Nonsmoking women who drink more than three cups of coffee a day may be less likely to become pregnant than others, according to a Johns Hopkins study.
Consuming more than 300 milligrams of caffeine a day - roughly equal to three cups of coffee - reduces monthly chances of conception by 26 percent, according to the study, published in the latest issue of the American Journal of Epidemiology.Less than 300 milligrams of caffeine a day did not delay conception, it said. One cup of coffee contains about 100 milligrams of caffeine, with 50 milligrams in a cup of tea and 40 milligrams in a can of soda.
"Although a relatively small percentage of reproductive-age women drink more than 300 milligrams of caffeine a day, women who consume caffeine and are thinking of becoming pregnant should be aware of the potential for delayed conception," said researcher Cynthia Stanton.
The retrospective study by Stanton and Dr. Ronald Gray used data from interviews with 1,430 women, conducted from July 1989 through June 1990, regarding more than 2,000 pregnancies.
For decades, questions have been raised about the physical effects of caffeine, particularly on pregnant women. In the 1980s, the U.S. Food and Drug Administration warned pregnant women to reduce or eliminate caffeine use.
However, a study of 2,800 North American mothers published in the British journal Lancet in 1990 showed no relation between caffeine consumption and waiting time to conception.
In the Johns Hopkins School of Public Health study by Gray and Stanton, daily caffeine intake prior to pregnancy was estimated based on a woman's reported consumption during her first month of pregnancy.
The results indicate women consuming 300 milligrams of caffeine were 2.6 times more likely than other women to take at least one year to get pregnant.
The study showed that caffeine had little or no effect on the fertility of women who smoked.