Testosterone and the heart
Testosterone is responsible for men's deep voices, increased muscle mass, and strong bones. It also has crucial effects on male behavior, contributing to aggressiveness, and it is essential for the sex drive and normal sexual performance.
Although testosterone acts directly on many tissues, some of its least desirable effects don't occur until it is converted into another male hormone, dihydrotestosterone (DHT). DHT acts on the skin, sometimes producing acne, and putting hair on the chest but often taking it off the scalp. DHT also stimulates the growth of prostate cells, producing normal growth in adolescence but contributing to benign prostatic hyperplasia (BPH).
But while testosterone's effects on many organs are well established, research is challenging old assumptions about how the hormone affects a man's heart, circulation, and metabolism.
A direct association between testosterone and heart disease has never been established, but for many years, doctors have suspected that a link exists. The reasoning goes like this: men have much more testosterone than women, and they develop heart disease about 10 years before their female counterparts. Like other muscle cells, cardiac muscle cells have receptors that bind male hormones. Animals that are given testosterone develop enlarged hearts. Athletes who abuse testosterone and other androgenic steroids have a sharply increased risk of high blood pressure, heart attack, and stroke. And in high doses, testosterone can have a negative effect on cardiac risk factors, including HDL ("good") cholesterol levels.
The fact that large amounts of testosterone harm the heart and metabolism doesn't necessarily mean that physiological amounts are also harmful. In fact, research is challenging these old dogmas.
It's hard for scientists to study possible new risk factors for heart disease. One reason is that there are so many cardiac risk factors, including family history, age, gender, blood pressure, cholesterol, blood sugar, obesity, smoking, exercise, and personality.
It's also hard for scientists to study testosterone. There is an exceptionally wide range of normal values. Healthy men can have testosterone levels between 270 and 1,070 nanograms per deciliter (ng/dL).
Heart disease and testosterone are mighty complex on their own, and studies that evaluate the two together are more complex still. Scientists who undertake these daunting investigations must account for all the things that influence heart disease and all the variables that affect testosterone.
With all these pitfalls, it's not surprising that more research is needed to fill in all the blanks. Still, even if current information can't tell us if testosterone can protect a man's heart, it can dispel fear that physiologic levels of the hormone are toxic.
Testosterone and cardiac risk factors
In high doses, androgens tend to raise LDL ("bad") cholesterol levels and lower HDL cholesterol levels. That's one of the things that gave testosterone its bad reputation. But in other circumstances, the situation is very different. Men who receive androgen-deprivation therapy for prostate cancer drop their testosterone levels nearly to zero, and when that happens, their cholesterol levels rise. Even within the normal range, men with the lowest testosterone levels tend to have the highest cholesterol levels.
Diabetes is another important cardiac risk factor. Prostate cancer treatments that lower levels of testosterone produce insulin resistance and increase the risk of diabetes. Obesity increases the risk of both diabetes and heart disease. Men with low testosterone have more body fat and more of the abdominal fat that's most harmful than men with higher hormone levels, but since obesity itself reduces testosterone, it's not clear which is the cause and which the effect.
Peripheral artery disease (PAD) is an important form of atherosclerosis in its own right, and it also signals an increased risk for heart disease. A Swedish study of over 3,000 men with an average age of 75 linked low testosterone levels to an increased risk of PAD. At present, the hormone does not appear linked to hypertension or inflammatory markers.
Testosterone therapy and cardiovascular function
Low testosterone levels have been linked to various cardiac risk factors, but that doesn't prove that low levels actually cause heart disease. Still, if testosterone therapy could help men with heart disease, it would bolster the argument that testosterone may be safe for the heart. Only a few small, short-term studies have been published to date, and the results offer mixed support for this theory.
As men age, it's not just heart disease they need to worry about. They also begin to lose muscle mass and bone density; red blood cell counts sag; sexual ardor declines; mood, energy, and memory drift down; and body fat increases. In theory, at least, testosterone therapy might blunt or reverse each of these woes. But the theoretical benefits should be balanced against the theoretical risks.
The most serious long-term complications of testosterone therapy include an increased risk of benign prostate disease (BPH). Although some doctors worry that testosterone treatments might increase the risk of prostate cancer, the evidence for this is small. Indeed, there is evidence that men with low testosterone levels (who therefore might benefit from testosterone treatment) have a higher risk of developing prostate cancer.
Do the potential gains of testosterone treatment outweigh the possible pains? Nobody knows. To date, only small, short-term studies have been completed. More research is needed to learn how testosterone affects the heart and the rest of a man's body and mind.
The best advice is to protect your heart and your body by taking care of known risk factors, such as cholesterol, blood pressure, diabetes, obesity, and tobacco exposure. And don't forget that diet and exercise remain the keys to reducing the risk of heart disease.
April 2010 update