Vitamin D is less a vitamin and more a hormone, and higher levels of this substance are linked with a reduced risk of many conditions including multiple sclerosis, heart disease and several forms of cancer. In some studies, vitamin D has been tested as a treatment, and at least some evidence points to it having value here, including evidence which finds vitamin D can have mood-enhancing and anti-depressant effects .
I came across this relevant report today, which gives an account of a ‘case series’ presented at a recent scientific meeting. It tells of three women suffering from major depression and, at the same time were, were found to be deficient in vitamin D. Vitamin D supplementation improved their vitamin D levels, but even more importantly, appeared to significantly reduce their depression scores too.
These case reports are interesting, I think, and looking for vitamin D deficiency and correcting it appears to be a valid strategy in depression. However, it’s also wroth bearing in mind that while case reports can help stimulate thinking and point the way to future research, they don’t prove or disprove much at all. The usefulness of vitamin D as a treatment for depression can only really be ascertained with any degree of certainty through what are termed ‘randomised controlled trials’ (the sort of trials used to assess the effects of pharmaceutical agents). I think it would be a great service to us for appropriately designed studies to be understaken and the results see the light of day. Certainly, we have a least some evidence  which suggests vitamin D has genuine potential as an antidepressant.
That said, the absence of these trials will not stop me looking for and correcting vitamin D in my patients (whether they are depressed or not).
I realise that burgeoning interest in vitamin D has led to increasing numbers of people wanting to have their vitamin D levels checked. Increasing numbers of doctors seem happy to oblige (at least here in the UK). However, I also know that some doctors refuse their patients which can be frustrating. In the UK, there is a very good (and quite economical) self-testing service here. In the US, self-testing services are available too (see here and here for examples).
1. Jorde R, et al. Effects of vitamin D supplementation on symptoms of depression in overweight and obese subjects: randomized double blind trial. J Intern Med. 2008;264(6):599-609