The quality of sperm from men in North America, Europe and Australia has declined dramatically over the past 40 years with a 52.4 percent drop in sperm concentration, according to a study published Tuesday.

The research – the largest and most comprehensive look at the topic, involving data from 185 studies and 42,000 men around the world between 1973 and 2011 – appears to confirm fears that male reproductive health may be declining. The state of male fertility has been one of the most hotly debated subjects in medical science in recent years. While a number of previous studies found that sperm counts and quality have been declining, some have dismissed or criticized the studies for things like the age of the men included, the size of the study and other aspects of the selection for the study.

Shanna H. Swan, one of the authors of the new study published in the Human Reproduction Update, said she hoped this broad meta-analysis of all the published literature out there would put some of the uncertainty to rest.

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