But researchers at the Kaiser Permanente Medical Care Program of Northern California in Oakland were surprised to note that women who drink more than one-half cup of caffeinated tea every day may actually increase their odds of conceiving, according to findings published in the American Journal of Public Health (1998;88:270-274).

The study of 210 women who were trying to conceive found that those who drank as little as half a cup of caffeinated tea each day were twice as likely to become pregnant as women who did not drink tea.

Polyphenolic compounds in tea may promote fertility by inhibiting chromosomal abnormalities, thereby decreasing the number of nonviable embryos, suggested the researchers, led by Bette Caan, Dr.P.H.

And hypoxanthine, another chemical in tea, might be the primary component of follicular fluid contributing to maturation and fertilizability of oocytes.

On the other hand, tea drinking may simply be a marker for a healthier lifestyle that would enhance fertility, Dr. Caan noted. Women who drink tea typically eat less fat, exercise and smoke less than do coffee drinkers, she said.

However, "there may still be a [negative] relationship between caffeine and pregnancy, so that women should still be cautious about the amount of caffeinated beverages they consume during pregnancy," said Dr. Caan, a senior investigator at Kaiser Permanente.

All the women reported their caffeine consumption and pregnancy status monthly and were followed for 12 months or until they became pregnant. The positive effects of tea drinking were only observed in the first three cycles.

Other researchers admitted the possibility that drinking tea may help fertility, but the higher pregnancy rate observed in tea drinkers may also possibly be due due to these women having healthier lifestyles.