Milk and Infertility

Women who would like but have failed to conceive a child may want to review how big a role dairy products play in their diet, a new study suggest. A team of researchers in the United States and Finland now reports that where per capita milk consumption is highest, women tend to experience the sharpest age-related falloff in fertility.

With the exception of certain northern European populations and their descendants, most adults lose the ability to easily digest lactose, a sugar in milk. Because lactose intolerance discourages high consumption of milk and other dairy goods rich in galactose -- a sugar apparently toxic to human eggs -- this trait may be beneficial, observe gynecologist Daniel W. Cramer of Harvard Medical School and his coworkers.

Five years ago, Cramer linked galactose consumption with increased risk of ovarian cancer. To look for hints that this sugar might also affect fecundity, his team compared published data from 36 countries on on rates of fertility, per capita milk consumption, and hypolactasia -- the adult inability to digest lactose. In the Feb. 1 American Journal of Epidemiology, they now report a correlation between high rates of milk consumption and waning fertility, beginning in women just 20 to 24 years old.

The strength of that association -- and the rate of fertility decline -- grew with each successively older age group studied. In Thailand, for instance -- where 98 percent of adults are hypolactasic -- average fertility in women 35 to 39 is only 26% lower than peak rates [at age 25 to 29]. By contrast, in Australia and the United Kingdom, where hypolactasia affects only about 5% of adults, average fertility by 35 to 39 is fully 82% below peak rates.

Many factors -- including marriage customs, divorce rates, contraception use, and individual wealth -- affect fertility, the authors concede. However, notes Cramer, the new analysis does offer "demographic confirmation of what we have observed both experimentally, when you feed a mouse high galactose, and clinically, in women with galactosemia [an inability to metabolize galactose]." Women with this disorder who have high concentrations of the sugar in tissue are infertile, he observes.

From SCIENCE NEWS, 3/12/94.