CONTEXT: Although vitamin deficiency is encountered infrequently in developed 
countries, inadequate intake of several vitamins is associated with chronic 
disease.
OBJECTIVE: To review the clinically important vitamins with regard to their 
biological effects, food sources, deficiency syndromes, potential for toxicity, 
and relationship to chronic disease.
DATA SOURCES AND STUDY SELECTION: We searched MEDLINE for English-language 
articles about vitamins in relation to chronic diseases and their references 
published from 1966 through January 11, 2002.
DATA EXTRACTION: We reviewed articles jointly for the most clinically important 
information, emphasizing randomized trials where available.
DATA SYNTHESIS: Our review of 9 vitamins showed that elderly people, vegans, 
alcohol-dependent individuals, and patients with malabsorption are at higher 
risk of inadequate intake or absorption of several vitamins. Excessive doses of 
vitamin A during early pregnancy and fat-soluble vitamins taken anytime may 
result in adverse outcomes. Inadequate folate status is associated with neural 
tube defect and some cancers. Folate and vitamins B(6) and B(12) are required 
for homocysteine metabolism and are associated with coronary heart disease risk. 
Vitamin E and lycopene may decrease the risk of prostate cancer. Vitamin D is 
associated with decreased occurrence of fractures when taken with calcium.
CONCLUSIONS: Some groups of patients are at higher risk for vitamin deficiency 
and suboptimal vitamin status. Many physicians may be unaware of common food 
sources of vitamins or unsure which vitamins they should recommend for their 
patients. Vitamin excess is possible with supplementation, particularly for 
fat-soluble vitamins. Inadequate intake of several vitamins has been linked to 
chronic diseases, including coronary heart disease, cancer, and osteoporosis