nutrients Article
Associations between Folate and Vitamin B12 Levels and Inflammatory Bowel Disease: A Meta-Analysis Yun Pan 1 , Ya Liu 1 , Haizhuo Guo 2 , Majid Sakhi Jabir 3 , Xuanchen Liu 1 , Weiwei Cui 1, * and Dong Li 4,5, * 1
2 3 4 5
*
Department of Nutrition and Food Hygiene, School of Public Health, Jilin University, 1163 Xinmin Avenue, Changchun 130021, China;
[email protected] (Y.P.);
[email protected] (Y.L.);
[email protected] (X.L.) Department of Radiology, The Second Part of the First Hospital, Jilin University, Changchun 130031, China;
[email protected] Department of Biotechnology, University of Technology, Baghdad 00964, Iraq;
[email protected] Department of Immunology, College of Basic Medical Sciences, Jilin University, 126 Xinmin Avenue, Changchun 130021, China Department of Hepatology, The First Hospital, Jilin University, Changchun 130021, China Correspondence:
[email protected] (W.C.);
[email protected] (D.L.); Tel.: +86-431-8561-9455 (W.C.); +86-431-8561-9476 (D.L.)
Received: 3 February 2017; Accepted: 12 April 2017; Published: 13 April 2017
Abstract: Background: Inflammatory bowel disease (IBD) patients may be at risk of vitamin B12 and folate insufficiencies, as these micronutrients are absorbed in the small intestine, which is affected by IBD. However, a consensus has not been reached on the association between IBD and serum folate and vitamin B12 concentrations. Methods: In this study, a comprehensive search of multiple databases was performed to identify studies focused on the association between IBD and serum folate and vitamin B12 concentrations. Studies that compared serum folate and vitamin B12 concentrations between IBD and control patients were selected for inclusion in the meta-analysis. Results: The main outcome was the mean difference in serum folate and vitamin B12 concentrations between IBD and control patients. Our findings indicated that the average serum folate concentration in IBD patients was significantly lower than that in control patients, whereas the mean serum vitamin B12 concentration did not differ between IBD patients and controls. In addition, the average serum folate concentration in patients with ulcerative colitis (UC) but not Crohn’s disease (CD) was significantly lower than that in controls. This meta-analysis identified a significant relationship between low serum folate concentration and IBD. Conclusions: Our findings suggest IBD may be linked with folate deficiency, although the results do not indicate causation. Thus, providing supplements of folate and vitamin B12 to IBD patients may improve their nutritional status and prevent other diseases. Keywords: folate; vitamin B12; inflammatory bowel disease; meta-analysis; nutrition
1. Introduction Inflammatory bowel disease (IBD) is characterized by chronic and typically recurrent intestinal inflammation, and it includes Crohn’s disease (CD) and ulcerative colitis (UC). Although the exact aetiology and pathogenesis of IBD is still largely unknown, it is considered to be related to individual immunity, an inherited predisposition, environmental factors and the interactions between the mucosal immune system and intestinal antigenic material (e.g., commensal bacteria) [1]. Abnormal immune responses are believed to be the direct cause of intestinal damage [2]. IBD can lead to many clinical symptoms, including impaired nutrient absorption, which can influence the absorption of folate and vitamin B12. Furthermore, many studies have indicated that serum folate and vitamin B12
Nutrients 2017, 9, 382; doi:10.3390/nu9040382
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concentrations influence the development of IBD. Folate is involved in the methylation of DNA and may produce epigenetic changes that affect the interaction between the gut microbiota and systemic immune responses [3]. The gut microbiota [4] and epigenetic changes [5] may be involved in the pathogenesis of IBD. Vitamin B12 acts as a coenzyme in various biochemical reactions, including DNA synthesis and folate metabolism [6]. Deficiencies in vitamin B12 and folate can lead to macrocytic anaemia, hyperhomocysteinemia, and neurologic and psychiatric disorders [7–9]. Compared with healthy subjects, IBD patients are at increased risk of hyperhomocysteinemia [10], and folic acid and vitamin B12 may play pivotal roles in homocysteine metabolic reactions [11]. Moreover, folate and vitamin B12 deficiencies may cause increased homocysteine levels, a risk factor for thrombosis [8,12–14]. Many studies have reported that serum folic and vitamin B12 concentrations differ between IBD patients and healthy individuals. However, the results are not consistent, and differences have been observed between patients with CD and UC. Whether serum folic acid and vitamin B12 concentrations are lower in IBD patients than in non-IBD patients is still largely unknown. Thus, a more comprehensive evaluation of the association between IBD and serum folic acid and vitamin B12 concentrations is needed. In this study, we conducted a meta-analysis to analyse the relationships between the serum concentrations of folic acid and vitamin B12 in IBD patients and healthy controls to provide additional insights into treating and rehabilitating IBD and maintaining a healthy nutritional status. 