Fortified Orange Juice
Although I am not a fan of drinking fruit instead of eating it, the immune boost offered by fortified orange juice is hard to surpass.
One cup contains 100% of the Daily Value for vitamin C, a critical antioxidant required for proper immune system function, plus 25% of the Daily Value for vitamin D.
This is critical since most individuals have vitamin D deficiency, which makes them more prone to disease.
Supplements also may help prevent respiratory infections, according to 2017 research.