Table 2.

Meta-regression coefficients and standard error on the relation between study characteristics and effect-size estimates, separately for the different indicators that are in use to operationalise the hypothesis of Mg²⁺ involvement in mood disorders

	Dietary Mg2+ a k = 12 n = 21 927	Fluid Mg2+ b k = 62 n = 4433	Fluid Mg2+ c k = 11 n = 827	Mg2+ treatment k = 11 n = 714
Year	−0.007 (0.055)	0.008 (0.009)	0.005 (0.008)	0.015 (0.039)
N	0.0001 (0.001)*	−0.005 (0.001)**	0.001 (0.001)	0.002 (0.003)
Age of the sample	−0.009 (0.008)	−0.001 (0.010)	0.001 (0.006)	0.004 (0.014)
% Female	−0.003 (0.007)	−0.002 (0.004)	−0.002 (0.003)	0.016 (0.013)
Methodological quality	−0.046 (0.165)	0.001 (0.061)	−0.014 (0.073)	−0.377 (0.695)
Treatment weeks	N.A.	N.A.	N.A.	−0.082 (0.073)

N.A., not applicable.

In order to aid with interpretation, we include a synopsis. Sample size was positively associated with the effect-size estimates in dietary studies; this indicates that smaller samples on average yielded stronger associations between dietary Mg²⁺ and depression prevalence (the strength of this association in terms of Spearman's rho (ρ) was 0.61). Sample size was negatively associated with the effect-size estimates in studies investigating differences in Mg²⁺ in bodily fluids between patients and healthy control subjects. This means that smaller samples on average yielded larger differences (the strength of this association was ρ = −0.42).

^a.Results are presented for cross-sectional data only. There were only two prospective studies available and hence separate meta-regression analyses were not possible. Results from the analyses were no different when the prospective studies were pooled with the cross-sectional.

^b.Mean differences in bodily fluid Mg²⁺ levels between patients with a mood disorder and healthy control subjects.

^c.Continuous differences in bodily fluid Mg2⁺ levels as a function of mood disorder symptom severity.

^*P < 0.05; **P < 0.01.