The common, unprescribed painkiller, also known as acetaminophen, has been linked to infertility as it was discovered couples in which the male had high levels of the drug in his urine took longer to conceive.
The National Institutes of Health analysed data from the Longitudinal Investigation of Fertility and the Environment (LIFE) study, which examined links between lifestyle - including exposure to environmental chemicals - and fertility. A total of 501 couples enrolled in the LIFE study from 2005 to 2009, with the women's ages ranging between 18 to 44, while the men were older than 18. Participants gave a single urine sample upon starting the study, which was tested to measure the paracetamol content, and women were found to have a higher average level than men.
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However, there was no reduced chances of becoming pregnant because of this, whereas couples in which the men had high levels - more than 73.5 ng/ml - were less likely to conceive than those who had lower measurements.
Paracetamol is often used to relieve pain and hay fever, and it is also a compound produced when the body breaks down the chemical aniline, used to make rubber, and colouring agents used in food and clothing.
"At this point, our findings need to be corroborated by future research, and there is no cause for alarm," Dr Melissa Smarr, the study's first author, from NIH's Eunice Kennedy Shriver National Institute of Child Health and Human Development, said.
She adds that the high levels in men were unlikely to stem from taking painkillers but rather being exposed to paracetamol or aniline, or both, in the environment.
Findings were published in online journal Human Reproduction.
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