From this article on recent research on male menopause. Researchers at the University of Manchester in England examined the testosterone levels of nearly 4,000 men between the ages of 40 and 79, and the volunteers answered questions about their mental, physical and sexual health for the study, published in the New England Journal of Medicine. Among the symptoms associated with low testosterone levels were low levels of sexual desire, erectile dysfunction and poor morning erection, along with fatigue and depression. Yet some symptoms that the men reported experiencing, like poor concentration, feelings of worthlessness and anxiety, were not linked to low testosterone levels. Low testosterone levels also were associated with obesity and poor general health.