Milk may impair infertility in women ... as lead can in men.
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 in Boston and his coworkers.
Five years ago, Cramer linked galactose consumption with increased risk of ovarian cancer (SN: 7/22/89, p. 52). To look for hints that this sugar might also affect fecundity, his team compared published data from 36 countries on rates of fertility, per capita milk consumption, and hypolactasia - that 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 t o 39 is only 26 percent lower than peak rates (at age 25 to 29). By contrast, in Australia and the United Kingdom, where hypolactasia affects only about 5 percent of adults, average fertility by 35 to 39 is fully 82 percent 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.
... as lead can in men
Though several studies have demonstrated that high exposures to lead can impair male reproduction, no one has understood precisely how the heavy metal wreaks its havoc. Now, researchers at the University of California, Los Angeles, School of Medicine report that the toxic metal may alter sperm function by suppressing circulating concentrations of the male sex hormone testosterone.
Rebecca Z. Sokol and her coworkers treated mature male rats to regular water or drinking water laced with lead. Rodents exposed to lead received enough to alter serum testosterone concentrations without affecting their apparent health. After 2 to 9 weeks, sperm from each rat were incubated with eggs from females raised on a lead free diet.
The researchers found no structural abnormalities in sperm from the lead-treated animals. However, these sperm proved about 30 percent less successful at penetrating eggs than did sperm from untreated rats. Even after penetrating an egg, lead-exposed sperm had a more difficult time fostering those initial stages of development in which one cell begins dividing into many,
In the February TOXICOLOGY AND APPLIED PHARMACOLOGY, SSokol's team concludes that by disrupting testosterone's stimulation of the testes, lead appears to trigger a cascade of events that "not only impairs sperm penetrating ability, but also diminishes the ability of lead-exposed sperm to physiologically fertilize the eggs that they have penetrated."
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|Date:||Mar 12, 1994|
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