Check daily vitamin C intake.
Vitamin C is unusually easy to obtain from food — a single orange or a serving of red pepper covers most of an adult day's requirement — so the useful question is rarely whether you reach the target but whether supplements are pushing you toward the 2000 mg tolerable upper intake level. Vegetable servings are credited at 30 mg, a reasonable average across broccoli, peppers, tomatoes and greens, since vitamin C degrades with cooking and storage.
Daily vitamin C total
Total mg = citrus servings x mg per serving + vegetable servings x 30 mg + supplement mg; upper limit share = total / 2000 x 100
These figures are population-average estimates for general planning only and are not medical or dietetic advice. Individual energy and nutrient needs vary widely with body composition, activity, medication and health status. Consult a qualified health professional or registered dietitian before making significant changes to what you eat, and especially if you are pregnant or breastfeeding, are under 18, or have a medical condition or a history of disordered eating.
About 90 mg a day for men and 75 mg for women in US guidance, with an extra 35 mg for smokers because of higher oxidative turnover. EU reference intake is 80 mg. Only around 10 mg a day is needed to prevent scurvy.
Regular supplementation does not reduce how often healthy adults catch colds. Trials show a small reduction in duration, on the order of 8-14 percent, and a clearer effect only in people under heavy physical stress such as marathon runners.
Doses above roughly 2000 mg a day commonly cause diarrhoea, nausea and abdominal cramps, and raise urinary oxalate, which matters for anyone with a history of kidney stones. Absorption efficiency also falls sharply above about 200 mg in a single dose.