Association of Plasma Homocysteine, Vitamin B12 and Folate Levels with Cognitive Function in Parkinson's Disease: A Meta-analysis

Hyperhomocysteinemia has been associated with cognitive disorders such as mild cognitive impairment, Alzheimer's disease and vascular dementia. Previous studies showed that levodopa-treated Parkinson's disease (PD) patients were likely to have elevated homocysteine levels. In addition, epidemiological evidence found that cognitive impairment presented in the vast majority of PD patients. However, what role homocysteine played in cognitive function of PD patients remained debated. Therefore, we conducted this meta-analysis to investigate the possible correlations among cognitive function, homocysteine, folate and vitamin B12 levels in PD patients. A structured literature search was carried out on Pubmed, Springer, EMbase, Cochrane library, CNKI, VP and Wanfang database up to April 2016 using strict inclusion criteria. Data on demographic information, levodopa equivalent dosage, homocysteine, folate and vitamin B12 levels and Mini Mental Scale Examination scores were collected and pooled. The mean difference (MD) with 95% confidence intervals (CIs) was used as the effect size. Of 75 articles identified, 15 were eligible for inclusion. The results suggested that PD patients with cognitive dysfunction were likely to have higher homocysteine levels(MD=5.05, 95%CI [4.03, 6.07]), lower folate(MD=-0.21, 95%CI [-0.34, -0.08]) and vitamin B12 levels(MD=-47.58, 95%CI [-72.07, -23.09]). We again verified a close relationship between hyperhomocysteinemia and PD (MD=5.67, 95%CI [4.40, 6.94]). We concluded that hyperhomocysteinemia was related to cognitive impairment of PD patients, and further studies should focus on the intervention to lower homocysteine level, hopefully to provide useful advice for clinical practice.