This podcast episode talks about new research showing that men’s hormone levels—specifically testosterone and luteinizing hormone (LH)—have dropped a lot over the past 50 years. The study looked at data from over a million healthy men and found that this drop isn’t just because men are older or heavier today.

Previous studies already showed that sperm quality is getting worse, but this new research suggests that the problem starts higher up, in the brain areas that control hormone production. Scientists aren’t sure exactly why this is happening. They looked at things like environmental changes and shifts in the population but couldn’t find a clear explanation, so it’s probably caused by many things working together. In summary, healthy men today have much lower key hormone levels than men did decades ago, and researchers are still trying to figure out why.