Alcohol Impairs Reproductive Functions

ALCOHOL ALERT: National Institute on Alcohol Abuse and Alcoholism No. 26 PH 352 October 1994

The human reproductive system is regulated by many hormones. The most important are androgens (e.g., testosterone) and estrogens (e.g., estradiol). They are synthesized mainly by the testes and the ovaries and affect reproductive functions in various target tissues. Other reproductive hormones are synthesized in the hypothalamus and pituitary. Although men and women produce many of the same hormones, their relative concentrations and their functions vary.

In men, reproductive hormones are responsible for sexual maturation, sperm development and thus fertility, and various aspects of male sexual behavior. In women, hormones promote the development of secondary sexual characteristics, such as breast development and distribution of body hair; regulate the menstrual cycle; and are necessary to maintain pregnancy. Chronic heavy drinking can interfere with all these functions. Its most severe consequences in both men and women include inadequate functioning of the testes and ovaries, resulting in hormonal deficiencies, sexual dysfunction, and infertility .

Alcohol is directly toxic to the testes, causing reduced testosterone levels in men. In a study of normal healthy men who received alcohol for 4 weeks, testosterone levels declined after only 5 days and continued to fall throughout the study period . Prolonged testosterone deficiency may contribute to a "femininization" of male sexual characteristics, for example breast enlargement .

In addition, animal studies have shown that acute alcohol administration affects the release of hormones from the hypothalamus and pituitary . Even without a detectable reduction of testosterone levels, changes in these hormones can contribute to the impairment of male sexual and reproductive functions. Alcohol also may interfere with normal sperm structure and movement by inhibiting the metabolism of vitamin A, which is essential for sperm development.

In premenopausal women, chronic heavy drinking can contribute to a multitude of reproductive disorders. These include cessation of menstruation, irregular menstrual cycles, menstrual cycles without ovulation, early menopause, and increased risk of spontaneous abortions. These dysfunctions can be caused by alcohol's interfering directly with the hormonal regulation of the reproductive system or indirectly through other disorders associated with alcohol abuse, such as liver disease, pancreatic disease, malnutrition, or fetal abnormalities.

Although most of these reproductive problems were found in alcoholic women, some also were observed in women classified as social drinkers, who drank about three drinks per day during a 3-week study. A significant number of these women had abnormal menstrual cycles and a delay or lack of ovulation.

Alcohol also affects reproductive hormones in postmenopausal women. After menopause, estradiol levels decline drastically because the hormone is no longer synthesized in the ovaries, and only small amounts are derived from the conversion of testosterone in other tissues. This estradiol deficiency has been associated with an increased risk for cardiovascular disease and osteoporosis in po stmenopausal women. Alcohol can increase the conversion of testosterone into estradiol. Accordingly, postmenopausal women who drank were found to have higher estradiol levels than abstaining women. Studies have shown that in postmenopausal women, three to six drinks per week may reduce the risk of cardiovascular disease without significantly impairing bone quality or increasing the risk of alcoholic liver disease or breast cancer.