With thanks to u/FuzzyKittenIsFuzzy and a post in a previous thread, which I think deserves attention.
A total of four trials involving 948 participants were included in the study. In three trials, the intervention group received oral vitamin D supplementation whereas in one parenteral vitamin D was given. Pooled mean effect size for vitamin D supplementation on depressive symptom ratings in major depression was 0.58 (95% confidence interval, 0.45–0.72). The I2 value for heterogeneity was 0 suggesting low heterogeneity among studies. Egger plot intercept indicated minimal publication bias.
Vitamin D supplementation favorably impacted depression ratings in major depression with a moderate effect size. These findings must be considered tentative owing to the limited number of trials available and inherent methodological bias noted in few of them.
That's good. Actually, that's good enough that I was immediately skeptical.
Here are the studies analyzed:
Salient points: this is carried out in dialysis patients.
After 52 weeks, the depressive symptoms were not significantly improved in the test group… versus the control group.
But they did find improvement in vascular depression, for what that's worth. Still, this study's inclusion in the meta-analysis immediately makes me skeptical, because they're pooling a very different population. It doesn't necessarily violate their protocol, but I'm not sure this is good statistical behavior.
Vitamin D Supplementation Affects the Beck Depression Inventory, Insulin Resistance, and Biomarkers of Oxidative Stress in Patients with Major Depressive Disorder: A Randomized, Controlled Clinical Trial.
Results: …A trend toward a greater decrease in the BDI was observed in the vitamin D group than in the placebo group (−8.0 and −3.3, respectively, P = 0.06).
Conclusion: Overall, vitamin D supplementation of patients with MDD for 8 wk had beneficial effects on the BDI…
I don't think the conclusion is justified by the results. It's a small trial (20 people in each arm, of whom 18 in each completed the study), so that's suggestive, but you can't conclude when you didn't reach significance due to underpowered trial. Still, grist for the larger meta-analysis.
The name says it: this is vitamin D supplementation in vitamin D deficiency. I'm not surprised that it helped, and it confirms that vitamin D deficiency can contribute to depression, but not that depression per se can be improved by vitamin supplementation. Again, the inclusion of this study looks to me like something that negatively affects generalizability.
I don't have access to the paper, just the abstract. They say the results are positive without anything more specific. That's encouraging, I guess! I can't really evaluate the study, which is too bad, because this is probably the most real-world useful result.
And two studies were excluded but are important:
The findings do not support a relation between supplementation with 400 IU/day of vitamin D3 along with calcium and depression in older women
The title gives this one away: "In elderly post-menopausal women there was no effect of hormone therapy and calcitriol either individually or in combination with depression."
These are two much larger, negative trials, although they don't neatly map into the criteria. Just like including the first trial (Wang et al.) gives huge boost to number studied, these two would really drag down the results.
Overall, if you drop Wang (unless you're treating dialysis patients), what I think is a reasonable take-home is that it's worth testing for vitamin D deficiency or insufficiency and treating. It's low-risk and potentially beneficial anyway! In non-insufficient patients, however, I don't see data to justify the strong conclusion of the meta-analysis.
I welcome anyone else's thoughts!
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