Homocysteine: A modifiable culprit of cognitive impairment for us to conquer?

Cognitive impairment, including mild cognitive impairment and its progressive deterioration to dementia, results in great hazards to the patient and the surrounding society. While some of the risk factors are unmodifiable, such as age, lower educational attainment, and genetic factors, another proposed one-homocysteine, an amino acid produced in the methylation cycle of protein metabolism is modifiable by cheap and easily accessible B-vitamins treatments in medical practice.

To investigate the relationship between homocysteine and cognitive impairment, elucidate the underlying pathophysiological mechanisms and exploit any potential therapeutic values of homocysteine-lowering treatments in prevention and/or treatment in cognitive decline, we searched on the PUBMED databases surrounding around the physiological homocysteine metabolism, detrimental effects of abnormal homocysteine concentrations on the brain, and review observational and interventional experiments to date estimating the relationship between homocysteine and cognitive impairment with relatively powerful evidence.

Intrinsic and environmental factors help maintain the normal homocysteine concentrations, and pathological homocysteine concentrations exert adverse effects mediated by cellular and vascular pathways. Although many observational studies have suggested a causal link between hyperhomocysteinemia and cognitive impairment, the majority of randomized controlled trials failed to observe marked benefits on cognition by homocysteine-lowering treatments using B-vitamins, partly arising from some design limitations including: not identifying individuals at earlier stages of cognitive impairment who are most likely to benefit, overlooking any latent safety hazards of multiple vitamin supplementation, lack of sensitive and domain-specific cognitive tests, and interference of other underappreciated factors.

More studies are required to better explain the related pathophysiological mechanisms, improve experimental methods, and investigate the preventive or/and therapeutic effects of homocysteine-lowering strategies on cognitive impairment.