Are synthetic chemicals disrupting human reproduction and development? Some environmentalists have suggested that certain man-made chemicals in the human diet might be causing lower male sperm counts. These chemicals, called endocrine disrupters, mimic or affect hormones involved in reproduction, such as estrogen.

However, naturally occurring substances in the human diet are far more potent endocrine disrupters than the synthetic compounds most closely identified with reproductive health concerns, such as DDT and PCBs.

• More than 43 plants and foods found in the human diet have been shown to have weak estrogenic effects.

• These foods include garlic, pineapple, peanut oil, oats, soybeans, peas, potatoes, corn and wheat.

• The effects of the compounds in these foods are an estimated 40 million times greater than the effects of synthetic chemicals in normal human diets.

• Tests also have found 31 species of plants and 55 chemical compounds that inhibit the production of sperm in animals, but only a handful cottonseed oil is one are found in the human diet.

Effects on reproduction have been observed outside the laboratory when a large part of the diet consists of a food containing unusually high levels of a natural endocrine disrupter. For example, in the 1940s, many Australian sheep became infertile from grazing on a species of clover that produces estrogen-like chemicals.

Most claims about lower human sperm counts are from a now-discredited statistical study. U.S. data collected from 1938 to 1977 show no decline in sperm counts, and there is evidence that counts have actually increased in the last 25 years. Also, U.S. rates of infertility have remained constant for 30 years. Thus the evidence is that neither natural nor synthetic compounds in food are threatening human reproductive health.

Source: Jonathan Tolman, "Nature's Hormone Factory: Endocrine Disrupters in the Natural Environment," March 1996, Competitive Enterprise Institute, 1001 Connecticut Avenue, NW, Suite 1250, Washington, DC 20036, (202) 331-1010.