Vitamin D status is associated with executive function a decade later: Data from the Women's Healthy Ageing Project.

Objectives: Vitamin D deficiency has been associated with cognitive decline and dementia in older adults. However, there is a paucity of studies assessing whether this association manifests from midlife. Given the long prodromal stage of dementia, we investigated the association between midlife vitamin D and cognition 10 years later.

Study Design: 252 participants (aged 55-67 years) from the Women's Healthy Ageing Project had baseline (2002) vitamin D and neuropsychological measures assessed. Of these, 170 (aged 65-77 years) had follow-up neuropsychological testing (2012).

Outcome Measures: Serum 25-hydroxyvitamin D (25[OH]D) was measured using an automated chemiluminescence system. The neuropsychological tests used were: Consortium to Establish a Registry for Alzheimer's Disease (CERAD), California Verbal Learning Test Second Edition (CVLT-II), verbal fluency and Trail Making Test-B (TMT-B). Composite scores for verbal episodic memory (CERAD and CVLT-II) and executive function (verbal fluency and TMT-B) were obtained by summating standardized scores for each test.

Results: Analyses were adjusted for age, education and body mass index (BMI). Further adjustment for physical activity, depression, vascular risk factors, supplementation and APOE4-genotype did not materially change the results. At baseline, those with vitamin D>25nmol/L performed better on verbal fluency (β=2.46, 95%CI=0.53,4.40) and TMT-B time (β=-18.23, 95%CI=-32.86,-3.61), with higher executive function (β=1.40, 95%CI=0.44,2.37). These relationships persisted 10 years later for TMT-B (β=-15.38, 95%CI=-30.82,0.07) and executive function (β=1.05, 95%CI=0.14,1.95). There were no associations with tests of verbal episodic memory.

Conclusion: Midlife vitamin D>25nmol/L is associated with improved aspects of executive function in ageing. Findings highlight a potential therapeutic age window where midlife vitamin D repletion could be neuroprotective against cognitive decline.