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Do low-serum vitamin E levels increase the risk of Alzheimer disease in older people? Evidence from a meta-analysis of case-control studies.
Dong, Y, Chen, X, Liu, Y, Shu, Y, Chen, T, Xu, L, Li, M, Guan, X
International journal of geriatric psychiatry. 2018;(2):e257-e263
Abstract
OBJECTIVE Whether low-serum vitamin E increases the risk of Alzheimer disease (AD) in older people remains inconclusive. This meta-analysis aims to synthesize evidence-based case-control studies to evaluate the association between serum vitamin E and the risk of AD. METHODS Potentially relevant studies were selected through PubMed, Embase, Wanfang, Chongqing VIP, and China National Knowledge Infrastructure databases by using the core terms Vitamin E/alpha-tocopherol and Alzheime's disease/senile dementia/AD in the titles, abstracts, and keywords of the articles. The association between serum vitamin E levels and AD was estimated by using the weighted mean difference (WMD) and 95% confidence interval by adopting a random effects model. Heterogeneity was assessed by using Cochran Q test and I2 statistic. Forest plot was used to present the results graphically from meta-analysis. Publication bias was evaluated by using funnel plots and Egger test. RESULTS We identified 17 studies that met the eligibility criteria. The studies included 2057 subjects with 904 AD patients and 1153 controls. The results indicated that AD patients had a lower concentration of serum vitamin E compared with healthy controls among older people (WMD = -6.811 μmol/L, 95% confidence interval -8.998 to -4.625; Z = -6.105, P < .001). Publication bias was not detected and sensitivity analysis performed by omitting each study, and calculating the pooled WMD again for the remaining studies indicated the results stable. CONCLUSIONS Alzheimer disease is associated with a low concentration of serum vitamin E in older people. However, necessary prospective cohort studies should be conducted to determine the risk of serum vitamin E for AD in the future.
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Link between risk of colorectal cancer and serum vitamin E levels: A meta-analysis of case-control studies.
Dong, Y, Liu, Y, Shu, Y, Chen, X, Hu, J, Zheng, R, Ma, D, Yang, C, Guan, X
Medicine. 2017;(27):e7470
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Abstract
BACKGROUND The effect of low serum vitamin E levels on the risk of colorectal cancer (CRC) remains inconclusive. This meta-analysis aims to synthesize relevant studies to evaluate the association between serum vitamin E and the risk of CRC based on case-control studies. METHODS Potentially relevant studies were selected by searching PubMed, EMBASE, and China National Knowledge Infrastructure databases according to inclusion and exclusion criteria. The association between serum vitamin E levels and CRC was estimated by the weighted mean difference (WMD) and 95% confidence interval (CI) using a random-effects model. Heterogeneity was evaluated using Q test and I statistic. Subgroup analysis was conducted to explore sources of heterogeneity. Sensitivity analysis was performed to reveal stability and reliability. RESULTS A total of 10 papers with 11 studies, including 6431 subjects with 520 CRC patients and 5981 controls, were included in this present meta-analysis. The results indicated that compared with healthy controls, patients with CRC showed lower concentrations of serum vitamin E (WMD = -2.994 μmol/L, 95% CI = -4.395 to -1.593). Ethnicity subgroup analysis indicated that the serum vitamin E levels were lower in European (WMD = -1.82 μmol/L, 95% CI = -3.00 to -0.65), but not in Asian. Control-source subgroup analysis revealed that a significant association was observed in subgroup with hospital-based controls (WMD = -3.43 μmol/L, 95% CI = -6.27 to -0.59), but not in those with population-based controls. Sensitivity analysis suggested no significant difference in the pooled estimates, indicating stable results. CONCLUSIONS CRC is associated with a lower concentration of serum vitamin E. However, necessary prospective cohort studies should be conducted to assess the effect of serum vitamin E on the risk of CRC in the future.