The number of sperm produced by men in some regions of the world has fallen by half over the last 40 years. Between 1973 and 2011, the sperm count in men living in North America, Europe, Australia, and New Zealand decreased by an average of 1.4% per year. There was no decline in South America, Africa, or Asia. The findings raise concerns about male reproductivity. Led by epidemiologist Hagai Levine, of the Hebrew University of Jerusalem in Israel, researchers conducted a meta-analysis of 185 studies published over the past three decades, involving 43,000 men from 50 countries (Human Reproduction Update, July 25). Where there was a reduction in sperm concentration, it fell from an average of 99 million per milliliter (ml) in 1973 to 47 million per ml in 2011—a fall of 52.4%. Although the cause of this reduction is unknown, the authors suggest that low counts could be associated with an unhealthy lifestyle and exposure to chemicals.