Study finds low vitamin D levels linked to poorer neuropsychological function but not dementia

Posted on: March 18, 2016   by  Amber Tovey

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Researchers from the Boston University School of Medicine recently discovered that vitamin D status is linked to poorer neurological skills but not dementia or Alzheimer’s disease.

With a growing elderly population, dementia has become more prevalent. Approximately one in 14 people over the age of 65 and one in six over the age of 80 are affected by dementia. Thus, it’s of the utmost importance to find modifiable risk factors for dementia.

Some research has suggested that low vitamin D status increases one’s risk for dementia. However, much of this research has been from cross-sectional and case control study designs. Drawing conclusions from these studies are difficult, because individuals with cognitive impairment may have pre-existing risk factors for low vitamin D status, such as older age and limited outdoor activity.

Prospective cohort studies have the ability to associate vitamin D levels to future risk of dementia. A prospective cohort study from the past year found that the cognitive ability of individuals with low vitamin D status declined three times greater than those with levels above 20 ng/ml. While these results were impressive, further studies are warranted to validate these findings.

In a recent prospective cohort study, researchers hypothesized that low vitamin D status would be associated with impairment in executive function and an increased risk of dementia. To test this hypothesis, they looked at the sample population from the Original and Offspring Framingham Heart Study. The Original cohort began in 1948 with participants examined every two years. The Offspring cohort started in 1971, comprised of the individuals from the Original cohort along with their spouses.

The researchers compared vitamin D status to the incidence of dementia among 1,663 individuals ages 60 years or older at the time of vitamin D measurement. They also looked at neuropsychological skills and hippocampal volume. Low hippocampal volume has been shown to be a predictive marker of dementia. Hippocampal atrophy, or waste, accelerates as dementia begins to develop. All individuals were free from dementia at baseline and the majority were Caucasian.

Various neuropsychological tests were used, including the Trail Making Test and the Hooper Visual Organization Test. The Trail Making Test evaluates the ability of visual attention, executive functioning and task switching. The test involves connecting a set of 25 dots as quickly as possible while still maintaining accuracy. The Hooper Visual Test evaluates visual perceptual skills by presenting individuals with a line drawing of a common object that has been broken into fragments, and asking them to name what the object would be if reassembled.

Here is what the researchers found:

  • Over a 9 year follow-up, 16.1% developed dementia, out of which 12.5% developed AD specifically.
  • 8% of individuals from the cognitive sample were considered vitamin D deficient defined by levels less than 10 ng/ml.
  • Vitamin D deficiency was associated with poorer performance on Trail Making B-A and the Hooper Visual Organization Test (p = 0.02, 0.05).
  • Vitamin D deficiency was associated with lower hippocampal volumes, but not total brain volume.
  • No association was found between vitamin D deficiency and all-cause dementia or Alzheimer’s disease.

The researchers concluded,

“The current study adds support to a growing body of literature implicating vitamin D deficiency in the development of neuropsychological impairment and subclinical brain injury. Correcting vitamin D deficiency through diet, lifestyle change or supplementation may potentially help prevent brain injury and cognitive decline.”

They continued by stating,

“However, we did not find an association between levels of vitamin D and the risk of dementia or clinically characterized AD in the Framingham Heart Study.”

The study has several strengths, including its large sample size and long follow-up. However, there are also a few limitations to consider. The study population was mostly comprised of white Caucasians, which limits the generalizability of our findings to other ethnic groups. Lastly, the study could not prove causality.

Citation

Tovey, A. & Cannell, JJ. Study finds low vitamin D levels linked to poorer neuropsychological function but not dementia. The Vitamin D Council Blog & Newsletter, March, 2016.

Source

Karakis, I. et al. Association of Serum Vitamin D with the Risk of Incident Dementia and Subclinical Indices of Brain Aging: The Framingham Heart Study. Journal of Alzheimer’s Disease, 2015.

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