This amino acid may be important for muscle growth, but it’s even more critical for proper immune function. Few guys realize that the immune system uses glutamine as an important fuel source, and if your levels of it drop, immune function might drop, too. Intense training can deplete glutamine levels and raise your risk of getting a cold or the flu.
Vitamin C is a potent antioxidant that offers a plethora of benefits, which include increased nitric oxide (NO) levels and enhanced fat loss. But this time of year it’s most critical function is boosting immune function. Research shows that taking high doses of vitamin C can reduce the likelihood of catching the common cold, as well as decrease the length and severity of a cold you already have.
Well known for its immune-protective properties, this herb has been shown to offer some defense against colds and the flu and can be used to protect the immune system from the stress caused by heavy training. Research shows that echinacea can also reduce the length and severity of colds and the flu. One study from the University of Connecticut reported that echinacea reduced the likelihood of developing a cold by 60% and the duration of a cold by almost two days.
This table lists several products that contain at least one of the ingredients discussed above.