Abstract

Main results and the role of chance: Men had a median (interquartile range) age of 36 (33, 39) years and were predominantly Caucasian (87%). Of the men who completed the survey, 12% reported often lifting or moving heavy objects at work, 6% reported heavy physical exertion at work, and 9% reported evening or rotating shifts. Men who reported often lifting or moving heavy objects at work had 46% higher sperm concentrations (P = 0.01) and 44% higher total counts (P = 0.01) compared with men who reported never lifting or moving heavy objects at work. Similar results were found for men working in rotating shifts compared to those in day shifts, as well as for men involved in heavy levels of physical exertion compared to those with light levels at work. We also found that men involved in heavy/moderate levels of physical exertion at work had higher circulating testosterone concentrations compared to those with lighter exertion (adjusted means of 515 and 427 ng/dl, respectively, P = 0.08), and men who often moved/lifted heavy objects at work had higher estradiol concentrations, compared to those who never did (adjusted means of 36.8 and 27.1 pg/ml, respectively, P = 0.07). Men working evening/rotating shifts had 24% higher testosterone (P = 0.04) and 45% higher estradiol concentrations (P = 0.01), compared to men working day shifts. No associations were observed for ejaculated volume, total motility, morphologically normal sperm, or serum FSH and LH concentrations.