Vitamin supplementation in healthy patients: What does the evidence support?

Since their discovery in the early 1900s as the treatment for life-threatening deficiency syndromes, vitamins have been touted as panaceas for numerous ailments. While observational data have suggested potential correlations between vitamin status and every imaginable disease, randomized controlled trials (RCTs) have generally failed to find benefits from supplementation. Despite this lack of proven efficacy, more than half of older adults reported taking vitamins regularly.¹

While most clinicians consider vitamins to be, at worst, expensive placebos, the potential for harm and dangerous interactions exists. Unlike pharmaceuticals, vitamins are generally unregulated, and the true content of many dietary supplements is often difficult to elucidate. Understanding the physiologic role, foundational evidence, and specific indications for the various vitamins is key to providing the best recommendations to patients.

Vitamins are essential organic nutrients, required in small quantities for normal metabolism. Since they are not synthesized endogenously, they must be ingested via food intake. In the developed world, vitamin deficiency syndromes are rare, thanks to sufficiently balanced diets and availability of fortified foods. The focus of this article will be on vitamin supplementation in healthy patients with well-balanced diets. TABLE E1² lists the 13 recognized vitamins, their recommended dietary allowances, and any known toxicity risks. TABLE 2² outlines elements of the history to consider when evaluating for deficiency. A summary of the most clinically significant evidence for vitamin supplementation follows; a more comprehensive review can be found in TABLE 3.^3-96

B Complex vitamins

Vitamin B1

Vitamers: Thiamine (thiamin)

Physiologic role: Critical in carbohydrate and amino-acid catabolism and energy metabolism

Dietary sources: Whole grains, meat, fish, fortified cereals, and breads

Thiamine serves as an essential cofactor in energy metabolism.² Thiamine deficiency is responsible for beriberi syndrome (rare in the developed world) and Wernicke-Korsakoff syndrome, the latter of which is a relatively common complication of chronic alcohol dependence. Although thiamine’s administration in these conditions can be curative, evidence is lacking to support its use preventively in patients with alcoholism.³ Thiamine has additionally been theorized to play a role in cardiac and cognitive function, but RCT data has not shown consistent patient-oriented benefits.^4,5

The takeaway: Given the lack of evidence, supplementation in the general population is not recommended.

Continue to: Vitamin B2...