Abstract
Background and objectives: Mental health disorders are the leading cause of ill health and disability in adults, with depression and anxiety being the most prevalent. Emerging evidence indicates roles for specific nutrients—particularly, omega-3 fatty acids, vitamin D, folate, and the metabolically related B vitamins (B12, B6 and riboflavin)—in protecting against depression and anxiety, but the evidence is conflicting. The aim was to conduct a systematic review and meta-analysis investigating the effect of intervention with nutritional factors on mental health outcomes in adults. Methods: Searches were conducted using the following electronic bibliographic databases: MEDLINE, EMBASE and PsycINFO. Inclusion criteria were randomised controlled trials (RCTs) or controlled dietary interventions, participants aged ≥18 years, study duration ≥12 weeks and depression or anxiety outcome measures. The risk of bias and quality of the evidence were assessed using the Cochrane Risk of Bias 2 tool and the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) framework, respectively. Results: A total of 83 studies met the inclusion criteria, of which 73 were included in the meta-analysis. Regarding the role of specific nutrients in depression, RCTs with B vitamins (standardised mean difference, SMD, −1.91 95% CI −3.69, −0.13) and zinc (SMD −0.59 95% CI −0.86, −0.30) indicated significant benefits in reducing depression. Although no overall effect of vitamin D intervention in reducing depression for studies was found, subgroup analysis showed a beneficial effect of 12-week duration (SMD −0.29 95% CI −0.57, −0.01), while no significant effect of omega-3 fatty acid intervention was observed (SMD −0.47 95% CI −0.98, 0.04). RCTs with vitamin D indicated beneficial effects in reducing anxiety (SMD −0.69 95% CI −1.27, −0.11). No significant effect of omega-3 fatty acids on anxiety was shown, while there were insufficient RCTs with B vitamins and zinc in relation to anxiety. Discussion: This preliminary analysis demonstrated a potential role for B vitamins, vitamin D and zinc, but no benefit of intervention with omega-3 fatty acids, on depression. Vitamin D may play a role in reducing anxiety, whereas omega-3 does not. Confirmation of these preliminary findings is required from new RCTs with relevant nutrients.
Author Contributions
Conceptualization, H.M. and C.H.; methodology, H.M. and C.H.; formal analysis, L.M.; performed the statistical analysis, L.M. and S.G.; investigation, L.M., C.H., L.H. and M.C.; data curation, L.M., C.H. and L.H.; writing—original draft preparation, L.M.; writing—review and editing, L.M., C.H., L.H., M.W. and H.M.; supervision, C.H., L.H., M.W. and H.M.; project administration, L.M. All authors have read and agreed to the published version of the manuscript.
Funding
This work was supported by the Department for the Economy (DfE).
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
Not applicable.
Conflicts of Interest
The authors declare no conflict of interest.
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