In that previous studies have suggested that Vitamin D protects against cognitive decline, and public health experts estimate that upwards of 40% of older adults are deficient in the vitamin, David J. Llewellyn, from the University of Exeter (United Kingdom), and colleagues studied 858 adults, ages 65 years and older, to examine the association between Vitamin D and cognitive decline or dementia. The team measured blood levels of  25-hydroxyvitamin D (25[OH]D), and conducted cognitive assessments, every three years for a six-year study period.  Participants were classified as “severely deficient” if the 25(OH)D level was less than 25 nanomoles per liter, as “deficient” if levels were at least 25 but below 50 nanomoles per liter, as “insufficient” if it was at least 50 but less than 75 nanomoles per liter, and as “sufficient” if it was 75 nanomoles per liter or higher. “Severe vitamin D deficiency” was found to be associated with a 60% increase in the risk of substantial cognitive decline.  Writing that: “Low levels of vitamin D were associated with substantial cognitive decline in the elderly population studied over a 6-year period,” the researchers urge that their findings “raise important new possibilities for treatment and prevention.”