Malic Acid

Malic acid is a four-carbon dicarboxylic acid with the formula C4H6O5, one of the simple organic acids produced by all living organisms. It occurs in two enantiomeric forms, L-malic and D-malic acid, but only the L-form is made and used biologically; the synthetic material produced industrially is generally a racemic mixture of the two. The compound is the predominant acid in apples and is also abundant in grapes, cherries, and many other fruits, giving them much of their sourness, and its name derives from the Latin word for apple. Industrially it is manufactured on a large scale, historically by the hydration of maleic or fumaric acid.

In metabolism, malate is a key intermediate of the citric acid cycle, the central pathway of aerobic energy production, and it also takes part in processes such as the malate-aspartate shuttle that moves reducing equivalents into mitochondria and, in many plants, in carbon fixation and the control of leaf pores. As a food additive, malic acid carries the European designation E296 and is permitted as an acidulant in numerous countries, where it sharpens tartness in soft drinks, confectionery, and other products and is often paired with or substituted for citric acid.

Interest in malic acid as a supplement has centered partly on muscle energy metabolism, on the rationale that supporting the citric acid cycle might ease muscle pain and fatigue. This idea was tested in a small randomized, double-blind, placebo-controlled crossover pilot study of a proprietary malic acid and magnesium tablet in people with fibromyalgia; the blinded, fixed low-dose phase showed no clear benefit, although an open-label phase using higher doses over a longer period reported reductions in pain and tenderness ^[1]. Later evidence reviews of chronic musculoskeletal pain classified malic acid combined with magnesium among the treatments found not to be effective for fibromyalgia, so this supplement use rests on weak and inconsistent data ^[2].

Malic acid has also been studied topically for dry mouth, or xerostomia. Because it can stimulate saliva flow, it has been formulated into sprays intended to relieve mouth dryness; a systematic review of saliva substitutes and stimulants found that a one percent malic acid topical spray increased both resting and stimulated salivary flow and made patients several times more likely to report improvement than placebo, although the authors rated the overall quality of evidence as low ^[3]. Reviews of xerostomia treatment list malic acid among the agents used to ease symptoms alongside saliva substitutes and other stimulants ^[4]. A recognized caution with acidic saliva stimulants is their potential to erode dental enamel, which is why such products are formulated and used with care.

Generally very safe; high doses can cause GI upset or a laxative effect and its acidity may bother sensitive stomachs. It is widely used as a food additive with a good safety record. No serious interactions are established.