Effects of Weight Reduction on Sleep and Alertness in Long-distance Truck and Bus Drivers

Inclusion Criteria: * male * age 30-62 years * long-distance truck or bus driver (on average continuous driving for at least one hour daily outside the city center) * irregular working hours (on average at least once weekly between 0600-1800 hours) * waist circumference at least 100 cm * sedentary: leisure physical activity no more than 30 minutes twice weekly at moderate intensity, and no medical contraindications to increase physical activity Exclusion Criteria: * no moderate or severe sleep apnoea with CPAP therapy or with previous surgical operations in the neck area (e.g., UPPP) * no regular use of sleeping medicines (on average not more often than once weekly) * no severe sleep disorder * greatly elevated resting blood pressure (\> 180/120 mmHg) * no diabetes mellitus with medication