Relationship between cumulative ultraviolet exposure and cognitive function in a rural elderly Chinese population

OBJECTIVES: Some researchers have focused on the relationship between vitamin D and cognition, but the conclusions are inconsistent. We estimated cumulative UV exposure could be used to represent the individual's long-term vitamin D status and investigated its association with global cognitive function in elderly Chinese. METHODS: A total of 641 participants aged 60 years and over were recruited in a rural area of Shenyang, China. All were interviewed to obtain data regarding sociodemographic characteristics and time spent outdoors. Cognitive function was evaluated using the Montreal Cognitive Assessment-Beijing version (MoCA-BJ). Images of skin from UV-exposed (dorsal hand) and UV-protected (inner forearm) sites from each individual were graded by the Beagley-Gibson system. Differences in skin-grade between the 2 sites were used to indicate cumulative UV exposure level. Subjects were grouped in tertiles based on skin-grade differences (<1.75, 1.75-2.74, and ≥ 2.75), representing low, medium, and high UV exposure levels, respectively. The MoCA-BJ score was classified in tertiles as low (<19), middle (19-22), and high (≥23) levels of cognition. Associations between cognitive function and UV exposure were analyzed using ordinal regression. RESULTS: Skin-grade differences were associated with self-reported time spent outdoors. After adjustment for age, gender, education, BMI, whether living alone, income, diet, hypertension, and diabetes, a high UV exposure level was associated with better cognitive function (odds ratio = 0.643, 95% confidence interval = 0.427-0.969). CONCLUSIONS: Greater cumulative UV exposure appears to be associated with better cognitive function in elderly adults.