Vitamin D and cognitive function: The Tromsø Study

Abstract

Background and purpose: There are indications that vitamin D may be important for more than skeletal health, including cognitive function.

Methods: The study was performed in Tromsø, Northern Norway (The Tromsø Study). In a cross-sectional study serum 25-hydroxyvitamin D (25(OH)D) was measured and cognitive function (word recall, digit-symbol coding, finger tapping, Mini Mental State Examination) tested in 4624 subjects; in a prospective study serum 25(OH)D was measured in samples from 1994 and compared to cognitive function tested in 3436 subjects in 2001 and 2044 subjects in 2007; and in a Mendelian randomization study single nucleotide polymorphisms (SNPs) related to vitamin D were evaluated versus cognitive function in 5980 subjects.

Results: In the cross-sectional study all tests were positively associated with serum 25(OH)D levels with ~5% better performance in subjects in the highest versus lowest serum 25(OH)D quartile. This relation was only seen in subjects older than 65 years. After full adjustment for season, age, gender, body mass index, blood pressure, physical activity and education, the relation was only significant for finger tapping. In the prospective study, serum 25(OH)D from 1994 similarly predicted cognitive function 7-13 years later. In the Mendelian randomization study, only one SNP in the VDR gene (Apal, rs7975232) was significantly associated with cognition (word recall and digit-symbol coding).

Conclusions: There is an association between serum 25(OH)D and cognition, but randomized controlled trials are needed to establish causality.

Keywords: Cognition; Mendelian randomization; Polymorphisms; Prospective study; Vitamin D; Vitamin D receptor.