A study by researchers at the University of York and Hull York Medical School has confirmed a link between depression and low levels of folate, a vitamin which comes from vegetables.
Dr Gilbody said: "Our study is unique in that for the first time all the relevant evidence in this controversial area has been brought together. Although the research does not prove that low folate causes depression, we can now be sure that the two are linked. Interestingly, there is also some trial evidence that suggests folic acid supplements can benefit people with depression. We recommend that large trials should be carried out to further test this suggestion."