s Pesticide Data Program, which monitors the presence of pesticides in foods sold throughout the United States.

Some fruits and vegetables with a low amount of pesticide residue include avocados, onions, dried plums or prunes, corn and orange juice. Those with a high amount include fresh plums, peaches, strawberries, spinach and peppers.

The researchers found that, compared with women who ate less than one daily serving of high-pesticide-residue fruits and vegetables, those who ate 2.3 servings or more had 18% lower probability of getting pregnant and 26% lower probability of giving birth to a live baby.

Consuming fruits and vegetables with a high amount of pesticide residue was positively associated with the probability of losing a pregnancy, the researchers found.

However, consuming low-pesticide-residue fruits and vegetables in lieu of high-pesticide-residue foods was associated with higher odds of pregnancy and giving birth, the researchers found.

“Although we did find that intake of high-pesticide-residue fruits and vegetables were associated to lower reproductive success, intake of low-pesticide-residue fruits and vegetables had the opposite association,” Chiu said.

“A reasonable choice based on these findings is to consume low-pesticide-residue fruits and vegetables instead of high-pesticide-residue ones. Another option is to go organic for the fruits and vegetables known to contain high pesticide residues,” she said. “It is very important to keep in mind that, as far as we are aware, this is the first time that this association is reported, so it is extremely important that our findings are replicated in other studies.”

However, purchasing organic fruits and vegetables can be costly, said Irva Hertz-Picciotto, a professor and director of the Environmental Health Sciences Center at the University of California, Davis, who was not involved in the study.

“This is more difficult for those already vulnerable due to their socioeconomic circumstances. Avoiding pesticides becomes an ‘environmental justice’ issue, making it all the more important to reduce use of pesticides throughout agriculture and adopt more sustainable and health-promoting methods for food production,” Hertz-Picciotto said.

She added that the new study was “very well-executed, thoughtful and thorough” and that although replicating the study would be desirable, the findings provide strong evidence that certain pesticides are associated with reproductive concerns.

Wash your fruits and veggies

Dr. Jorge Chavarro, an associate professor at the Harvard T.H. Chan School of Public Health and senior author of the study, said he was surprised with the findings.

“Going into the study, I was positive that we would find absolutely no relation between exposure to pesticide residues in fruits and vegetables and adverse reproductive outcomes,” he said. “While I think we need more studies to confirm or refute our findings, I am now more willing to pay the extra money for organic apples and strawberries than I was when we started this project.”

The study found only associations between pesticide residue and pregnancy outcomes — not a causal relationship.

The study also has some limitations. For instance, the women’s diets were assessed using self-reports, which leaves room for error, and the women were trying to become pregnant through infertility treatments. More research is needed to determine whether similar findings would emerge among women trying to conceive naturally. Also, more research is needed to connect specific pesticides with the infertility treatment outcomes seen in the study.

The Alliance for Food and Farming, a nonprofit organization comprising organic and conventional farmers, notes on its website that fruits and vegetables are an important part of a healthy diet and that “the mere presence of pesticide residues on food does not mean they are harmful.”

In general, the Food and Drug Administration recommends consuming fruits and vegetables for good nutrition but following safe handling tips, including thoroughly washing fresh produce under running water before preparing and eating.

On the other hand, “the observations made in this study send a warning that our current laissez-faire attitude toward the regulation of pesticides is failing us,” wrote Dr. Philip Landrigan, dean for global health and professor at the Icahn School of Medicine at Mount Sinai, in an editorial accompanying the study in JAMA Internal Medicine.

“We can no longer afford to assume that new pesticides are harmless until they are definitively proven to cause injury to human health,” he wrote. “We need to overcome the strident objections of the pesticide manufacturing industry, recognize the hidden costs of deregulation, and strengthen requirements for both premarket testing of new pesticides, as well as postmarketing surveillance of exposed populations — exactly as we do for another class of potent, biologically active molecules — drugs.”

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