Cholinesterase inhibitors and add-on nutritional supplements in Alzheimer's disease: a systematic review of randomized controlled trials.

To date, single drug and nutrient-based interventions have failed to show a clinically relevant effect on Alzheimer's disease (AD). Multidomain interventions may alleviate symptoms and alter the disease course in a synergistic manner. This systematic review examines the effect of adding nutritional supplementation to cholinesterase inhibitors. A systematic PubMed and Cochrane search resulted in nine high quality studies. The studies had low to moderate risk of bias and focused on oxidative stress, homocysteine levels, membrane fluidity, inflammation and acetylcholine levels. Only the use of vitamin E supplements could reduce the rate of functional decline when combined with cholinesterase inhibitors in one study, whereas cognition was not affected in both this and other studies. None of the other nutritional supplements showed convincing evidence of a beneficial effect when combined with cholinesterase inhibitors. This shows that cognitive and functional improvement is difficult to achieve in patients with AD, despite epidemiological data and evidence of biological effects of nutritional supplements. Addressing one disease pathway in addition to cholinesterase inhibitor therapy is probably insufficient to alter the course of the disease. Personalized, multifactorial interventions may be more successful in improving cognition and daily functioning.