Cutting back on sleep drastically lowers testosterone levels in young male adults. Less than five hours a night of sleep had significantly lower levels of testosterone than controls. After just one week of less than five hours a night of sleep resulted in a 10-15% decrease in testosterone levels.
Low levels of testosterone lead to low energy, reduced libido, poor concentration, and fatigue. Prolonged low levels lead to osteoporosis, loss of muscle volume and strength, and increased risk for heart disease.