Pesticide, Smoke & Outcomes
An estimated 15 percent of all couples have trouble conceiving, and although there are known risk factors that can account for the problem, “there’s a lot that can’t be accounted for,” says John Meeker, an assistant professor of environmental health sciences.
Moreover, there’s evidence that male sperm counts are now on the decline, and researchers aren’t sure why.
Meeker, a specialist in exposure assessment, is looking at both secondhand smoke and pesticides to see whether there may be a link between human exposure to these substances and pregnancy outcomes. It’s challenging work, “because you have to make sure you measure the exposure accurately and precisely, or it can lead to misclassification,” he says.
In a study supported by the Flight Attendant Medical Research Institute, Meeker is examining the effects of secondhand smoke on pregnant women. Because this study draws on data gathered from couples who were having difficulty conceiving and thus underwent artificial reproductive technology, Meeker can look at a range of stages between conception, clinical pregnancy, and birth. He’s using blood and urine samples as well as follicular fluid, a potentially new exposure marker, to measure levels of cotinine—a biological marker of tobacco exposure. He’ll then correlate this data with pregnancy-rate and birth-rate and time-to-pregnancy data to see if there’s evidence of a connection.
In a second study, Meeker is looking at pesticide exposure and its potential link to male reproductive health, including intermediate endpoints such as semen quality, DNA damage in sperm cells, and hormone levels. Meeker and his colleagues are measuring chemicals at low concentrations, similar to the levels found among the general population. But he points out that even low levels of exposure to hormonally active chemicals can throw off the body’s balance of hormones that are involved in reproduction.
Already, he has found links between pesticide metabolytes and certain intermediate measures of male reproductive health, and at a subsequent stage of his research, Meeker will account for simultaneous exposure to multiple chemicals. For example, he will factor out fathers and mothers who are exposed to secondhand smoke.
Meeker is especially interested in the moment of implantation, “which is where most pregnancies fail.” Because they often go undetected, such pregnancies are generally not even viewed as pregnancies.
Although at this point Meeker’s pesticide research won’t be able to prove direct causality, as an animal or longitudinal study might, he is still hopeful that his work can provide further information on the connection between pesticides and human reproduction.
His overarching goal is to identify the limitations of exposure biomarkers and then improve on them in epidemiological study designs. Looking ahead, he’d like to examine individual susceptibility and gene/environment interactions as they relate to some of these exposures and outcomes.
Photo by Peter Smith
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