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As men age, circulating free testosterone decreases as they produce less testosterone while producing more estradiol (an estrogen found in men). Every man will experience a decrease in "bioavailable" testosterone, but for reasons still unknown, some men’s hormone levels drop lower than others.
A man whose total blood serum testosterone levels fall below 300 nanograms per deciliter has a high likelihood of experiencing hypogonadal symptoms. Free testosterone levels below 5.0 picograms per milliliter can also trigger symptoms. Psychological stress, alcohol, injuries or surgery, medications, obesity and infections can also contribute to its onset.
Low testosterone (hypogonadism) can be caused by many factors, all of which play out against the normal steady decline in testosterone levels with age. Tumors on the pituitary gland (which controls testosterone production in the testicles), problems with the testicles themselves, injury, infections, and being overweight can all cause testosterone levels to drop below normal. Excess body fat does this because testosterone is normally broken down in the body's fat cells; hence if you have a lot of fat, your body breaks down testosterone extra-quickly, leading to a deficiency. And abdominal or "belly" fat has a greater capacity to convert testosterone to estrogen than other types of fat.
Another risk factor for hypogonadism that has only recently come to light is diabetes. A strong relationship has been discovered between impaired glucose tolerance, which is a cardinal feature of diabetes, and low testosterone levels. It appears that the high blood sugar levels and/or low insulin levels characteristic of diabetes harm the cells in the testicles that are responsible for making testosterone. A study of 221 middle-aged men confirmed this finding: The men most likely to be diabetic also had the lowest testosterone levels.
Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.