Influência da variação sazonal no status de 25-hidroxivitamina D de adultos com síndrome metabólica de uma região do Brasil com elevados índices de radiação ultravioleta

Abstract

The risk of metabolic syndrome can be influenced by inadequate vitamin D levels, and exposure to sunlight is the main external source of vitamin D. This study assessed the influence of environmental, biological and nutritional factors as a function of seasons on the 25OHD status among individuals with metabolic syndrome. A cross-sectional study was developed with 180 adult and elderly individuals of both genders, between 18-80 years of age, with metabolic syndrome according to the National Cholesterol Education Program Adult Treatment Panel III (NCEP-ATP III) criteria. The 25OHD concentration was considered dependent variable; the independent variables were age, gender, skin color, use of sunscreen, skin type, sun exposure score, ultraviolet index (UVI), geographic location, season, body mass index (BMI), waist-hip ratio (WHR), waist circumference (WC), parathyroid hormone (PTH) level, total serum calcium level, and diet levels of calcium and vitamin D. The potential predictors for the 25OHD levels were investigated using 16 univariate linear regression models and seven multiple regression models. Measures of association and correlation were established and statistical significance was assumed for P < 0.05 (5%). The 25OHD status differed significantly between winter and summer (P = 0.017). The average 25OHD level was insufficient during the winter (25.89 ± 7.61 ng/mL) and sufficient during the summer (31.81 ± 10.22 ng/mL), with an increase of 5.59 ng/mL in the summer. In the simple linear regression model, 25OHD concentration was significantly associated with the summer season (P = 0.003); the season variable explained 4.2% of the variability in 25OHD concentration. The sun exposure score was significantly associated with 25OHD concentration (P = 0.008), explaining 3.4% of the variability. In the multiple regression model, gender (P = 0.27), WHR (P = 0.27), sun exposure score (P = 0.006), and winter vs. summer (P = 0.004) explained 10.4% of the variation in 25OHD concentration. Men had a 25OHD concentration 3.71 ng/mL higher than that of women. An increase of 1.0 unit in the sun exposure score resulted in an increase of approximately 0.16 ng/mL on 25OHD concentration. WHR showed an inverse association with the 25OHD concentration. The summer season and sun exposure influenced the 25OHD status in individuals with metabolic syndrome living in a region of Brazil with a high ultraviolet radiation index.