Low Vitamin D Levels and Risk of Incident Delirium in 351,000 Older UK Biobank Participants

Abstract

BACKGROUND/OBJECTIVES Delirium is common in older adults, especially following hospitalization. Because low vitamin D levels may be associated with increased delirium risk, we aimed to determine the prognostic value of blood vitamin D levels, extending our previous genetic analyses of this relationship.

DESIGN Prospective cohort analysis.

SETTING Community‐based cohort study of adults from 22 cities across the United Kingdom (the UK Biobank).

PARTICIPANTS Adults aged 60 and older by the end of follow‐up in the linked hospital inpatient admissions data, up to 14 years after baseline (n = 351,320).

MEASUREMENTS At baseline, serum vitamin D (25‐OH‐D) levels were measured. We used time‐to‐event models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between vitamin D deficiency and incident hospital‐diagnosed delirium, adjusted for age, sex, assessment month, assessment center, and ethnicity. We performed Mendelian randomization genetic analysis in European participants to further investigate vitamin D and delirium risk.

RESULTS A total of 3,634 (1.03%) participants had at least one incident hospital‐diagnosed delirium episode. Vitamin D deficiency (<25 nmol/L) predicted a large incidence in delirium (HR = 2.49; 95% CI = 2.24–2.76; P = 3*10−68, compared with >50 nmol/L). Increased risk was not limited to the deficient group: insufficient levels (25–50 nmol/L) were also at increased risk (HR = 1.38; 95% CI = 1.28–1.49; P = 4*10−18). The association was independent of calcium levels, hospital‐diagnosed fractures, dementia, and other relevant cofactors. In genetic analysis, participants carrying more vitamin D–increasing variants had a reduced likelihood of incident delirium diagnosis (HR = .80 per standard deviation increase in genetically instrumented vitamin D: .73–.87; P = 2*10−7).

CONCLUSION Progressively lower vitamin D levels predicted increased risks of incident hospital‐diagnosed delirium, and genetic evidence supports a shared causal pathway. Because low vitamin D levels are simple to detect and inexpensive and safe to correct, an intervention trial to confirm these results is urgently needed.