Decrease in serum leptin after prolonged physical activity in men

Purpose: This study was designed to determine whether serum leptin levels were affected by a 5-d military course after 3 wk of combat training. Methods: 26 male soldiers (mean age = 21 +/- 2 yr) were examined at the beginning of the training program and just at the end of the 5-d course. The combination of continuous heavy physical activity and sleep deprivation led to energy deficiency. Blood samples were analyzed for serum leptin, insulin, cortisol. adrenocorticotropin (ACTH), and testosterone; plasma was analyzed for free fatty acids (FFA), glycerol, glucose, and catecholamines. Results: At the end of the 5-d course, there was a significant reduction in serum leptin (0.40 +/- 0.04 ng(.)mL(-1) versus 1.47 +/- 0.14 ng(.)mL(-1), P < 0.001), i.e., a mean decrease of 67.00 +/- 3.75%. Plasma norepinephrine and dopamine rose significantly from 296 +/- 17 ng(.)L(-1) to 672 +/- 48 ng(.)L(-1) and 23 +/- 3 ng(.)L(-1) to 40 +/- 5 ng(.)L(-1) (P < 0.001 and P < 0.01, respectively), whereas epinephrine remained unchanged. Serum concentrations of the anabolic hormone, insulin, fell from 31.17 +/- 3.03 muU(.)ml(-1) to 17.79 +/- 1.58 muU(.)mL(-1) (P < 0.001), whereas plasma FFA and glycerol were increased (P < 0.001, P < 0.05, respectively). A statistically significant correlation appeared between the changes in leptin and insulin (r = 0.5306, P < 0.01). Serum testosterone decreased significantly (P < 0.001), whereas serum cortisol, ACTH, and plasma glucose were unchanged at the end of the course. The training program had no significant effect on mean body mass index. Conclusion: A 4-wk strenuous military training program, which induced an energy deficiency, reduced serum leptin to a third of normal levels. The decrease in serum leptin was attributed to the exercise-induced elevation in catecholamines and hypoinsulinemia.