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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Man to Man Man to Man

Testosterone -- The 'Heart' of the Matter

September 14, 2014

By Harvey B. Simon M.D.

Harvard Medical School

Forget clothes. In a very real sense, testosterone makes the man. It:

  • Gives us the deep voice, large muscle mass and strong bones that characterize our gender
  • Stimulates the production of red blood cells by the bone marrow
  • Contributes to aggressiveness
  • Is essential for the libido or sex drive, as well as for sexual performance
  • Stimulates the growth of the genitals at puberty and helps produce sperm
  • Can lead to acne, put hair on the chest — or take it off the scalp — after the hormone is converted to dihydrotestosterone (DHT)

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.

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What We Know

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:

  • Animals 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
  • In high doses, testosterone can raise LDL ("bad") cholesterol and lower HDL ("good") cholesterol levels

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.)

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Testosterone Tinkering

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 doctors wrote prescriptions for testosterone to more than 2 million American men in 2013. That's double the number of men taking the drug over a 3 year period. Why are all these men taking testosterone? And should they?

As the years pile on, men experience declines in:

  • Muscle mass and bone density
  • Red blood cells
  • Sexual desire
  • Mood
  • Energy
  • Memory

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 new study results suggest that these potential benefits have been overstated. The medical evidence so far does not support the use of testosterone as therapy to slow down changes related to aging.

Testosterone Therapy Risks

The most worrisome risks of testosterone therapy are heart attack, stroke and blood clots. Studies in the past produced conflicting results. More recent studies have suggested testosterone therapy does increase the risk of heart attack and stroke in the men that are using it the most – middle aged and older men. The risk appears even higher for smokers and men with high blood pressure and high cholesterol.

This year reports of another potential life-threatening problem have emerged. Some men using testosterone are developing blood clots in leg veins. This is called deep vein thrombosis.

These blood clots can break off and go the lungs. Doctors call this a pulmonary embolism. When the clots reach the lungs, they cause chest pain and shortness of breath. Large blood clots in the lungs can be deadly.

The U.S. Food and Drug Administration told drug companies to add a warning on testosterone product labels about the risk of these blood clots.

Another long-term risk of testosterone therapy is enlargement of the prostate gland. Doctors call it benign prostatic hyperplasia (BPH). Other potential side effects include a possible increased risk of prostate cancer, 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.

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The Bottom Line

So, what's a guy to do? Unless you clearly have an abnormally low testosterone level (hypogonadism), it’s time to reconsider the benefit-risk balance of testosterone therapy. If you already are using testosterone, you don’t need to immediately stop. Discuss it with your doctor at your next visit.

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:

  • Lowering heart-disease risk
  • Shedding body fat
  • Building up muscles and bones
  • Improving memory, mood and vigor
  • Sslowing the aging process

Testosterone makes the man, but a good lifestyle makes him healthy.

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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.


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