In my post, The Role of Diet in Declining Sperm Counts, I discussed the association between high saturated fat intake and reduced semen quality and male fertility. One of the most recent articles on the topic found that a significant percentage of the saturated fat intake in the study was derived from dairy products. Residues of industrial chemicals may bioaccumulate up the food chain into cow fat, and some of these lipophilic (fat-loving) chemicals may have hormone-disrupting abilities.
The U.S. Environmental Protection Agency performed a national survey of persistent, bioaccumulative and toxic pollutants in the U.S. milk supply. The EPA team notes that since milk fat is likely to be among the highest dietary sources of exposure to these pollutants, it’s important to analyze the levels. The team tested milk from all over the country and found a witches brew of chemicals. They estimate that dairy products alone contribute about 30 percent to 50 percent of our dioxin exposure. And “like dioxin, other toxic pollutants tend to be widely dispersed in the environment, bioaccumulated through the food chain and ultimately result in low-level contamination in most animal fats.”
This may explain higher pollutant concentrations in fish eaters. Xenoestrogens like polychlorinated biphenyls (PCBs) are associated with the fats of fish or animal flesh and cannot be fully removed by washing and cooking, and so can accumulate in our fat, too. Xenoestrogens are chemicals with demasculinizing or feminizing effects. But even in a non-polluted world, animal foods also have actual estrogen, which are unavoidable constituents (in non-vegetarian nutrition). All foodstuff of animal origin contains estradiol, which is at least 10,000-fold more potent than most xenoestrogens. Dietary exposure—meat, dairy products and eggs—to these natural sex steroids is therefore highly relevant, as the hormones in these animals are identical to our own.
Estrogens are present in meat and eggs, but the major sources are milk and dairy products. By drinking a glass of milk, a child’s intake of estradiol is 4,000 times the intake of xenoestrogens, in terms of hormone activity. Modern genetically-improved dairy cows can lactate throughout their pregnancy; the problem is that during pregnancy estrogen levels can jump as much as 30-fold.
Cheese intake has specifically been associated with lower sperm concentration, and dairy food intake in general has also been associated with abnormal sperm shape and movement. Lower sperm concentrations by themselves may just represent a potential suppression of sperm production due to higher estrogen levels, but abnormal shape and movement suggests that dairy intake may be implicated in actual direct testicular damage.
While milk products supply most of our ingested female sex steroids, eggs are a considerable source as well, contributing about as much as meat and fish. This could be expected, as eggs are produced directly in the hens’ ovaries.
Meat may also come hormone-enriched. In the U.S., anabolic sex steroids may be administered to animals for growth promotion, a practice banned in Europe 25 years ago. A study in New York found progressively lower sperm counts associated with processed meat consumption. However, similar studies in Europe after the ban found the same thing, so it may not be the implanted hormones, but rather a consequence of other things in meat, such as the saturated fat, perhaps by elevating cholesterol.
We’ve known for decades that men with high cholesterol levels show abnormalities in their spermiograms: decreased sperm concentration, about a third of the normal sperm movement, half the normal sperm shape and lowered male fertility. Twenty-five years later, we’re finding the same thing. In the largest study to date, higher blood cholesterol levels were associated with a significantly lower percentage of normal sperm. Cholesterol was also associated with reductions in semen volume and live sperm count and male fertility. These results highlight the role of fats in the blood in male fertility, and should be of concern given the rising prevalence of obesity and cholesterol problems. And although a healthier diet may be associated with healthier sperm counts, cholesterol-lowering statin drugs do not seem to help.
Michael Greger, M.D.