Magnesium deficiency and long-term incident dementia among COVID-19 survivors: a propensity score-matched cohort study.

Background: COVID-19 survivors face an elevated risk of long-term cognitive decline, yet potentially modifiable factors that shape post-COVID dementia trajectories remain insufficiently characterized. Low magnesium status has been linked to dementia risk in general populations, but whether low magnesium status is associated with long-term dementia risk among COVID-19 survivors remains unclear. Methods: This propensity score-matched retrospective cohort study used the TriNetX Global Collaborative Network to examine the association between low serum magnesium ( < 1.7 mg/dL on two measurements) and incident dementia among hospitalized COVID-19 survivors aged ≥ 55 years (2020-2023). A 1-year landmark period was imposed to reinforce temporal separation between exposure and outcome. The primary outcome was overall incident dementia over 5 years. Secondary outcomes included Alzheimer's disease, vascular dementia, other dementia types, and mild cognitive impairment. Results: After matching, 58,991 patients with low magnesium and 58,991 controls were included. Magnesium deficiency was associated with a higher risk of overall dementia [2.12% vs. 1.77%; hazard ratio (HR) 1.39, 95% confidence interval (CI) 1.28-1.51; Conclusion: In this observational study, low serum magnesium was associated with increased long-term dementia risk among COVID-19 survivors. Because eligibility required repeated magnesium testing and follow-up healthcare visits were marginally more frequent in the low-magnesium group, selection bias and differential dementia detection cannot be excluded. These hypothesis-generating findings warrant prospective validation.