Editor’s Note: Irene Lewis-McCormick is a graduate student in health and human performance. If you would like to ask her a fitness-related question, e-mail the question to [email protected].

Q: I am interested in learning more about the supplement androstenedione. What is it and how could it have helped Mark McGwire’s game?

A: “Androstenedione,” also known as “andro,” was a little known supplement until the St. Louis Cardinals’ slugger sent homerun No. 62 flying over the left-field wall.

It is within the rules for Major League Baseball players to use the supplement, although the National Football League, the National Collegiate Athletic Association and the International Olympic Committee ban this supplement.

Sales of androstenedione increased five-fold in the month following the news of McGwire’s use. The supplement “andro” has become big business among bodybuilders and athletes who are not subject to sanctions by a sports-governing body. It is readily available at most supplement retailers.

Androstenedione is a male sex hormone that is produced by the body as a precursor to testosterone. Testosterone is a hormone produced in the body that signals changes within the body, including muscle growth, hair growth and sex drive.

Testosterone plays an important role in the growth of muscles. Released by the body during exercise, testosterone helps muscle cells rebuild. Although it was initially thought to be inactive, androstenedione quickly converts to an anabolic form after it enters the body. This supplement becomes a type of steroid that is designed to increase the amount of muscle-building testosterone in the body.

This is how the process works:

• Muscle fibers are broken down by exercise.

• Testosterone reaches the muscle cells through the blood stream. Androstenedione assists in this process.

• Proteins make cells grow larger. The greater amounts of testosterone present in the muscle cells, the more protein. Thus, the muscle cells tend to grow larger.

The recommended 50-100 milligram dose increases testosterone levels up to 300 percent and lasts for about three hours. The idea is that increased testosterone production increases lean muscle mass and improves athletic performance.

However, taking androstenedione is as dangerous as taking any other anabolic steroid. Researchers believe that steroids trick the body into thinking it is older, thereby shutting off bone growth and stunting height.

Even so, because androstenedione is a supplement, it is not subject to regulation by the Food and Drug Administration.