Reference(s)

Vit C: http://www.nhs.uk/Conditions/vitamins-minerals/Pages/Vitamin-C.aspx

Zinc: http://www.nhs.uk/conditions/vitamins-minerals/pages/other-vitamins-minerals.aspx#zinc

Vit E: http://www.nhs.uk/Conditions/vitamins-minerals/Pages/Vitamin-E.aspx

Omega 3: http://www.askdrsears.com/topics/feeding-eating/family-nutrition/foods-to-boost-immunity/foods-that-boost-your-immune-system

A study found that children taking a half teaspoon of flax oil a day experienced fewer and less severe respiratory infections and fewer days of being absent from school. The omega-3 fatty acids in flax oil and fatty fish (such as salmon, tuna, and mackerel) act as immune boosters by increasing the activity of phagocytes, the white blood cells that eat up bacteria. (Perhaps this is why grandmothers used to insist on a daily dose of unpalatable cod liver oil.) Essential fatty acids also protect the body against damage from over-reactions to infection. When taking essential fatty acid supplements, such as flax or fish oils, take additional vitamin E, which acts together with essential fatty acids to boost the immune system. One way to get more omega-3 fatty acids in your diet is to add one to three teaspoons of flax oil to a fruit and yogurt smoothie.