A new study reports significant declines in sperm count among men from Western countries — and scientists aren't sure why.
The researchers found in the past few decades, total sperm count in men from North America, Europe, Australia and New Zealand declined by almost 60 percent, while sperm concentration dropped 52 percent.
Declines in sperm count have been reported since 1992, but previous studies were criticized for small sample numbers and conflicting results. This new study takes a broader approach, looking at more than 7,000 studies from 1973 to 2011.
"These findings have wide implications for public health," said Dr. Hagai Levine, head of the environmental health track at the Hebrew University of Jerusalem. "Sperm count is the best measure of male fertility. Furthermore, recent evidence shows that low sperm count also predicts morbidity and mortality."
But it's unclear what's driving the decline. Mayo Clinic says infections or hormone imbalances can affect sperm count but says environment and lifestyle can, too. This includes anything from chemical exposure to drug use and obesity.