Vitamin C Intakes and Status
According to the 2001–2002 National Health and Nutrition Examination Survey (NHANES), mean intakes of vitamin C are 105.2 mg/day for adult males and 83.6 mg/day for adult females, meeting the currently established RDA for most nonsmoking adults. Mean intakes for children and adolescents aged 1-18 years range from 75.6 mg/day to 100 mg/day, also meeting the RDA for these age groups. Although the 2001–2002 NHANES analysis did not include data for breastfed infants and toddlers, breastmilk is considered an adequate source of vitamin C. Use of vitamin C-containing supplements is also relatively common, adding to the total vitamin C intake from food and beverages. NHANES data from 1999–2000 indicate that approximately 35% of adults take multivitamin supplements (which typically contain vitamin C) and 12% take a separate vitamin C supplement. According to 1999–2002 NHANES data, approximately 29% of children take some form of dietary supplement that contains vitamin C.
Vitamin C status is typically assessed by measuring plasma vitamin C levels. Other measures, such as leukocyte vitamin C concentration, could be more accurate indicators of tissue vitamin C levels, but they are more difficult to assess and the results are not always reliable.
Vitamin C Deficiency
Acute vitamin C deficiency leads to scurvy. The timeline for the development of scurvy varies, depending on vitamin C body stores, but signs can appear within 1 month of little or no vitamin C intake (below 10 mg/day). Initial symptoms can include fatigue (probably the result of impaired carnitine biosynthesis), malaise, and inflammation of the gums. As vitamin C deficiency progresses, collagen synthesis becomes impaired and connective tissues become weakened, causing petechiae, ecchymoses, purpura, joint pain, poor wound healing, hyperkeratosis, and corkscrew hairs. Additional signs of scurvy include depression as well as swollen, bleeding gums and loosening or loss of teeth due to tissue and capillary fragility. Iron deficiency anemia can also occur due to increased bleeding and decreased nonheme iron absorption secondary to low vitamin C intake. In children, bone disease can be present. Left untreated, scurvy is fatal.
Until the end of the 18th century, many sailors who ventured on long ocean voyages, with little or no vitamin C intake, contracted or died from scurvy. During the mid-1700s, Sir James Lind, a British Navy surgeon, conducted experiments and determined that eating citrus fruits or juices could cure scurvy, although scientists did not prove that ascorbic acid was the active component until 1932.
Today, vitamin C deficiency and scurvy are rare in developed countries. Overt deficiency symptoms occur only if vitamin C intake falls below approximately 10 mg/day for many weeks. Vitamin C deficiency is uncommon in developed countries but can still occur in people with limited food variety.
Groups at Risk of Vitamin C Inadequacy
Vitamin C inadequacy can occur with intakes that fall below the RDA but are above the amount required to prevent overt deficiency (approximately 10 mg/day). The following groups are more likely than others to be at risk of obtaining insufficient amounts of vitamin C.
Smokers and passive “smokers”
Studies consistently show that smokers have lower plasma and leukocyte vitamin C levels than nonsmokers, due in part to increased oxidative stress. For this reason, the IOM concluded that smokers need 35 mg more vitamin C per day than nonsmokers. Exposure to secondhand smoke also decreases vitamin C levels. Although the IOM was unable to establish a specific vitamin C requirement for nonsmokers who are regularly exposed to secondhand smoke, these individuals should ensure that they meet the RDA for vitamin C.
Infants fed evaporated or boiled milk
Most infants in developed countries are fed breastmilk and/or infant formula, both of which supply adequate amounts of vitamin C. For many reasons, feeding infants evaporated or boiled cow’s milk is not recommended. This practice can cause vitamin C deficiency because cow’s milk naturally has very little vitamin C and heat can destroy vitamin C.
Individuals with limited food variety
Although fruits and vegetables are the best sources of vitamin C, many other foods have small amounts of this nutrient. Thus, through a varied diet, most people should be able to meet the vitamin C RDA or at least obtain enough to prevent scurvy. People who have limited food variety—including some elderly, indigent individuals who prepare their own food; people who abuse alcohol or drugs; food faddists; people with mental illness; and, occasionally, children—might not obtain sufficient vitamin C.
People with malabsorption and certain chronic diseases
Some medical conditions can reduce the absorption of vitamin C and/or increase the amount needed by the body. People with severe intestinal malabsorption or cachexia and some cancer patients might be at increased risk of vitamin C inadequacy. Low vitamin C concentrations can also occur in patients with end-stage renal disease on chronic hemodialysis.