Numerous studies have reported the health benefits of vitamin D. Now, a new study has reported that a deficiency of the vitamin may accelerate cognitive decline in older adults. The findings were published online in the journal JAMA Neurology by researchers at Rutgers University in New Brunswick, New Jersey, and University of California, Davis in Davis, California.
The study authors note that past studies have reported that approximately half of the US population over age 65 has insufficient or deficient levels of vitamin D, and that non-whites are more likely to have low levels. Therefore, they conducted a study to examine the relationship between vitamin D status and changes in cognitive function in a group of ethnically diverse older adults.
The study group comprised 382 seniors who were enrolled in an outpatient clinic enrolled between February 2002 and August 2010. Their cognitive function was evaluated at baseline and yearly thereafter. Serum vitamin D level was measured; vitamin D deficiency was defined as the following: deficient, less than 12 ng/mL; insufficient, 12 to less than 20 ng/mL; adequate, 20 to less than 50 ng/mL; or high, 50 ng/mL or higher. Cognitive function was evaluated via the Spanish and English Neuropsychological Assessment Scales. Associations were evaluated between vitamin D levels and course of cognitive decline.
The researchers found that at baselined, the 382 seniors had an average age of 75.5 years; 61.8% were women; and 41.4% were Caucasian, 29.6% were African American, 25.1% were Hispanic, and 3.9% were other race/ethnicity. Diagnosis at enrollment included 17.5% of the seniors had dementia, 32.7% had mild cognitive impairment, and 49.5% were cognitively normal. The average vitamin D level was 19.2 (11.7) ng/mL; 26.2% of the subjects were vitamin D deficient and 35.1% were vitamin D insufficient. The average vitamin D levels were significantly lower for African Americans and Hispanics compared to Caucasians. The average vitamin D levels were lower in the dementia group compared with the mild cognitive impairment and cognitively normal groups. The average follow-up was 4.8 years.
Low vitamin D levels were also associated with significantly more difficulty with remembering general information (semantic memory), seeing the relationship between objects (visuospatial ability) and managing overall thinking processes (executive function). Over a period of slightly less than five years, seniors with low vitamin D levels had a more rapid decline in executive function and in the ability to remember their own past personal experiences (episodic memory).
These rates of decline were similar for individuals who had normal brain function at the beginning of the study and for those who already had dementia or mild cognitive impairment.
The authors concluded that a low vitamin D level was associated with accelerated decline in cognitive function in ethnically diverse older adults, including African American and Hispanic individuals who exhibited a high prevalence of vitamin D insufficiency or deficiency. They cautioned that it remains to be determined whether vitamin D supplementation can slow cognitive decline.
The National Institutes of Health recommends the following amounts of vitamin D supplements:
Birth to 12 months: 400 IU
Children 1–13 years: 600 IU
Teens 14–18 years: 600 IU
Adults 19–70 years: 600 IU
Adults 71 years and older: 800 IU
Pregnant and breastfeeding women: 600 IU
There is a potential danger in consuming too much vitamin D as a supplement. The upper tolerable level of daily intake for vitamin D is 4,000 IU/day for individuals age 9 years and older. Above this level, the risk of adverse health effects increases, with very high doses (10,000 IU/day or more) potentially causing damage to kidneys and other tissues.