Most of us think nothing of downing a couple of cups of coffee a day. After all, just last year a US government panel declared that coffee could be part of a "healthy lifestyle".
This advice, of course, comes with many caveats. Most people know that those with high blood pressure, diabetes or other health conditions may want to be more conservative in their caffeine intake. But a new study raises questions about a different subgroup: couples seeking to have a baby.
A study conducted by the US National Institutes of Health and Ohio State University and published this month in the journal Fertility and Sterility has found a worrisome link between caffeine consumption and miscarriage.
The analysis involved information from the Longitudinal Investigation of Fertility and the Environment Study, which includes 501 couples interested in having children who were recruited to participate between 2005 to 2009.
The men and women were asked to record their daily use of cigarettes, caffeinated drinks, alcohol and multivitamins during pre-conception and early pregnancy.
They were asked to use ovulation detection and digital pregnancy kits to track the pregnancies. A pregnancy test's conversion from a positive to negative, onset of menstruation or clinical confirmation were all categorized as pregnancy losses.
The data shows that couples who drank more than two caffeinated drinks a day during the weeks before conception had a higher risk that the woman would miscarry. That's right - the study found that both Mum's caffeine intake and Dad's caffeine intake could play a role.
"Our findings also indicate that the male partner matters, too," said Germaine Buck Louis, who directs population health research at NIH's Eunice Kennedy Shriver National Institute of Child Health and Human Development.
In fact, Buck Louis said, a man's pre-conception consumption of caffeinated beverages was just as strongly associated with pregnancy loss as a woman's.
Theories about how a man's caffeine consumption affects a woman's pregnancy mostly involve the sperm. Previous research conflicts on how caffeine affects sperm. But one of the larger studies, published in 2010 in the American Journal of Epidemiology and based on a sample of 2,554 young Danish men, found that high cola intake of more than 14 half-litre bottles a week and/or high caffeine intake of more than 800 milligrams a day were associated with both a reduced sperm concentration and total sperm count. (A typical eight-ounce cup of coffee contains about 100 milligrams of caffeine.)
The NIH study also confirms previous research that shows that women who drink more than two caffeinated beverages each day during early pregnancy - defined in this study as the first seven weeks - may also be more likely to miscarry. In the study, 98 of the 344 women with a singleton pregnancy lost a baby.
The authors of the NIH study cautioned that they don't know for sure whether it's the caffeine that caused the pregnancy loss and noted that those women who drank a lot of caffeine during pre-conception and lost their babies also tended to be on the older side, age 35 or older.
That could mean that the health of the fetus may have been affected by the advanced age of the sperm and egg in older couples or by environmental exposures that could become cumulative over time as people age.
Finally, there was one piece of positive and practical news in the study: Women who took a daily multivitamin before and after conception appeared to greatly reduce miscarriage risk.