Are dietary pesticides associated with infertility in men?

Male infertility accounts for up to 30% of couples seeking help with conception with diet, alcohol consumption and smoking being three of the biggest contributors to the decrease in male fertility. Male infertility usually is described as a decrease in semen quality or quantity. In the 1970’s, there were a number of cases of infertility in workers at a pesticide factory. It was reported that longer exposure to pesticides in these workers was associated with higher levels of hormones that can decrease sperm count. This however, was a case where the workers were likely exposed to amounts of pesticide that the common everyday person would not be. More recently, a couple systematic reviews (1, 2) found that pesticide exposure whether through occupation or through the environment might be linked to decreased sperm quality. Until recently however, there had yet to be a study that looked at how dietary exposure to pesticides may relate to sperm quality and quantity. Now, a study out of the Chan Public School of Health at Harvard suggests that there may be a link between the amount of pesticides you ingest and the amount of sperm a male has.

Before we get into the results I will caution the reader that this is an observational study (case control study). This means they found a group of individuals to observe and then related the measure of something (in this case pesticide exposure) to something else (sperm count). Observational studies are important first steps at letting us know whether two things may be related for future, more in depth studies but they also do not provide the most concrete evidence available. They can be subject to selection bias (picking a group of people more likely to develop the thing you are looking for) and they can also have difficulties with confounders (other exposures that could affect the outcome). I will get into the limitations of this study later. But first, the results which are interesting but should be taken cautiously.

The researchers surveyed 155 men who were taking part in fertility treatment at a medical facility as part of an ongoing study. They asked the men what their diet consisted of and then sperm samples were taken for an 18 month period following this questionnaire. The researchers then calculated the amount of pesticide each man had been exposed to by using available data on the levels of pesticides on commonly eaten fruits and vegetables. Depending on the fruits and veggies eaten by each men, their pesticide exposure can be grouped into one of four groups from low exposure to high exposure. What they saw was that the men who had theoretically been exposed to the most pesticide in their diets had a 49% lower sperm count then the men who had the least pesticide in their diet. They also had 32% more abnormal looking sperm then the men who had the least pesticide exposure. It is important to note that the amount of fruits and veggies each man ate was unrelated to the quality or quantity of the semen in the men. Also, the men who had been exposed to low or moderate levels of pesticide actually had a higher number of normal looking sperm, so that was slightly odd. The researchers also controlled for other factors that may affect sperm count like smoking, weight and age.

Now, things to be cautious about:

  • The first thing to note is that the men in this study were already at the clinic for problems with fertility so this population can be considered biased or not generalizable to the whole population. Since the men had low sperm counts to begin with we cannot know if this was because of the pesticides or some other factor. Need a different population and different study to answer that question. All we can say from this study is that the two may be associated.
  • Since this is a result dependant on a correlation, it could be just as likely that men who already have low sperm counts are more likely to eat more fruits and veggies and therefore have more pesticide exposure. People with infertility problems may begin to try and eat healthier in the hopes that it will help. If this is the case, the low sperm counts would not be caused by the pesticides. In support of this notion, the men with the lowest sperm count had the highest daily energy consumption, although not necessarily all from fruits and veggies.
  • It is also important to note that the sample size here is relatively small (around 39 in each category).
  • The men could have some susceptibility to pesticides or a predetermining factor (genetics) that causes them to have low sperm count to begin with. Again, this population may not be a good representation for the rest of men. A better population would be to compare the men’s sperm count and shape over time as they continue to eat their normal diets. Who’s to say some of the men had lower sperm counts to begin with. If we could know the change in the sperm count over time then we would have better evidence.
  • They never directly measured the amount of pesticide that the men consumed. They relied on recall of diet, something that is subjective and can be prone to error if people feel ashamed of their diet. If the men didn’t give all their dietary information correctly, or didn’t say if the food was organic, the researchers may have over-estimated the amount of pesticide each person was exposed to. This would make the results less significant or not at all. A better study in the future would measure the amount of pesticide each person consumed instead of estimating it. This however, is costly.

Do pesticides affect male fertility? The question is far from answered. We will still need more comprehensive studies on a larger, more relatable population and studies determining the mechanism for this effect. Until then, organic food may offer some relief from pesticides but beware, organic foods are far from free of pesticides (1, 2). If you are worried about pesticides just remember, the amount on both organic and non-organic food falls within acceptable levels and if you spend the time to wash you fruits and veggies you can reduce your exposure to pesticides.

Photo credit: Ian Gallagher Flickr

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