Be careful - many studies in the Vitamin D meta-analysis *enrolled patients already taking antidepressants.* [1] Reporting effect sizes without specifying "on which population?" is misleading.
(As an aside, Cohen would be the person not to tell you to assign qualitative values to effect sizes. They are as arbitrary as any other threshold used by working statisticians.)
EDIT – that is, please don't draw the conclusion that you can substitute supplements for antidepressants. The meta-analyses don't seem designed to examine that hypothesis, and I doubt anyone would ever participate in a such a trial. In general (and as a working biostatistician), I would be very, very, very cautious applying estimates of average effect to myself, you, or any other individual person in a field as murky as psychiatry. That's why even the stingiest American health insurance plans still have an incredibly large range of antidepressants in their formularies.
(As an aside, Cohen would be the person not to tell you to assign qualitative values to effect sizes. They are as arbitrary as any other threshold used by working statisticians.)
[1] https://www.cambridge.org/core/journals/psychological-medici...
EDIT – that is, please don't draw the conclusion that you can substitute supplements for antidepressants. The meta-analyses don't seem designed to examine that hypothesis, and I doubt anyone would ever participate in a such a trial. In general (and as a working biostatistician), I would be very, very, very cautious applying estimates of average effect to myself, you, or any other individual person in a field as murky as psychiatry. That's why even the stingiest American health insurance plans still have an incredibly large range of antidepressants in their formularies.