The recommended dietary allowance (RDA) is the average daily intake of a nutrient necessary to meet the requirements of a healthy person, as explained by the U.S. National Institutes of Health (NIH). RDAs for vitamin C (ascorbic acid or ascorbate) are set higher than the amount needed to prevent deficiency. For babies, the measurement known as Adequate Intake (AI) is set by the Food and Nutrition Board (FNB) of the Institute of Medicine because RDAs have not been determined for that age group.
The FNB set an AI of vitamin C for babies at 40mg daily from birth to 6 months, and 50mg daily from 7 to 12 months. This is equivalent to the average intake of vitamin C in healthy infants who are breastfed. The FNB considers breast milk an adequate source of vitamin C, and does not recommend feeding infants any form of cow's milk. Cow's milk contains very little ascorbic acid, and heat can destroy this vitamin. Both boys and girls need a minimum of 40mg of vitamin C daily from birth to 6 months, and 50mg daily from 7 to 12 months.
Children and Adults
Boys and girls age 1 to 3 years have an RDA of 15mg of vitamin C daily, according to the NIH. Those 4 to 8 years need 25mg daily, and kids 9 to 13 years old need 45mg daily. Considerations are made by gender starting at age 14, when girls have an RDA of 65mg of vitamin C daily until age 18, and boys an RDA of 75mg during this age range. From 19 onward, women require 75mg of vitamin C per day, although pregnant women have an RDA of 80 to 85mg and breastfeeding women 115 to 120mg. Men 19 and over have a vitamin C RDA of 90mg per day.
People who smoke need 35mg more vitamin C per day than nonsmokers, as noted by the NIH. This is partly because smokers have increased oxidative stress, and ascorbic acid is an antioxidant. Regular exposure to secondhand smoke also calls for higher vitamin C intake, although a specific requirement is not set.
People with certain health conditions or dietary behaviors may not obtain enough vitamin C if consuming only the RDA for their age group. These include elderly, poor, homeless or mentally ill people who eat a limited variety or amount of foods. Individuals who abuse alcohol or other drugs, or who follow diets not providing adequate nutrition, may need vitamin C supplementation. Some medical conditions can reduce vitamin C absorption, such as intestinal malabsorption, AIDS, end-stage kidney disease and certain types of cancer. A study published in the November 2009 issue of "Gastroenterology" noted that some surgical and trauma patients, and those developing septic shock, experience a drastic drop in blood levels of ascorbate. Critically ill patients and burn victims also may need greater vitamin C intake. All these individuals have increased vitamin C requirements due to oxidative stress and wound healing.