Testosterone is best known as the hormone that increases sex drive—in both animals and humans. In male song birds during breeding season, increased testosterone—and its conversion into estrogen—causes an increase in volume of several song control nuclei within the bird’s brain, a mechanism designed to catch the female’s attention.

In humans, testosterone also drives the male’s pursuit of the female. Furthermore, testosterone is important in the proper functioning of sexual organs and maintaining an erection. But while testosterone is best known as a male sex hormone, it also possesses properties thought to influence a wide range of health conditions in both males and females.

In fact, new research indicates this hormone may prevent Alzheimer’s disease and alleviate depression in men. The testosterone precursor, androstenediol, also has been found to be low in women who suffer from Sjögren’s Syndrome.

Testosterone and Alzheimer’s
Two studies published in the January 27 edition of Neurology indicate that free testosterone levels—i.e., testosterone not bound to sex hormone binding globulin (SHBG)—are lower in men who later develop Alzheimer’s disease. In the two current studies, researchers sought to further explore whether low testosterone levels are actually a cause of Alzheimer’s disease or merely a consequence of the disease itself.

In one study, they examined data from 574 men (32 to 87 years old) who were free of Alzheimer’s at the study’s start. In the average follow-up period of 19.1 years, 54 subjects were diagnosed with Alzheimer’s.1 The researchers in this study looked at what’s known as the free testosterone index (FTI), calculated by dividing serum testosterone by sex hormone-binding globulin. The study’s authors determined that the higher the FTI, the lower the risk of developing Alzheimer’s. With each 10-unit increase in FTI, there was a 26 percent reduction in Alzheimer’s risk, indicating that free testosterone does protect against the development of Alzheimer’s and that low free testosterone levels are not merely a consequence of Alzheimer’s but rather a cause of the disease.

In the other study, Italian researchers examined 32 men and 64 women with Alzheimer’s and compared these subjects�?testosterone levels with those in 32 men and 72 women free of Alzheimer’s. In subjects with Alzheimer’s, sex hormone-binding globulin levels were significantly higher and the FTI was significantly lower. These high levels of sex hormone-binding globulin indicate that testosterone in these patients is not as bioavailable as in subjects who do not have Alzheimer’s and who have lower levels of sex hormone-binding globulin.2

Antidepressant Actions
In addition to its other roles in the body, testosterone may play an important part in well-being. At least 30 percent of men over the age of 55 are thought to be testosterone-deficient. This deficiency is associated with decreased muscle mass, bone mineral density, and libido, and with anorexia, fatigue, and irritability. A new study indicates testosterone deficiency may be associated with depression as well.

Researchers studied the medical records of 278 men 45 years and older who did not have prior diagnosed depressive illness and who had either consistently normal or low testosterone levels at the study’s start and during two years�?follow-up. During the study, 23 men were found to have low testosterone levels. Roughly 22 percent of the subjects with low testosterone levels developed depressive illness compared to only about seven percent of the subjects with normal testosterone levels. Men with low testosterone also developed depression in less time than the men with normal testosterone levels who developed depression.

According to the researchers, testosterone levels may be linked to depression because symptoms of low testosterone—fatigue, muscle loss, etc.—may trigger the feelings of despondency. Low testosterone levels also may actually be the cause of depression and the associated symptoms.3

Sjögren’s Syndrome
Sjögren’s Syndrome is a slowly progressive auto-immune disease that usually occurs in menopausal women. Sjögren’s Syndrome is characterized by dry eyes and mouth and recurrent salivary gland enlargement. Emerging evidence indicates that women who suffer from this condition are deficient in androstenediol, a precursor to testosterone. Like testosterone, androstenediol belongs to a group of male hormones known as androgens. Androgens help regulate tear glands as well as meibomian (tarsal) glands in the eyelid that secrete a sebaceous substance that prevents the lids from sticking to the eye.

Because Sjögren’s Syndrome is characterized by dry eyes, researchers at Harvard Medical School theorized that people who suffer from this disease are deficient in androgens compared to age-matched controls. The researchers discovered that although female subjects with Sjögren’s Syndrome were not deficient in testosterone per se, they did have low levels of other androgens, including the testosterone precursor androstenediol as well as dehydroepiandrosterone (DHEA), which can be converted into testosterone. They also had low levels of dihydrotestosterone (DHT), compared to controls. The researchers concluded that the androgen deficiency seen in women with Sjögren’s Syndrome may contribute significantly to the development of dry eyes in this disorder. 4

References
1. Moffat SD, Zonderman AB, Metter EJ, Kawas C, Blackman MR, Harman SM, Resnick SM. Free testosterone and risk for Alzheimer’s disease in older men. Neurology. 2004 Jan 27; 62(2): 188-93.
2. Paoletti AM, Congia S, Lello S, Tedde D, Orru M, Pistis M, Pilloni M, Zedda P, Loddo A, Melis GB. Low androgenization index in elderly women and elderly men with Alzheimer’s disease. Neurology. 2004 Jan 27; 62(2): 301-3.
3. Shores M, Sloan K, Matsumoto A, Moceri V, Felker, B, Kivlahan D. Increased Incidence of Diagnosed Depressive Illness in Hypogonadal Older Men. Arch Gen Psychiatry. 2004;61:162-167.
4. Sullivan DA, Belanger A, Cermak JM, Berube R, Papas AS, Sullivan RM, Yamagami H, Dana MR, Labrie F. Are women with Sjogren’s syndrome androgen-deficient? J Rheumatol. 2003 Nov;30(11):2413-9.