Forget clothes. In a very real sense, testosterone makes the man. It:
DHT also stimulates the normal growth of prostate cells in adolescents but contributes to benign prostatic hyperplasia (BPH) — and perhaps prostate cancer — in many older men.
So while these effects on the body are well-known, new research is challenging old assumptions about how the hormone affects a man's heart, circulation and metabolism.
For years, doctors have worried about a link between testosterone and heart disease. This is largely because men have much more testosterone than women, and they develop heart disease about 10 years before women. But we also know that:
There is no doubt that high doses of testosterone are bad for the heart and for cholesterol levels. But what about normal doses?
When doctors from the Mayo Clinic recently reviewed 30 clinical trials of normal-dose testosterone replacement therapy, they did not find any overall effect of hormone treatment on cholesterol levels, for better or worse. (Men who have a testosterone deficiency — called hypogonadism — are given replacement therapy. This condition can be due to genetic errors, mumps, severe trauma, alcoholism, cancer chemotherapy and radiation, and other, less common conditions.)
We have less information about how testosterone affects other heart disease risk factors. But it doesn't appear linked to diabetes, obesity, hypertension, heart-harmful inflammation or high levels of homocysteine (an amino acid linked to heart disease and stroke).
Just because large doses of testosterone harm the heart and metabolism doesn't necessarily mean that normal amounts are also harmful. Is it possible that testosterone therapy could help men with heart and blood vessel disease?
Only a few small, short-term studies so far suggest any answers, and their results are mixed.
The real question is whether testosterone therapy can change a man's risk of having a heart attack, stroke or blood clot. Mayo Clinic scientists reviewed six trials that together included 147 men who received placebos and 161 who received testosterone for up to three years. The testosterone did not change the risk of these events for better or worse.
Testosterone deficiency (hypogonadism) affects about 6% of American men. Most are older. If the Institute of Medicine's estimates are correct, about 250,000 American men are receiving testosterone for this condition. This is the only condition for which the hormone is approved for use by the U.S. Food and Drug Administration (FDA).
But some 1.75 million prescriptions for testosterone products were written by American doctors in 2002 — at a cost of $400 million — and the numbers have continued to soar. Why are all these men taking testosterone? And should they?
Heart disease is not the only thing that's linked to aging. As the years pile on, men experience declines in:
The only thing that goes up is body fat. In theory, at least, testosterone therapy might weaken or reverse each of these woes.
This makes testosterone sound pretty good. It's why so many men are turning to the drug. But the theoretical benefits should be balanced against theoretical risks.
The most serious long-term risks of testosterone therapy are benign prostatic hyperplasia (BPH) and prostate cancer. Other potential side effects include polycythemia (an excessive number of red blood cells), sleep apnea (breathing pauses during sleep that may increase the risk of high blood pressure, heart attack and stroke), gynecomastia (benign breast enlargement), acne and liver disease.
Nobody knows if the potential gains of testosterone treatment outweigh the possible pains. To date, only small, short-term studies have been completed. They report few side effects but also few benefits.
More research is needed to learn how testosterone affects the heart and the rest of a man's body and mind. Because of the Women's Health Initiative, medical "wisdom" was turned on its ear when the large study reported that hormone replacement therapy does more harm (breast cancer, heart attacks and strokes) than good, particularly for older women. Because of the possible risks of long-term testosterone therapy, however, a "Men's Health Initiative" is not in the works.
Without good data, what's a guy to do? The best advice is to protect your heart and your body by reducing or eliminating risk factors such as cholesterol, blood pressure, diabetes, obesity and tobacco exposure.
Don't forget that diet and exercise are still the keys to:
Testosterone makes the man, but a good lifestyle makes him healthy.
Harvey B. Simon, M.D. is an Associate Professor of Medicine at Harvard Medical School and a member of the Health Sciences Technology Faculty at Massachusetts Institute of Technology. He is the founding editor of the Harvard Men's Health Watch newsletter and author of six consumer health books, including The Harvard Medical School Guide to Men's Health (Simon and Schuster, 2002) and The No Sweat Exercise Plan, Lose Weight, Get Healthy and Live Longer (McGraw-Hill, 2006). Dr. Simon practices at the Massachusetts General Hospital; he received the London Prize for Excellence in Teaching from Harvard and MIT.