Beginning at age 30, testosterone levels drop, on average, about 1 percent a year. Insurance companies typically require two morning testosterone readings of less than 300 nanograms per deciliter plus symptoms of low testosterone before they reimburse for supplements. (For a 40-year-old, a morning testosterone reading may be 200 points higher than in the evening, versus a 50-point difference for a 70-year-old.) (Testosterone levels declined among those rooting for the losers.) Obesity causes testosterone levels to plummet — while losing 10 percent of body fat can increase levels by 100 points.

Source: New York Times March 27, 2018 18:00 UTC