Does a naturally declining testosterone level cause the signs and symptoms of aging?

Not necessarily. Men can have many signs and symptoms as they age. Some that might occur as a result of lower testosterone levels can include:

• Changes in sexual function. This might include reduced sexual desire, fewer spontaneous erections — such as during sleep — and infertility.
• 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 body hair loss are possible. You might have less energy than you used to.
• Emotional changes. Low testosterone can contribute to a decrease in motivation or self-confidence. You might feel sad or depressed, or have trouble concentrating or remembering things.

Some of these signs and symptoms can be caused by other factors, including medication side effects, obstructive sleep apnea, thyroid problems, diabetes and depression. It's also possible that these conditions cause low testosterone levels, so treatment might result in increase of testosterone levels.

A blood test is used to diagnose a low testosterone level.