A study involving 382 older adults (average age 75) followed for around five years, has found that those who don’t get enough vitamin D may experience cognitive decline at a much faster rate than people who have adequate vitamin D.
Participants included 17.5% with dementia at the beginning of the study, 32.7% with MCI, and 49.5% cognitively healthy.
Those with dementia had lower levels of vitamin D than the other two groups.
While some people with low vitamin D didn’t show any cognitive decline and some with adequate vitamin D declined quickly, people with low vitamin D on average declined two to three times as fast as those with adequate vitamin D, in two crucial cognitive domains: episodic memory and executive function. Semantic memory and visuospatial ability were not significantly affected.
Factors such as age, gender, education, BMI, season of blood draw, vascular risk, and presence of the 'Alzheimer's gene', ApoE4, were controlled for.
Unlike previous studies of vitamin D and dementia, the participants were racially and ethnically diverse and included whites (41%), African Americans (30%), and Hispanics (25%). Nearly two-thirds (61%) had low vitamin D levels in their blood, including 54% of the whites and 70% of the African-Americans and Hispanics.
Vitamin D is primarily obtained through sun exposure. Accordingly, people with darker skin are more likely to have low levels of vitamin D because melanin blocks ultra-violet rays.
It remains to be seen whether Vitamin D supplements could slow cognitive decline.
 . VItamin d status and rates of cognitive decline in a multiethnic cohort of older adults. JAMA Neurology [Internet]. 2015 . Available from: http://dx.doi.org/10.1001/jamaneurol.2015.2115