Background: The vitamin business is a multimillion dollar industry. Aggressive marketing strategies are used to make claims for the health benefits of these products. Observational studies suggest that people who consume vitamin supplements decrease their risks for cancer, cardiovascular disease, and gastrointestinal disease. What is the evidence for these claims, and as a prescribing gastroenterologist, is there a scientific basis for vitamin supplementation?
Methods: A narrative review focusing on randomized controlled trials, where available, plus observational studies obtained from personal files, "on-line" searches, and references in reviewed articles.
Results: From the perspective of a gastroenterologist, there is strong evidence to recommend B12 supplementation in gastric and intestinal disease, as well as pernicious anemia. There exists moderate evidence to support B12 supplements in pancreatic disease. Vitamin D and calcium supplementation are recommended for persons with disorders of malabsorption, cholestasis, and illnesses requiring chronic steroids. Only observational studies suggest a correlation between vitamin D/calcium and decreased colorectal adenoma recurrence. Although folic acid supplementation is beneficial in persons on medications such as methotrexate and sulfasalazine, studies are contradictory with regard to folic acid and colon cancer prevention. Overall, antioxidants have not been proven to decrease the risk for colorectal adenoma, gastric cancer, or esophageal cancer.
Conclusions: Observational studies do not correlate with randomized clinical trials; therefore, few definitive recommendations can be made. Vitamin supplements are appropriate for recognized deficiencies; however, there is a lack of evidence to support their effects in the prevention of chronic disease.