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Most Americans think nothing of drinking two, three, four, or even five cups of coffee every day. Just in 2015 a US government panel proclaimed that coffee is part of a "healthy lifestyle" and up to five cups a day won't be harmful to health, and may be beneficial. Sure, there are people who need to restrict their coffee consumption due to anxiety disorders, diabetes, or high blood pressure, but tens of millions of Americans, and people in northern Europe and Latin America, regard coffee almost as a health food.
One group, however, probably needs to limit or eliminate coffee consumption. That group is couples, both women and men, who are seeking to have a baby.
Coffee Consumption May Increase the Risk of Miscarriage
A study conducted by the Ohio State University and the National Institutes of Health and published in March 2016 in the medical journal Fertility and Sterility reports a worrisome link between coffee consumption and miscarriage.
Scientists at Ohio State University recruited 501 couples seeking to have children between 2005 and 2009. Both partners were asked to record their daily use of coffee and other caffeinated drinks, cigarettes, alcohol, and multivitamins during pre-conception and early pregnancy. They were asked to use ovulation detection kits and digital pregnancy detectors to confirm that they both became and stayed pregnant. Since miscarriage in the first month of pregnancy can be difficult to detect, even by the mother, conversion of a positive pregnancy test to a negative pregnancy test, onset of ovulation or menstruation, and clinical findings at the doctor's office were all counted as pregnancy losses.
The study found that couples who drank more than two caffeinated beverages per day during the weeks before conception had a higher risk that the mother would miscarry. That finding applied not just to women but also to men in the couples who were trying to conceive.
The study did not just find that the behavior of the male matters, too. With regard to caffeine consumption, the study found that the behavior of the father was equally important as the behavior of the mother in the weeks leading up to conception.
It's relatively well established that caffeine consumption affects sperm quality. A study of 2,554 young men in Denmark, published in 2010 in the American Journal of Epidemiology, reported that those who consumed more that 14 half-liters of soda per week or 800 mg of caffeine per day (equivalent to eight cups of coffee per day, or three or four energy drinks) had reduced sperm concentration and sperm count. In the Ohio State study, about 1/3 of the women who drank more than two cups of coffee per day, or the equivalent, suffered at least one miscarriage.
The study also found that couples who lost babies also tended to be on the older side, 35 or older. It could be that caffeine has a greater effect on aging sperm and aging eggs that somehow leads to miscarriage. Or it could be that caffeine energizes sperm that otherwise would not be strong swimmers and would have never reached the egg. On the plus side, mothers to be who took a daily multivitamin were less likely to experience miscarriage.