Dr. David J. Llewellyn and colleagues from all over the world recently conducted the first large longitudinal 6-year study on vitamin D and dementia. They studied 858 older adults, seeing if low 25(OH)D levels at baseline predicted the onset or worsening of dementia.
Llewellyn DJ, Lang IA, Langa KM, Muniz-Terrera G, Phillips CL, Cherubini A, Ferrucci L, Melzer D. Vitamin D and risk of cognitive decline in elderly persons. Arch Intern Med. 2010 Jul 12;170(13):1135-41.