Supplements to boost immune system

Vitamin D and zinc may help support immune function, and glutamine may be worth considering, though its evidence is limited. Echinacea has uncertain benefits and potential downsides.

• Vitamin D: 1,000–2,000 IU daily is described as probably safe for most people. Blood testing can show whether you need more and help avoid excessive dosing; some people may need higher amounts. 1 2
• Zinc: The episode discusses 100 mg or more for helping combat colds, while cautioning that it can cause stomach upset. Take it with a meal rather than on an empty stomach. 3
• Glutamine: It may support immune-cell activation, but the human evidence is limited; one discussion describes a lower incidence of respiratory infections among heavily training endurance athletes taking it. Glutamine is also available from food, including cottage cheese. 4 5
• Echinacea: Evidence that it prevents colds or flu is weak. High, regular doses may impair aspects of innate immunity, so the suggested approach is brief, occasional use rather than taking it continuously or for more than four weeks. 6