Tea: Can you conceive of this?
The most widely consumed hot beverage in the world, tea can soothe your nerves, purge excess water from the body, and perhaps even fight certain cancers. New data suggest it may also facilitate getting pregnant.
The latter observation emerges from a just-published study of 187 would-be moms by nutritional epidemiologist Bette Caan and her coworkers at the Kaiser Permanente Medical Care Program of Northern California. In the February American Journal of Public Health, they report finding that during the first 3 months that women tried to conceive, those who drank more than half a cup of tea per day proved seven times as likely to succeed as were those who eschewed the brew.
Caan’s team had been interested in probing caffeine’s possible influence on fertility. At least six studies had suggested that a heavy coffee habit or penchant for drinking caffeinated beverages such as cola can lengthen the average time to conception. Three other studies, however, detected no such caffeine-associated delay. And even among the studies that had reported an apparent caffeine lag, some seemed to require an additional cofactor, such as smoking.
These studies all relied on a woman’s ability to recall dietary data from an earlier period. Since memories can prove unreliable, Caan’s team opted instead to survey current beverage habits and then follow the women for a year unless they became pregnant first.
No strong caffeine effect
Over the course of the study, 48 women dropped out for various reasons— usually because they changed their minds about wanting to become pregnant. Of the 139 who remained, 118 eventually conceived.
Ninety-two percent of the surveyed women drank caffeinated beverages. As a group, they averaged a weekly intake of 610 milligrams of caffeine—the equivalent of 6 cups of regular coffee. While the other studies, taken together, had hinted that consumption at or above this level lengthened the time a woman took to become pregnant, the new data do not indict caffeine.
When coffee and colas were analyzed separately, no significant association popped up. "The surprise," Caan says, "was that with the caffeinated tea, there was an increase in fertility—and that most of it was seen in the earliest months of trying." This suggests, she says, "that the effect may only show up in the most fertile of those women who drink tea."
So unexpected were the findings, she says, "that I would not have reported the findings" except that a similar effect had been seen in a Danish study investigating caffeine’s possible link to fertility. In that earlier study, women who drank five or more cups of tea a day appeared to triple their likelihood of becoming pregnant during the study period. "We were unable to test the effects of tea at that level," Caan’s group notes, "since very few of the women in our study had such high consumption levels."
What’s different about tea or tea drinkers?
Some studies have observed that tea drinkers tend to be more likely than coffee drinkers to live a "healthy" lifestyle. However, in the new California study, tea drinkers proved no more likely to exercise, to take vitamin supplements, or to avoid stress than their java-downing counterparts. In fact, women who drank the most tea in the Kaiser Permanente study also ate the most calories and derived significantly more of their calories from fat.
Though tea contains some caffeine, it usually comes to far less than an equivalent-size cup of coffee. However, the shortened lag to conception associated with tea drinking was observed only in women who drank caffeinated tea—not decaf varieties, which in these women tended largely to be herbal brews. Any role of tea in enhancing fertility would appear to trace to something other than caffeine content, Caan’s group concludes.
And certainly, Caan observes, "there are things in tea other than caffeine that might promote fertility," such as the flavonoids and other polyphenolic compounds—usually plant pigments. Several studies have shown that such compounds possess the ability to inhibit chromosomal aberrations, she notes. "And a lot of spontaneous abortions are nonviable embryos with DNA abnormalities."
Moreover, she and her coworkers refer to one study that suggests hypoxanthine—a chemical in most teas—may be a principal component of a natural bodily fluid "that contributes to the maturation and, thus, the fertilizability of [human eggs]."
So green, English breakfast, or Darjeeling, the choice is up to you. Just remember that sipping any of these teas regularly may shorten the time you have to brush up on your lullabies.
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Caan, B, C.P. Quesenberry, Jr., Coates, A.O. 1998. Differences in fertility associated with caffeinated beverage consumption. American Journal of Public Health 88(February):270.
Florack, E., G. Zielhuis, and R. Rolland. 1994. Cigarette smoking, alcohol consumption and caffeine intake and fecundability. Preventive Medicine 23:175.
Raloff, J. 1997. Coffee’s subtle developmental risks. Science News Online (Feb. 22).
Stanton, C.K., and R.H. Gray. 1995. Effects of caffeine consumption on delayed conception. American Journal of Epidemiology 142:1322.
1994. Caffeine linked to miscarriage. Science News 145(Jan. 22):61.
1994. . . . and to reduced fertility. Science News 145(Jan. 22):61.
Kaiser Permanente Medical Care Program of Northern California
Division of Research
Oakland, CA 94611
This week's Food for Thought has been prepared by Janet Raloff, senior editor of Science News.