New research found that severe vitamin D deficiency was independently associated with future risk of mild cognitive impairment and dementia among elderly individuals, especially in those whose baseline cognitive function had decreased only modestly.
Mild cognitive impairment (MCI) is an intermediate stage between the cognitive decline of aging and the cognitive decline of dementia. When one experiences MCI, they are able to continue engaging in basic activities of daily living and they are at an increased risk of dementia.
Many studies have shown a relationship between low vitamin D levels and an increased risk of dementias in older adults. However, the association between low vitamin D levels and MCI has not been thoroughly evaluated.
Researchers recently investigated the association between vitamin D status and the risk of MCI and dementia in older adults. A total of 412 participants from the Korean Longitudinal Study on Health and Aging (KLoSHA) who completed a series of cognitive function evaluations in 2005-2006 and 2010-2011 were included in the study. KLoSHA was created to further the understanding of geriatric diseases of Korean elderly adults ages 65 and over.
Cognitive function was assessed using various tests, including the Mini Mental State Examination (MMSE). The MMSE is a 30-point questionnaire used to measure the severity and progression of cognitive impairment. A maximum of 30 points is possible and a score above 27 considered normal. The MMSE tests multiple mental abilities including memory, attention, and language.
The researchers also used other standardized tests to supplement the MMSE in diagnosing MCI and dementia.
Here is what the researchers found after comparing baseline vitamin D status to the development of MCI and dementia:
- After five years, 338 participants’ cognitive function remained the same, whereas 67 participants showed progression to MCI or dementia.
- The progression of cognitive impairment was significantly associated with baseline vitamin D status (p = 0.046).
- Out of the 236 participants who had a baseline MMSE score below 27, severe vitamin D deficiency, as defined by levels less than 10 ng/ml, was independently associated with the progression of cognitive impairment (p = 0.025).
- The participants with a MMSE score below 27 and were severely vitamin D deficient were 7.13 times more likely to develop MCI than those with vitamin D levels of 20 ng/ml or higher (p = 0.012).
The researchers concluded,
“Here for the first time we have demonstrated that a low vitamin D status increased the risk of MCI as well as dementia in this prospective study with a community-based cohort of the elderly.”
They continued by discussing the implications of their findings,
“Moreover, our results suggest that vitamin D status can be a useful clinical marker for selecting groups at risk of developing MCI as well as dementia.”
The researchers adjusted for a wide variety of confounding factors, including but not limited to, physical activity, age, sex, stroke, and depressive mood. Therefore, the results are less likely to have occurred due to reverse causality.
There are a few limitations to keep in mind when looking at this study. As the researchers pointed out, among the initial 1000 subjects in the KLoSHA study, about 50% did not participate in the 5 year follow up. This could have led to selection bias. Also, the vitamin D levels were only measured once during the study. Vitamin D levels could have easily fluctuated over the span of 5 years.
Future cohorts should include a larger study population and should measure vitamin D levels throughout the entire study to further our understanding of the role of vitamin D in the progression of dementia and MCI.