Purpose: To map and grade all health outcomes associated with magnesium (Mg) intake and supplementation using an umbrella review.Methods: Umbrella review of systematic reviews with meta-analyses of observational studies and randomized controlled trials (RCTs) using placebo/no intervention as control group. We assessed meta-analyses of observational studies based on random-effect summary effect sizes and their p values, 95% prediction intervals, heterogeneity, small-study effects and excess significance. For meta-analyses of RCTs, outcomes with a random-effect p value < 0.005 and a high-GRADE assessment were classified as strong evidence.Results: From 2048 abstracts, 16 meta-analyses and 55 independent outcomes were included (36 in RCTs and 19 in observational studies). In RCTs of Mg versus placebo/no active treatment, 12 over 36 outcomes reported significant results (p < 0.05). A strong evidence for decreased need for hospitalization in pregnancy and for decreased risk of frequency and intensity of migraine relapses in people with migraine was observed using the GRADE assessment. In observational studies, 9/19 outcomes were significant (p < 0.05). However, only one outcome presented highly suggestive evidence (lower incidence of type 2 diabetes in people with higher Mg intake at baseline) and one suggestive (lower incidence of stroke associated with higher Mg intake at baseline).Conclusion: Strong evidence according to the GRADE suggests that Mg supplementation can decrease the risk of hospitalization in pregnant women and reduce the intensity/frequency of migraine. Higher Mg intake is associated with a decreased risk of type 2 diabetes and stroke with highly suggestive and suggestive evidence, respectively, in observational studies.