While countries like Afghanistan, Mali, Niger, Uganda and Zambia are trying desperately to lower their high birth rates (over 45 per 1000 population), Denmark has the opposite problem – how to raise its birth rate above 11 per 1000 population. Denmark is ranked 185th in birth rate out of 221 world countries, and is increasingly concerned about this because Danes are producing fewer babies than it takes to replace themselves. The situation is worrying demographers, who fear that declining population growth will undermine the country's welfare system.
A new study, conducted by researchers at Rigshospitalet Copenhagen University National Hospital and published in the American Journal of Clinical Nutrition, suggests that one of the reasons for the low birth rate may be the shrinking sperm counts in Danish men, and that they may be shrinking because of their diet.
Men who consumed the most saturated fat had the lowest sperm counts
Collecting diet information and sperm samples from 701 Danish men in their early twenties who were receiving military checkups, the researchers found that men who consumed the most saturated fat – commonly found in meats and rich cheeses – had a 41% lower sperm concentration than men who ate less saturated fat. The subjects were further broken down into four groups, depending on their caloric intake, which enabled the researchers to demonstrate that the more saturated fat they ate, the lower their sperm concentration and semen counts fell.
Men who consumed 15% of their calories from saturated fat had a sperm concentration of 45 million per milliliter with a sperm count of 128 million, while those who got only 11% of their calories from saturated fat had a sperm concentration of 50 million per milliliter with a sperm count of 163 million. Eighteen percent of the men who ate the most saturated fat fell short of the World Health Organization's definition of what a normal sperm concentration per milliliter is, while only 13% of the men who ate the least saturated fat did.
This research is far from the first to link diet and decreased sperm production and quality. A 2011 Brazilian study found, for example, that men who ate more whole grains – such as wheat, oats, and barley – had higher sperm concentrations and motility. And a study in France (where diets are also high in meats and rich cheeses) found that sperm concentrations had fallen from an average of 74 million per milliliter in 1989 to about 50 million in 2005.
Correlation is not causation
Lead study author Tina Jensen, MD, PhD cautions, "We cannot say that it has a causal effect, but I think other studies have shown that saturated fat intake has a connection to other problems and now also for sperm count." She says that although the study does not rule out the possibility that other lifestyle factors produce the decreased sperm counts, her findings may help to explain studies that have found falling sperm counts in many countries around the world, many of them with diets newly rich in saturated fats as a result of improving economies and the ready availability of fast foods.
According to Jensen, the next step is to try to find the mechanism by which saturated fat could influence sperm count, and to conduct tests to see whether sperm counts increase when men cut down the amount of saturated fat they consume. Until then, it's too early to tell all men with low sperm counts to cut down on saturated fat. But it's probably not a bad idea, she adds, because of the numerous studies linking saturated fat with other health problems, such as cancer and heart disease.