Many men, as they get older, lose their sex drive; this may be associated with increased fatigue and sometimes depression. If their testosterone level is low, they are often treated with this hormone, in one form or another. But there are some risks (real or apparent) to the use of testosterone, so an alternative effective treatment would be very welcome.
A group of Italian researchers have studied carnitine as a possible substitute, and have reported their findings in the journal Urology. Propionyl-l-carnitine and acetyl-l-carnitine are powerful antioxidants that have proved beneficial in diseases typical of aging (e.g. Alzheimer's, peripheral artery disease), according to some reports. Here's a summary of their study.
What was done?
A total of 150 men aged 60 to 74 (average age: 66) were allocated randomly to one of three groups. They had to have decreased libido and erectile quality, depressed mood and ability to concentrate, irritability, fatigue, and a free testosterone level below 6 pg/mL. They were not accepted if they had prostatic enlargement, a raised PSA (prostate-specific antigen, a marker for prostate cancer), smoked or drank alcohol, had diabetes, a previous MI, or other possibly relevant diseases.
The first group was given testosterone undecanoate (160 mg/day), the second group propionyl-l-carnitine plus acetyl-l-carnitine (2 g/day of each), and the third group was given starch tablets (as a placebo). The treatment period was 6 months.
A battery of lab tests and questionnaires were conducted before, during (at 3 and 6 months) and 6 months after the treatment. They covered cardiovascular strength, sex drive, sexual satisfaction, hormone levels in the blood, prostate size, PSA level, mood (using the Hamilton Depression Scale), and fatigue.
Twelve men dropped out before treatment started, when they learned that they might receive a placebo; 8 others dropped out during the study, but this was not due to any side effect of treatment. This left 130 men in the study - 40 on testosterone, 45 on carnitine, and 45 on placebo.
What was found?
Both testosterone and carnitine improved sexual performance, as shown by nocturnal penile tumescence measurements1 and the International Index of Erectile Function score; carnitine was found to be more effective than testosterone in this respect. Both treatments improved the blood flow through the arteries supplying the penis to an equal extent; these measurements had returned to baseline levels at 6 months after the end of treatment.
Testosterone has the reputation of increasing prostate size. This was confirmed here - the testosterone treatment group had increased prostatic volume at 3 and 6 months, which returned to normal after 6 months' off treatment. At the same time, LH (luteinizing hormone) levels were lowered. PSA levels were unchanged. Carnitine had no effect on prostate volume, LH, or PSA levels.
Both testosterone and carnitine significantly improved the symptoms of depression and fatigue, as measured by questionnaires. The side effects reported were negligible, and were the same in each treatment group.
What does this mean?
In this study design, both testosterone and carnitine were effective in improving the symptoms reported by some aging males. Carnitine was superior to testosterone in their action on early symptoms of impotence, but otherwise their effects were roughly equal. Testosterone was associate some degree of prostate enlargement, but carnitine was not.
Does this mean aging men should consider carnitine rather than testosterone for their problems? There are reasons for caution. First, the mechanism of action of carnitine is not clear. The authors of the report state that the reason other antioxidants (such as vitamin E, tocopherol, or glutathione) don't work in aging men - while carnitine does - is because they have a different point of attack in the biochemical processes. The rationale for using testosterone, on the other hand, is clear.
Second, carnitines (acetyl-l- and propionyl-l-carnitine) have been investigated for several years in several conditions: poor semen quality leading to infertility, Peyronie's disease (bent shaft of penis), peripheral arterial disease, and Alzheimer's disease. In none of these conditions has carnitine proved to be an effective treatment in "adequate, well-controlled clinical studies" - the FDA criterion for efficacy and safety of a new drug. See the third link below, which takes a cool look at the likely benefits of carnitine.
Clearly we need another well-controlled study, rather than basing a new treatment on the results of this study alone. We can hope that this will be done soon, and that the results confirm carnitine's superiority to the potentially risky use of testosterone in older men. Otherwise, we must conclude that this study is just another false alarm in the history of carnitine research.
* Carnitine versus androgen administration in the treatment of sexual dysfunction, depressed mood, and fatigue associated with male aging. G. Cavallini, S. Caracciolo, G. Vitali, et al., Urology, 2004, vol. 641, pp. 641--646
Summarized by Robert W. Griffith, MD
July 16, 2004