The RDA for vitamins may be used as goals for each person. How much of each vitamin you need depends on your age and gender. Other factors, such as pregnancy and illnesses, are also important. In 2000, the National Academy of Sciences established the following Adequate Intake levels for vitamin C:
- 0 – 6 months: 40* milligrams/day (mg/day)
- 7 – 12 months: 50* mg/day
*Adequate Intake (AI)
- 1 – 3 years: 15 mg/day
- 4 – 8 years: 25 mg/day
- 9 – 13 years: 45 mg/day
- Girls 14 – 18 years: 65 mg/day
- Boys 14 – 18 years: 75 mg/day
- Men age 19 and older: 90 mg/day
- Women age 19 year and older: 75 mg/day
Smokers or those who are around secondhand smoke at any age should increase their daily amount of vitamin C by 35 mg.
Women who are pregnant or breast-feeding and those who smoke need higher amounts of vitamin C.
Older adults (65 years and older)
Although it is not yet known with certainty whether older adults have higher requirements for vitamin C than younger people, some older populations have been found to have vitamin C intakes considerably below the RDA of 75 and 90 mg/day for women and men, respectively. A vitamin C intake of at least 400 mg daily may be particularly important for older adults who are at higher risk for chronic diseases. In addition, a meta-analysis of 36 publications examining the relationship between vitamin C intake and plasma concentrations of vitamin C concluded that older adults (age 60-96 years) have considerably lower plasma levels of vitamin C following a certain intake of vitamin C compared with younger individuals (age 15-65 years) suggesting that older adults may have higher vitamin C requirements. Studies conducted at the National Institutes of Health indicated that plasma and circulating cells in healthy, young subjects attain near-maximal concentrations of vitamin C at a dose of about 400 mg/day—a dose much higher than the current RDA.
Studies show that a vitamin C intake of at least 400 mg daily is particularly important for older adults who are at higher risk for chronic diseases caused, in part, by oxidative damage, such as heart disease, stroke, certain cancers, and cataract.