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Vitamin T for Sex

Hot, hot hormones.

Behavior Drives Hormones, Not Vice Versa

For argument's sake, let's suppose that for every smidgen of a decline in testosterone, there was a proportional decline in sexual drive, energy, and libido, while for every smidgen of a rise, there was an increase. If that were the case, researchers should be able to select a group of normal, healthy guys for a study, measure their testosterone levels, and show that the men with the higher testosterone levels are more libidinous, sexually active, or more aggressive.

Indeed, some studies have suggested such a correlation. But there turns out to be a confounding factor: Acting aggressively and having sex both raise testosterone levels, so the correlation seems due to behavior driving the hormones, rather than the other way around. This phenomenon has been discussed in many leading texts on the subject.

When experiments control for those factors -- acting aggressively and having sex -- the vast majority of studies, whether of humans or animals, show that individual differences in testosterone levels across the normal range don't particularly predict individual differences in aggressiveness or sexual activity. My own study, "Testicular function, social rank, and personality among wild baboons," published in the journal Psychoneuroendocrinology (Vol. 16, No. 4, 1991), is among the many to have found this.

A Mere 15% of Normal Is Enough

Here is the critical point: Give Sullivan replacement testosterone so that his circulating levels return to 15% of normal, 100% of normal, or 150% of normal, and you will have roughly the same effect in all cases. The best single review on this subject is "Behavioral effects on androgens in humans," published in the August 1996 issue of the American Journal of Psychiatry. Over a very wide range, testosterone has pretty much the same effect on behavior. Push levels below that range (due to castration or any of a number of diseases), and physiology and behavior change. Push levels above that range, by abusing anabolic steroids, and you'll typically boost aggression, perhaps libido as well. But within that broad range -- from 15% to 150% of normal -- behavior and libido remain roughly the same.

Increases Body Mass, Not Sex Drive

So what CAN extra testosterone do? A few studies, including one in the October 1992 issue of the Journal of Clinical Endocrinological Metabolism, have shown that boosting testosterone levels in aged males increases body mass and decreases cholesterol levels. Sullivan, who experienced a 20-pound weight gain, can now squat more than 400 pounds and feels a surge of energy "less edgy than a double espresso but just as powerful."

However, there have been no double-blind studies showing that supplemental testosterone reinstates "youthful" sexual performance or libido, alertness, or energy.

And the testosterone experts agree. Consider the following summary from a recent review published in the July 2000 issue of the journal Geriatrics: "Hormones such as DHEA, human growth hormone, and testosterone tend to decline with aging, but the therapeutic value of [restoring] them to 'normal' physiologic levels has not been substantiated by controlled clinical trials." Furthermore, Williams' Textbook of Endocrinology (1998, 9th edition), essentially the "bible" of the field, states that "The decline in male sexual function with age does not appear to be endocrine-mediated."

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