Why Have Sperm Counts Dropped?

1 min

An international team of researchers has found that sperm counts among men in developed countries declined by nearly 60 percent from 1973 to 2011 and that the downward spiral is continuing. The investigators – from Israel, the U.S., Brazil, Denmark and Spain – analyzed 185 studies that included data on 42,935 men from 50 countries who provided semen samples. They also found that during the study period, sperm concentration dropped by 1.4 percent per year, adding up to a 52 percent decline over nearly 40 years. No such declines were seen among men living in South America, Asia and Africa. (Sperm count is the number of sperm in a semen sample, while sperm concentration is the number of sperm per milliliter of semen.)

The monthly probability of conception declines when sperm concentration drops below 40 million per milliliter. A high proportion of the men in the study had sperm concentrations below this level. The researchers also noted that low sperm counts are associated with “overall morbidity and mortality.” Earlier studies have linked low sperm counts and other sperm abnormalities to cancer, cardiovascular disease and early death. However, experts commenting on the new report pointed out that longevity has been increasing in the countries where sperm counts have been dropping.

The study didn’t delve into the causes of the declines, but a number of possibilities have been suggested, including exposure to pesticides and other chemicals, smoking, stress, obesity and even climate change. Some of these influences might begin in the womb. For example, research has shown that when women smoke during pregnancy, their sons will have lower sperm counts whether or not they themselves eventually smoke.

Other studies have found that exposure in the womb to endocrine-disrupting chemicals such as the phthalates in some plastics can affect the development of the male reproductive system and fertility. Some experts suggest that obesity and stress can have an impact as well. Coincidentally, results of another study published in July (2017) showed that up to 90 percent of adult men in developed countries are “overfat,” especially in the U.S. and New Zealand. The term “overfat” refers to excess body fat that can impair health. Even normal weight individuals can have excess body fat, and its consequences could extend to sperm counts and fertility.

Andrew Weil, M.D.

Source:

Hagai Levine et al, “Temporal trends in sperm count: a systematic review and meta-regression analysis.” Human Reproduction Update, July 25, 2017, doi.org/10.1093/humupd/dmx022