American Academy of Neurology
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July 13, 2026
David J. Llewellyn, PhD; Iain A. Lang, PhD; Kenneth M. Langa, MD, PhD; Graciela Muniz-Terrera, PhD; Caroline L. Phillips, MS; Antonio Cherubini, MD; Luigi Ferrucci, MD, PhD; David Melzer, PhD
To our knowledge, no prospective study has examined the association between vitamin D and cognitive decline or dementia. We determined whether low levels of serum 25-hydroxyvitamin D (25[OH]D) were associated with an increased risk of substantial cognitive decline in the InCHIANTI population–based study conducted in Italy be- tween 1998 and 2006 with follow-up assessments every 3 years. A total of 858 adults 65 years or older completed interviews, cognitive assessments, and medical examinations and provided blood samples. Cognitive decline was assessed using the Mini-Mental State Examination (MMSE), and substantial decline was defined as 3 or more points. The Trail-Making Tests A and B were also used, and substantial decline was defined as the worst 10% of the distribution of decline or as discontinued testing.