Vitamin C (Ascorbic Acid)

Vitamin C scores 7.5–8.0/10 because the floor is so high and the downside so small: it is essential, decisively effective for deficiency, very safe, and nearly free, with modest real bonuses for blood pressure, glycemia, iron absorption, and cold duration. The practical verdict is to treat it as a cheap nutritional insurance policy rather than a hero supplement. It belongs in the Strong recommend tier not because it transforms healthy people, but because ensuring adequacy is genuinely valuable and the risk of doing so is almost nil. The people who should skip megadoses are healthy, well-fed adults chasing grams or IV drips for benefits the evidence does not support.

✅ Best for: People with low dietary fruit and vegetable intake, who are the clearest beneficiaries of correction. Smokers and heavy drinkers, who have measurably higher requirements. Athletes and others under heavy physical stress, where Hemila 2013 showed regular vitamin C halved cold incidence. Hypertensive adults wanting a cheap adjunct for the modest blood pressure effect from Juraschek 2012. People with type 2 diabetes, where the glycemic signal concentrates at higher doses. Vegetarians and the iron-deficient, who benefit from co-taking it with plant-based iron. The elderly, malnourished, and post-surgical, where adequate vitamin C supports wound healing.

❌ Avoid if: You have a kidney-stone history, chronic kidney disease, or oxalate-stone tendency, since supplemental doses at or above 1000 mg/day roughly doubled stone risk in men. You have hemochromatosis or another iron-overload condition, because vitamin C increases iron absorption. You have G6PD deficiency, where very high doses can trigger hemolysis. You expect grams to deliver dramatic benefits in an already-replete body, or you are considering intravenous vitamin C for cancer or sepsis on the strength of marketing, since the Fowler 2019 sepsis trial and the cancer evidence do not support those frames.