A new systematic review and meta-analysis of studies examining sperm counts worldwide has found that sperm counts in Western countries have fallen by over 50% in the last four decades, and this trend shows no sign of slowing down.
Researchers examined data from 185 studies including nearly 43,000 men, and concluded that total sperm counts in Western countries (including North America, Europe, Australia, and New Zealand) fell by an average of 1.6% per year between 1973 and 2011, for a total drop of 59.3%. Sperm concentration (number of sperm per milliliter of semen) followed a similar pattern, falling by 1.4% per year and by 52.4% in total during the same period.
No significant trends were found for sperm counts or sperm concentrations in non-Western countries. However, the data from non-Western countries was poor in quality and quantity, and more research is needed to confirm this finding.
The study did not examine causes for the decline, but the study authors speculated that possible causes may include exposure to pesticide residues and other endocrine-disrupting chemicals, cigarette smoking, obesity, stress, and alcohol consumption, all of which have been shown to affect male fertility. For instance, studies have found that women who smoke cigarettes during pregnancy give birth to sons with decreased sperm counts.
Endocrine-disrupting chemicals often have estrogenic effects that may affect the development of the male reproductive system, especially with prenatal exposure. These chemicals are widespread in the environment, and are found in canned foods, foods stored in plastic containers, personal care and cleaning products, non-stick cookware, and cash register receipts, among other sources.
Another possible contributing factor that the authors did not consider is subclinical deficiency of vitamin A and vitamin D, both of which are critical for spermatogenesis. Intakes of these fat soluble vitamins are often too low in Western countries, because the foods that are rich in vitamin A and D tend to also be high in saturated fat and cholesterol. These foods have been widely demonized due to the alleged link between saturated fat and heart disease, so many avoid them. Rich sources of vitamins A and D include liver and other organ meats, cod liver oil, egg yolks, butterfat, fatty fish, and lard from pastured hogs.
However, the latest research indicates that those who eat the most saturated fat do not have a higher risk of heart disease compared to those who eat the least. And it’s now generally recognized that dietary cholesterol has little effect on blood cholesterol levels. The body makes most of its own cholesterol, and when you eat more of it, your body simply makes less. Dietary cholesterol is not correlated with a higher risk of coronary heart disease.