Successful physical exercise-induced weight loss is modulated by habitual sleep duration in the elderly: results of a pilot study.

Although it is widely accepted that physical exercise promotes weight loss, physical exercise alone had been found to result in only marginal weight loss compared to no treatment. Interestingly, both subjective and objective sleep duration have been shown to be negatively correlated to the body mass index (BMI). Despite this growing evidence of a relation between sleep duration and body weight, the role of habitual sleep duration in physical exercise-induced weight loss has not been studied so far. Twenty-two healthy elderly good sleepers aged 61-76 years (mean 68.36 years, 55 % female, BMI mean 25.15 kg/m) either took part in a 12-week aerobic endurance training (3 × 30 min/week) or in a relaxation control (2 × 45 min/week). The BMI was assessed prior to and after intervention. Subjects maintained sleep logs every morning/evening during the training period, allowing for calculation of habitual sleep duration. Besides a significant main effect of the type of training, a significant interaction of type of training and habitual sleep duration was observed: while after treadmill training subjects who slept less than 7.5 h/night during intervention reduced their BMI by nearly 4 %, a comparable decrease in the BMI was found neither in subjects who slept more than 7.5 h nor after relaxation training independent of sleep duration. Sleep duration itself did not change in any group. Although results should be interpreted with caution due to the small sample size, this is the first study to indicate that physical exercise might compensate for disturbed body weight regulation associated with short sleep duration.