In the study, the research team did a cross-sectional examination of 1,766 people age 65 and older in the Health Survey for England 2000. Each person had his blood vitamin D measured, and each was tested for cognitive impairment with the Abbreviated Mental Test Score.
It was found that 212 of the 1,766, or 12 percent, were cognitively impaired. Normal subjects had the highest levels of blood vitamin D, while fully half of the cognitively impaired had the lowest levels of the vitamin.
In an analysis that ruled out the influence of other variables, the researchers found that participants with the lowest levels of blood vitamin D were 2.3 times, or 130 percent, more likely to suffer cognitive impairment than their high-vitamin-D counterparts.
Evidence from test-tube and animal studies shows that vitamin D has a protective effect on nerves – but how that happens is unknown. What is known is that many cells – including neurons and glia (nervous-system cells that support, protect, nourish and insulate neurons) – have receptors for the vitamin. The Llewellyn team said there is growing “evidence for previously unsuspected roles for vitamin D in brain development and neuroprotection.”
They called for further research to determine whether high blood vitamin D levels protect against cognitive impairment in more diverse populations, and to find if vitamin D supplements provide a shield against memory disorders.