2. Materials and Methods 2.1. Sources and Methods of Data Retrieval We performed a comprehensive literature search that included studies from 1970 to December 2016; the electronic databases included PubMed, Medline, Web of Science, and Google Scholar. The searches were conducted to identify all published studies that reported data on the mean differences and standard deviations of serum folate and vitamin B12 concentrations in IBD patients and healthy controls. The following terms were used for the literature search: folic acid, vitamin B9, vitamin M, folvite, folate, vitamin B12, cyanocobalamin, cobalamins, inflammatory bowel disease, Crohn’s disease, ulcerative colitis. The term ‘OR’ was used as the set operator to combine different sets of results. The serum concentrations of folate and vitamin B12 and IBD were determined and used in a meta-analysis to understand how serum folate and vitamin B12 concentrations differ in IBD patients relative to healthy controls. Age, location, detection methods and other confounding factors were also considered. 2.2. Inclusion Criteria The articles that were included in this meta-analysis matched the following five criteria: (1) inflammatory bowel disease patients were clinically diagnosed; (2) studies included a case group and a control group; (3) the folate and vitamin B12 values were presented as the mean ± standard deviation (SD); and (4) the patients and controls had not previously received folate and vitamin B12 supplementation; and (5) we excluded studies that did not provide initial data, animal studies, in vitro studies, reviews and conference papers. Three investigators independently reviewed and extracted all of the potentially eligible studies and discussed the inconsistencies until a consensus was reached (Figure 1). Additionally, the Newcastle-Ottawa Scale was used for assessing the quality of studies included in this meta-analysis (Table 1). 2.3. Data Abstraction We reviewed all of the relevant studies and extracted the following data: (1) lead author, publication year, sample size, mean age of the patients and controls, and gender of the patients and controls; (2) serum folate and vitamin B12 concentrations of the patients and controls; (3) folate
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andvitamin B12 detection methods; and (4) the diagnosis of the patients and the number of patients and vitamin B12 detection methods; and (4) the diagnosis of the patients and the number of patients andcontrols. controls.
Figure 1. Flow diagram of the literature search.
Figure 1. Flow diagram of the literature search.
2.4. Statistical Analysis
2.4. Statistical Analysis
All statistical analysis was conducted using the statistical software Stata (version 12.0, StataCorp LLC, Station, TX, USA). The mean difference, standard deviation and standard error of the All College statistical analysis was conducted using the statistical software Stata (version 12.0, StataCorp serum folate and vitamin B12 concentrations in the IBD and control group were used for the meta‐ LLC, College Station, TX, USA). The mean difference, standard deviation and standard error of analysis. Units that were not unified were transformed into unified units. We combined the the the serum folate and vitamin B12 concentrations in the IBD and control group were used for standardized mean difference (SMD) for studies that reported mean and standard deviation values for meta-analysis. Units that were not unified were transformed into unified units. We combined the serum folate and vitamin B12 concentrations in IBD patients and controls. An inverse variance weighted standardized mean difference (SMD) for studies that reported mean and standard deviation values random effect model was used to determine the SMD and 95% confidence intervals (CIs) and measure for serum folate and vitamin B12 concentrations in IBD patients and controls. An inverse variance the different concentrations of folate and vitamin B12 in the patients and controls, and the results were weighted random effect model was used to determine the SMD and 95% confidence intervals (CIs) and used to evaluate the differences in serum concentrations of folate and vitamin B12 between the IBD measure the different concentrations of folate and vitamin B12 in the patients and controls, and the patients and normal controls. In order to avoid double counting, both controls in two studies that results were used to evaluate the differences in serum concentrations of folate and vitamin B12 between included both UC and CD patients [15,16] were split approximately evenly into 2 control groups with thethe means and standard deviations left unchanged before entered into the meta‐analysis [17,18]. IBD patients and normal controls. In order to avoid double counting, both controls in two studies that included both UC and Q CDstatistic patients [15,16] splitto approximately evenlyheterogeneity into 2 controlin groups We used Cochran’s and the I2were statistic assess the statistical the with the means and standard deviations left unchanged before entered into the meta-analysis [17,18]. meta‐analysis [19]. If the data were homogeneous (p > 0.05), a fixed effect model meta‐analysis was 2 statistic to assess the statistical heterogeneity in the We used Cochran’s statistic and the I(p performed; if the data Q were heterogeneous ≤ 0.05), a random effects model meta‐analysis was 2 value was meta-analysis [19]. If the data were homogeneous (p > 0.05), a fixed effect model meta-analysis performed. Heterogeneity was considered significant at p
