Plasma homocysteine, folate and vitamin B12 levels in Parkinson's disease in China: A meta-analysis

Epidemiological studies evaluating the associations of plasma homocysteine (Hcy), folate and vitamin B12 levels with Parkinson's disease (PD) in China have produced inconsistent results. Therefore, we conducted a meta-analysis to summarize the relationships. PubMed, Cochrane Library, Elsevier Science Direct, Springer, CNKI (China National Knowledge Infrastructure), and Wanfang (Chinese) databases were searched for eligible studies from January 2000 to November 2018. The pooled standardized mean difference (SMD), Fisher's Z and corresponding 95% confidence interval (95% CI) were calculated with fix-effects or random-effects model. In total, 26 case-control studies and 1 cross-sectional study were included in this meta-analysis. The results showed that: (1) PD patients had a higher Hcy level than the control individuals (P < 0.05). After stratification subgroup, significant differences of plasma Hcy level between PD patients and controls were found in subgroup with sample size < 100, sample size 100, as well as in the subgroup analysis by levodopa therapy. (2) Both plasma folate and vitamin B12 levels were lower in the PD patients compared with the control group (P < 0.05). (3) Plasma Hcy level was negatively correlated with plasma levels of folate and vitamin B12 in PD patients (P < 0.05). (4) The relevant influential factors of plasma Hcy level in PD patients were clinical types, Hoehn & Yahr stage, cognitive impairment, or levodopa therapy (P < 0.05). In conclusion, PD patients had a higher Hcy level in China. Multiple factors were associated with Hcy levels of Chinese PD patients.