This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': 'With ageing, a slight decrease in cognitive impairment is seen due to increase in level of: \nSelect and explain. \nA. Methionine, B. Cysteine, C. Homocysteine, D. Taurine', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Homocysteine and Dementia\n\nHomocysteine is an amino acid that has been shown to have direct and indirect neurotoxic effects in vitro at high concentrations.\nSeveral observational studies have consistently shown cross-sectional association between high levels of serum homocysteine levels and impaired cognitive function (dementia). This association has generally been greater among elderly than among the middle aged.\nCurrent data demonstrate that homocysteine is strongly associated with cognitive dysfunction in ageing. However, it is not yet clear whether this association is causal or whether lowering homocysteine levels improve cognition.\nVitamin B12, folate and homocysteine are closely interlinked and supplementation of vitamin B12 and folate in the diet has been used to reduce homocysteine levels.', 'role': 'assistant'}]