A study by the Metropolitan Life Insurance Company that assessed the vital statistics of more than 10,000 baseball players and general mortality rates in the United States concluded that players whose careers began between 1876 and 1900 experienced only 97% expected mortality, those who debuted between 1901 and 1930 had only 64% expected mortality, and those who debuted between 1931 and 1973 experienced only 55% of expected deaths. As early as the 1930s, big league players were exhibiting either a healthy worker effect or the health benefits of the rigorous fitness regimens of professional athletes, or both. However, in this study, vital data on baseball players were limited to those available in the 1974 Baseball Encyclopedia.[1] Other smaller studies have shown similar results for players who debuted between 1911 and 1915[2] and between 1900 and 1939.[3]
One large study examining major league ballplayers with debuts from 1902 and 2004 found that their expected lifespan was almost five years longer than average 20-year-old American males, and that career length was inversely associated with the risk of death, probably because those who play ball longer gained additional income, physical fitness, and training.[4]