Reductive stress, characterised by an increased NADH:NAD+ ratio, may be as common and as important a consequence of redox imbalance as oxidative stress. It may also be an important predisposing cause of the generation of reactive oxygen species. Considerable experimental and indirect clinical evidence suggests that protection against reductive stress depends on biomolecules with electrophilic methyl groups (EMG) such as S-adenosylmethionine, betaine, carnitine and phosphatidylcholine. Pathological processes leading to reductive stress and their relief by such protective agents is reviewed and the proposed molecular mechanism is outlined. These and other EMG-containing biomolecules are part of the daily diet and may represent an important control system for redox balance.
