Best Vitamins for Immune

All three vitamins here follow the same pattern: the strongest evidence is for correcting an actual deficiency, not for boosting an already-adequate immune system. Vitamin D3 has the clearest data, particularly in people who test low. Vitamin C's famous cold-fighting reputation doesn't hold up well for the general population — it may modestly shorten cold duration in some groups, notably people under heavy physical stress, but doesn't prevent colds outright. Vitamin A's immune role is well established biologically, but most of the strong trial evidence comes from deficient populations rather than supplementation on top of a normal diet. Testing before dosing is the more evidence-aligned approach for all three.

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