A study published in the American Journal of Clinical Nutrition reports that in an 18-year follow-up study they found no association between vitamin D and the incidence or dementia or cognitive impairment.
It is known that vitamin D, made from its immediate precursor 25(OH)D, is active in brain regions important for memory and cognition. Dementia is a broad term describing symptoms such as memory disorders, personality changes, and impaired reasoning. Alzheimer’s, a progressive disease that commonly affects elderly individuals, is the most common form of dementia, causing problems with memory, thinking and behaviour. Several observational studies with short follow-up times have suggested that low levels of vitamin D are associated with Alzheimer’s disease, dementia, and cognitive impairment. Observations from longer follow-up studies have yielded conflicting results and left an unclear picture surrounding the association of vitamin D with the incidence of dementia and cognitive impairment.
In an effort to clarify the association and avoid issues associated with observational studies, a novel study published in the American Journal of Clinical Nutrition used a Mendelian randomized approach to investigate the relationship between vitamin D and the risk of dementia in 1182 Swedish men. The mean age of the men at the beginning of the study when baseline measurements were collected was 71 years, and at the end of the study when outcomes were assessed was 82 years. The three baseline vitamin D exposures measured were levels of 25(OH)D in plasma (a component of blood), dietary intake assessed by a 7-day food record and a genetic risk score (GRS) for synthesis of vitamin D. The GRS takes into account the subjects genetic makeup and how that might affect their ability to synthesize (make) vitamin D. The Mini-Mental State Examination, a commonly used 30-point questionnaire, was used to assess baseline and outcome dementia, and cognitive impairment at the beginning and end of the study.
The researchers conclude that over a total of 18 years of follow-up, no associations were shown between vitamin D and Alzheimer’s disease, dementia or cognitive decline. This study does not include women or take into account information on sun exposure, a key source of vitamin D. Another limitation of the study is that measures of plasma 25(OH)D and dietary vitamin D were not measured repeatedly, only as baseline at the beginning of the study.
Written By: Katherine M. Evely, MS