Vitamin C, also referred to as L-ascorbic acid, is
a water-soluble vitamin that is naturally present in some foods,
fortified in others, and available as a dietary supplement alone or in
multivitamins.1,2 Humans, unlike most animals, cannot synthesize vitamin C de novo and must obtain it as an essential dietary component.1,3
Vitamin C a is required cofactor for the biosynthesis of a number of critical compounds.2,8
It is required for the function of several enzymes involved in the
production of collagen, an essential component of connective tissue.
These enzymes are required for the molecular cross-linking that gives
collagen its elasticity. Vitamin C deficiency renders the polypeptide
unstable and unable to self-assemble into rigid triple helices. Impaired
collagen production can result in poor wound healing and a weakening of
collagenous structures leading to tooth loss, joint pains and bone and
connective tissue pathology and blood vessel fragility. Vitamin C also
serves as a cofactor in the biosynthesis of carnitine, an essential
compound for the transport of activated long chain fatty acids into the
mitochondria. Vitamin C deficiency related reduction in carnitine levels
results in fatigue and lethargy. Vitamin C is an essential cofactor for
the conversion of dopamine to norepinephrine and in the metabolism of
tyrosine and folate and the conversion of cholesterol to bile acids. In
addition, vitamin C in the diet improves the absorption of non-heme
iron, the form of iron present in plant-based foods.9
Profound
and extended vitamin C deficiency leads to scurvy, a condition that is
characterized by blood vessel fragility, connective tissue damage,
fatigue, and, ultimately, death.1-13 Early symptoms can
include weakness, listlessness, as well as shortness of breath and
aching joints, bones and muscles. Myalgias occur because of the reduced
production of carnitine. Oral complications can include gingival
bleeding with minor trauma that proceeds to alveolar bone absorption and
tooth loss. Iron deficiency anemia can also occur due to increased
intestinal bleeding and decreased non-heme iron absorption.10-13 Rheumatologic problems, such as painful hemarthrosis and subperiosteal hemorrhage, may occur.12
Cardiac enlargement may occur because of congestive heart failure
secondary to high-output anemia. Scurvy manifests when vitamin C intake
falls below 10 mg/day for many weeks.10-13 Scurvy is rare in developed countries but can still occur in people with limited food variety and in other high risk groups.
Under
physiological conditions, vitamin C serves as a potent antioxidant and
has been shown to regenerate other antioxidants, particularly vitamin E.2,14-16
The reduced form of the vitamin, ascorbic acid, is a very effective
antioxidant due to its high electron-donating power and ready conversion
back to the active reduced form by glutathione.2 This
antioxidant action plays a role in limiting the damage caused of free
radicals produced by normal metabolic respiration and might serve to
deter the development of certain cancers, cardiovascular disease, and
other diseases.2,14-16 Vitamin C concentration has been shown to be inversely associated with all-cause mortality.17,27 Low plasma vitamin C concentrations are associated with increased blood pressure16,17 and an increased risk of cardiovascular disease9,15,18,21-23 and diabetes.24,25
The
NHANES 2003-2004 revealed that approximately seven percent of the
United States population has deficient serum levels of vitamin C (levels
below 11 umol/L).28 The prevalence of vitamin C deficiency
was markedly higher in smokers relative to nonsmokers, possibly due to
the increased catabolism associated with the oxidative stress of caused
by smoking.2,28 Lower vitamin C levels are seen in the
institutionalized elderly, possibly due to clinical conditions such as
recurrent infections.2 Levels are also lower in low-income compared with the high-income persons.28 Other at-risk groups include persons with gastroinestinal disease or poor dentition.2,12 Cancer patients on chemotherapy who have increased nausea and diarrhea are also at risk, as are patients on hemodialysis.12
Psychiatric disorders including depression, schizophrenia, or anorexia,
also can put patients at risk for reduced intake of vitamin C.12
Alcoholic persons are at risk for scurvy because they may have poorly
balanced diets and because decreases the absorption of vitamin C.12
