Ethnic Differences Found in Vitamin D Levels May Explain Memory Decline

Vitamin D insufficiency or deficiency is associated with an accelerated loss of cognitive functions in older adults from a variety of ethnic backgrounds. Joshua Miller, PhD, Department of Nutritional Sciences, Rutgers University, and colleagues published the findings of a study investigating the association between changes in cognitive function and vitamin D levels among ethnically diverse older adults online in JAMA Neurology on September 14, 2015.

The researchers measured serum 25-hydroxyvitamin D (25-OHD) in order to assess the participants’ level of vitamin D. They defined less than 12 ng/mL as deficient, 12 to less than 20 ng/mL as insufficient, and 20 to less than 50 ng/mL as adequate. Anything over 50 ng/mL was defined as high.

There were 382 participants, drawn from people who were enrolled in an outpatient clinic between February 2002 and August 2010. This was a longitudinal, multiethnic cohort study. The participants underwent baseline assessments and annual follow-ups. The mean age of participants was 75.5 years, with 61.8% women. Of those enrolled, the ethnic backgrounds were 41.4% white, 29.6% African American, 25.1% Hispanic, and 3.9% of other race/ethnicity.

Approximately half of the participants had either dementia or mild cognitive impairment (MCI) at the beginning of the study. The mean 25-OHD level was slightly insufficient at 19.2 ng/mL. However, the mean 25-OHD levels were “significantly lower for African American and Hispanic participants compared with white participants” at 17.9 ng/mL for African Americans, and 17.2 ng/mL for Hispanics, while it was 21.7 ng/mL for whites.

Additionally, “the baseline mean 25-OHD level was lower in individuals with dementia compared with cognitively normal individuals and those with MCI.” The researchers concluded that their study confirmed previous findings that there are significant differences in vitamin D levels among older adults with normal cognition, MCI, and dementia. The two cognitive domains most associated with dementia are episodic memory and executive function, and also the two that appear to be most affected by vitamin D insufficiency or deficiency.

This study shows that African American and Hispanic people are more likely to have a vitamin D insufficiency or deficiency, and that is associated with an accelerated decline in episodic memory and executive function. The researchers urge future clinical trials with populations of nonwhite race/ethnicity to determine whether or not vitamin D supplements could prevent dementia.