ZMA makers claim that increasing these three nutrients in your system can build muscle strength and stamina, speed muscle recovery, and improve the quality of your sleep.
But there’s not a lot of research to back that up.
In 2000, researchers gave ZMA supplements to a group of NCAA football players working out twice a day. After 7 weeks, they found a significant increase in the players’ testosterone and growth hormone, both of which are linked to muscle growth. However, one of the scientists who conducted the study holds the registered trademark for the original formula of ZMA, and his company funded the research.
Further experiments done by other scientists haven’t duplicated the same effects. In fact, there’s no additional research that ZMA aids athletic performance or weight loss.
Because of that, the International Society of Sports Nutrition has declared ZMA’s effect on muscle building “not known,” and the Australian Institute of Sport, which informs athletes about supplements, has decided that ZMA is lacking clear proof of benefits. There are no similar supplement-rating organizations in the U.S.
No major side effects of ZMA have been reported, but there could be health concerns if the supplements are taken more frequently than the manufacturer suggests.
Too much zinc or magnesium can cause diarrhea, nausea, and cramping, and when taken in high doses over a period of time, zinc can lower the body’s immunity and its levels of HDL, or “good,” cholesterol. One study also found that men who took 100 milligrams of zinc supplements for 10 years were more likely to get prostate cancer, but the reason isn't clear. Taking extremely high levels of B6 for a year or more may cause nerve damage.
More immediate concerns: Zinc and magnesium can make it harder for your body to absorb some prescription medications, such as antibiotics; and B6 supplements can intensify the side effects of certain drugs.