Friday November 30 1:33 PM ET
NEW YORK (Reuters Health) - Contrary to what researchers expected to find, women who rapidly metabolize caffeine may be at risk for having a miscarriage, unlike women who take longer to clear caffeine from their bodies.
The new study findings add to the body of research on caffeine and its effects on the risk of early miscarriage.
``There is a longstanding debate about whether caffeine intake during pregnancy can influence a woman's risk for miscarriage,'' according to the study's lead author, Dr. Lisa B. Signorello, an epidemiologist at both the International Epidemiology Institute in Rockville, Maryland, and Vanderbilt University in Nashville, Tennessee.
This debate, she told Reuters Health, ``is not at all resolved.'' Some studies have shown a possible risk associated with caffeine, but others have not, she said.
For purposes of the current analysis, which appears in the latest issue of the journal Obstetrics & Gynecology, the researchers assumed that caffeine increases the risk of miscarriage during the first trimester, although Signorello stressed that this may or may not be true.
``In our study, we wanted to see whether the speed of a woman's caffeine metabolism made a difference in miscarriage risk,'' Signorello said. She noted that genetic differences as well as smoking, eating certain foods and taking some medications may affect how quickly a woman metabolizes caffeine.
The researchers hypothesized that if two women drank the same amount of coffee, the woman whose body broke down caffeine at a slower rate--and thus would have the stimulant in her system longer--would have a greater risk of miscarriage than a woman whose body cleared caffeine more rapidly.
The study included 101 women who had a miscarriage during the first trimester for unknown reasons and a ``control'' group of 953 pregnant women in the first trimester of pregnancy. Signorello's team estimated the speed of caffeine metabolism by measuring factors in urine and blood. They then tried to relate this information, along with how much caffeine the women consumed, to their risk of miscarriage.
The results of the analysis were ``far from conclusive,'' according to Signorello. The investigators found that caffeine intake was a risk factor for miscarriage only for those women who broke down caffeine faster, not slower, than other women.
``Contrary to our original hypothesis, we found that women who are fast metabolizers of caffeine may be at preferentially increased risk of first-trimester miscarriage,'' she said.
She stressed, however, that the findings need to be confirmed in future studies with larger numbers of women. ''These results could have come about through many reasons other than a cause-effect relationship,'' she said.
Both US Pharmacopeia, a non-governmental organization that sets standards for drug manufacturing and dosage, and the Food Standards Agency (FSA) in the UK advise pregnant women to limit their caffeine consumption to no more than 300 milligrams (mg) per day. In the study, the risk was highest for those fast metabolizers who consumed 300 mg or more of caffeine per day.
On average, there are 35 mg of caffeine in a 12-ounce cola, 115 mg in 5 ounces of regular-brew coffee and 40 mg in 5 ounces of regular American tea.
The study was funded in part by the National Soft Drink Association.
SOURCE: Obstetrics & Gynecology 2001;98:1059-1066.