According to the WHO, most adults need only 45 mg of vitamin C per day, but more recent research has shown this number to be too low. The minimum has been set at 75 mg for women and 90 mg for men in the U.S., and 95 mg for women and 110 mg for men in the E.U.

Moreover, a 2022 study using 110 mg as its starting number recommended adding 10 mg per 10 kg (22 lb) above 60 kg (132 lb) of body weight.^[1]

Any of these numbers are easily attained through the diet, so supplementation of such low doses is usually unnecessary. Higher doses of vitamin C, up to 2,000 mg, are used to support the immune system (for athletes) or reduce the duration of the common cold.

Most studies on vitamin C prescribe one dose per day. The claim that taking 2,000 mg up to five times a day to optimally reduce cold symptoms is not sufficiently tested and requires more evidence.