A number of disorders and therapies can lead to male hypogonadism (low blood levels of testosterone, the major male sex hormone). Symptoms of hypogonadism include erectile dysfunction and reduced libido.
Also associated with hypogonadism are osteoporosis, loss of body hair, increased body fat, and decreased muscle mass and strength. These manifestations of hypogonadism can and should be reversed by administration of testosterone.
More controversial is what to do about the gradual decline in testosterone levels found in healthy men as they grow older. A European study of 10,423 men, published recently in the journal Circulation, compared men who had the lowest testosterone levels with those who had higher testosterone levels.
The study showed that the men with the highest levels had a 41 percent lower risk of death from any cause, a 47 percent lower risk of dying from cardiovascular disease (CVD), and a 29 percent lower risk of death from cancer.
Although the apparent protection against cancer conferred by higher testosterone levels is difficult to explain, the decreased risk of CVD deaths confirms the results of earlier studies and fits with the risk factors linked to low testosterone, such as elevated blood pressure, higher total and low-density lipoprotein (LDL) cholesterol and triglycerides, and lower protective HDL cholesterol.
Other studies showed that men with low testosterone have greater calcification and stiffness of the aorta and more rapid progression of atherosclerosis in the carotid arteries.
Given the increased amounts of body fat in men with lower testosterone, it is not surprising that they also have a greater likelihood of another major risk factor for CVD — type 2 diabetes.
These findings must be confirmed by more studies but they raise an important question: Should healthy older men with declining testosterone levels be treated with testosterone replacements?
Testosterone supplements have been shown to reduce body fat and increase muscle mass. However, the effects of testosterone supplements on a man's chances of developing type 2 diabetes and on other risk factors for CVD remain unknown.
For the present, I believe caution is in order regarding testosterone replacement in healthy men with lower testosterone levels. Great care must be taken not to draw too many conclusions from population studies, which merely compare data points among different groups.
A controlled clinical trial called the Women's Health Initiative, for example, did not find that estrogen replacement reduced the risk of CVD, as had been predicted by population studies like the one published in Circulation.
So, it appears that a large, controlled trial of testosterone replacement is needed to answer this question, just as such trials have been necessary to decide what to do about the results of other population studies.