Testosterone levels vary greatly among men. In general, however, older men tend to have lower testosterone levels than do younger men. Testosterone levels gradually decline throughout adulthood, about 1 percent a year after age 30 on average.

Recognizing Low Testosterone Levels
A blood test is the only way to diagnose a low testosterone level or a reduction in the bioavailability of testosterone. Some men have a lower than normal testosterone level without signs or symptoms. In this case, no treatment is needed. For others, low testosterone might cause:

Changes In Sexual Function: This might include erectile dysfunction, reduced sexual desire, and fewer spontaneous erections such as during sleep and infertility. Your testes might become smaller as well.

Changes In Sleep Patterns: Sometimes low testosterone causes sleep disturbances, such as insomnia, or increased sleepiness.

Physical Changes: Various physical changes are possible, including increased body fat; reduced muscle bulk and strength; and decreased bone density. Swollen or tender breasts (gynecomastia) and loss of body hair are possible. Rarely, you might experience hot flashes and have less energy.

Emotional Changes: Low testosterone might contribute to a decrease in motivation or self-confidence. You might feel sad or depressed, or have trouble concentrating or remembering things.

However, some of these signs and symptoms can be caused by underlying factors other than low testosterone, including medication side effects, thyroid problems, depression and excessive alcohol use. There are also conditions, such as obstructive sleep apnea, that might affect testosterone levels. Once these conditions are identified and treated, testosterone typically will return to a normal level.