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Testosterone deficiency, or "low T," has become well known as the cause of drooping interest in sex and sagging waistlines in middle-aged and older men. But a new study finds that low estrogen may be a problem for middle-aged men, too.

Unexpected findings of new research reported in the New England Journal of Medicine suggest that "manopause," or male menopause, may be caused not just by declining testosterone but also by declining estrogen.

Testosterone is typically considered the "guy homrone," and estrogen is typically considered the primary hormone in women. Both hormones, however, appear in both sexes, just in vastly Differing amounts.

Men's bodies produce more testosterone but some estrogen, all of it in the form of estrogen known as estradiol. Women's bodies producing more estrogen, in more forms, but also some tesosterone.

The recent study, conducted at Harvard University, found that estrogen levels are important in men, too.

"Low T" Leads to "Low E" in Men

Scientists recruited 400 healthy men aged 20 to 50. For four months, they gave the men injections of a drug called Zoladex (goserelin), which stops the production of testosterone. They also gave the men four levels of testosterone replacement therapy, ranging from placebo (no testosterone) at all to complete testosterone production. Additionally, half the men got shots that prevented the conversion of testosterone into estrogen, and half did not.

The men in the study had a variety of testosterone and estrogen levels ranging from essentially zero to normal. The researchers found that:

  • Testosterone is more important for maintaining muscle.
  • Estrogen is more important for regulating body fat.
  • Both hormones are important for sexual desire.

The men who had estrogen production completely blocked reported problems with severe hot flashes.

A Vicious Cycle of Hormone Deficiency and Obesity

It was already well known that testosterone levels go down as men age. It was also well known that estrogen levels can go up in obese men, because fat cells contain an enzyme that converts testosterone into estrogen. And it was also known that men tend to have problems with erectile dysfunction about the time they start putting on lots of weight. But why?

In overweight and obese men, fat cells turn testosterone into estrogen and estrogen encourages the growth of fat, especially on the buttocks. Declining testosterone and increasing estrogen levels can become a vicious cycle when men become seriously overweight.

What's new in this study? It turns out that even before men start fighting their middle aged spread and have to deal with lagging energy in the bedroom, low estrogen levels can become a problem. 

The problem isn't just that fat cells are "burning up" testosterone. It can also be that a man's body isn't producing enough estrogen so he gains weight, at least at first. High estrogen levels are a problem in weight gain, but it turns out that low estrogen levels are also a factor in putting on the pounds.

Are Doctors Going to Start Treating "Low E?"

You can't watch a sports match on American television without seeing ads for testosterone replacment patches to treat "low T." Does this mean that now we will be seeing ads for prodcuts for "low E" as well?

Dr. Abraham Morgentaler of Harvard University told CBS News that the study does not suggest that men who are deficient in estrogen will start needing to get estrogen replacement therapy. Fortunately, Morgentaler says, if a man gets testosterone, he also gets the needed estrogen. Estrogen pills for men are not on the horizon.

What's different is when men will start getting testosterone replacement. Normal-weight men who had low testosterone levels put on fat. Normal-weight men who had both low testosterone levels and low estrogen levels put on even more. Muscle loss didn't occur testosterone levels were below 200 nanograms, but fat gain started when testosterone levels were between 300 and 350 nanograms.

Since doctors previously didn't have a good clinical reason for prescribing testosterone replacement when men's testosterone levels were low, about 300 to 350, but not so low that muscle low would occur, around 200, many men with borderline testosterone deficiency did not get treatment. Now that it is known that the vague symptoms of low T and low E in men begin when testosterone levels fall below 350, more men will get testosterone replacement therapy.

  • Finkelstein JS, Lee H, Burnett-Bowie SA, Pallais JC, Yu EW, Borges LF, Jones BF, Barry CV, Wulczyn KE, Thomas BJ, Leder BZ. Gonadal steroids and body composition, strength, and sexual function in men. N Engl J Med. 2013 Sep 12. 369(11):1011-22. doi: 10.1056/NEJMoa1206168.
  • Photo courtesy of seikihan on Flickr: www.flickr.com/photos/sekihan/6345542330

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