Vitamin D, Cognitive Function, and Gait Speed in Older Adults: a NHANES Study

Vitamin D deficiency has been linked to poor cognition and neuromuscular impairment. We evaluated the relationships of vitamin D levels with cognitive function and gait speed in older adults. The study sample included 1076 individuals (age = > 60 years) from the 2001-2002 National Health Examination Survey (NHANES). The relationships between vitamin D and cognition and gait speed were studied. Cognitive function was measured as the number of questions correct on a digit-symbol test. Gait speed was measured as seconds to walk 20 ft. Serum 25(OH)D concentrations were measured via the DiaSorin radioimmunoassay. In our study, 32% were deficient in vitamin D (< 20 ng/ml) and 43% were insufficient in vitamin D (20-29 ng/ml). Only 25% had vitamin D values in the normal range (30-100 ng/ml). The mean vitamin D level, cognition score, and gait speed were found to be 24.71 ng/ml, 48.55 number correct, and 6.80 s, respectively. The relationship between vitamin D and cognitive function was an inverted U-shaped curve. Maximum cognition score was at a vitamin D value of 28.09 ng/ml. The relationship between vitamin D and gait speed was U-shaped. Minimum walking time was at a vitamin D level of 31.42 ng/ml. Optimal vitamin D levels were similar for both cognition and gait speed. Given the high prevalence of vitamin D deficiency in the elderly, we recommend that older individuals are tested and treated to achieve 25(OH) D values at least between 28 and 30 ng/ml.