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Dec. 20, 2000 -- A new report from Sweden has some bad news for pregnant women who love their coffee, tea, and/or chocolate. The study -- appearing in the Dec. 21, 2000 issue of The New England Journal of Medicine -- finds that overindulging in caffeine can double the risk of early miscarriage.
If anything, the study is more proof of the old adage that too much of any one thing is probably not good for you, says Mark A. Klebanoff, MD, director of the National Institute for Child Health and Development's Division of Epidemiology, Statistics and Prevention Research.
"I think the message is, if you are a heavy coffee drinker, moderation is the best advice," says Klebanoff, who was not involved in the study. But, he says, despite this and several other studies suggesting harm from caffeine, there still isn't enough hard evidence to convince most experts that it somehow causes miscarriages.
The researchers compared over 560 women who had miscarriages between six and 12 weeks of pregnancy with a comparison group of women with ongoing pregnancies.
Only nonsmoking women had an increased risk of miscarriage linked to caffeine intake. At a rate of 500 mg of caffeine per day -- about five cups of regular brewed coffee -- the rate of miscarriage doubled among this group. Still, an increased risk of miscarriage was found even at levels of 100 mg. The researchers say that they believe the study demonstrates that caffeine may be most harmful during the first trimester rather than later on in pregnancy.
The risk of miscarriage in smokers was not increased by caffeine use; a finding the authors say may be explained by the fact that smoking speeds up the rate at which caffeine gets eliminated from the body.
Studies have suggested that the average American consumes approximately 200 mg of caffeine per day, which is equivalent to about two cups of regular brewed coffee.
All women who miscarried had a higher caffeine intake on average than women who continued their pregnancies, according to lead author Sven Cnattingius, MD, of the Karolinska Institute in Stockholm. But women in the latter group had more nausea, which may have accounted for why they drank less coffee.
What is it about caffeine that could possibly cause miscarriage? The experts don't know. In any case, Klebanoff says it's too premature for doctors to know what exactly to tell women regarding how much caffeine is too much when you're pregnant or trying to get pregnant.
"I can't say there is a safe or a dangerous level at this point. Moderation is just generally the best advice we can give," he says.