The term amino acid might sound a bit strange, but the definition is straightforward: Strands of these molecules form the building blocks of protein. When you digest protein, your body breaks it down into individual amino acids and then reconstitutes them as needed.

Amino acid supplements are most often associated with bodybuilders. After all, muscle consists of protein, and amino acids do help build muscle, and not just in young men. But individual amino acids also serve a variety of health-promoting roles in the body.

For example, they can influence mood, reduce stress and boost immunity. As a consequence, gym goers should be mindful of what they hope to achieve by taking an amino acid. As supplements go, their quality is exceptional. “Amino acid supplements are highly specific in their effects,” says Tod Cooperman, MD, president of, which independently evaluates the quality of supplements. “Our analyses have generally found higher quality among amino acid supplements than among other types of supplements.”

As a general rule, take amino acid supplements on an empty stomach.

1. Muscle maker.

By middle age, you rapidly lose muscle mass, even if you exercise. You can counter some of this loss by taking branched-chain amino acids (BCAAs)—leucine, isoleucine and valine. Of these, leucine is by far the most important for making new muscle, and a recent analysis of nine studies confirmed its muscle-enhancing effect. Leucine works for seniors, too, who might actually benefit the most. Adding vitamin D and exercising amplifies the benefits.

2. Mood lifter.

Amino acid L-tryptophan and 5-hydroxytryptophan (5-HTP) form the key building block of serotonin, the neurotransmitter that protects against anxiety and depression. Supplements have been found helpful for these disorders, as well as with insomnia.

Dose: Take either 500 mg of L-tryptophan or 50 mg of 5-HTP three times daily.

3. Stress buster.

The amino acid gamma- aminobutyric acid, or GABA, functions as a neurotransmitter that promotes a relaxed feeling while also increasing mental focus. It works by helping the brain tune out distracting “background noise.” A 2015 study by Dutch researchers found GABA supplements improve decision making and reaction times. Theanine, an amino acid found in high-quality green tea, boosts the brain’s alpha waves, which can reduce anxiety. GABA and theanine may be taken together.

4. Immune strengthener.

The preferred form of the amino acid cysteine, N-acetylcysteine (NAC) is an essential building block of glutathione, the body’s principal antioxidant. An Italian study found that NAC supplements greatly reduced flu symptoms among seniors. Its side benefits include supporting the liver’s detox efforts and lung function.

5. Blood-vessel toner.

L-arginine functions as the precursor to nitric oxide, a compound that regulates blood-vessel flexibility. Increased flexibility is good for the cardiovascular system, and some research indicates that this amino acid can lower blood pressure. Men also need healthy blood-vessel tone for erections, and arginine may help men with erectile dysfunction, as well. Some research has also found that a combination of arginine and the herb yohimbe might increase blood flow to the vagina, which can increase arousal and help women achieve orgasm.