Vitamin D status and associated factors among Portuguese older adults: results from the Nutrition UP 65 cross-sectional study

Objectives To evaluate vitamin D status and its associated factors in Portuguese older adults from the Nutrition UP 65 study. Design Cross-sectional observational study. Participants and methods Nationwide cluster sample of 1500 Portuguese subjects >= 65 years old. Participants were classified, according to US Institute of Medicine cut-offs, as presenting normal 25-hydroxyvitamin D (25(OH) D) levels (>= 50.0 nmol/L), at risk of inadequacy (30.0-49.9 nmol/L) or at risk of deficiency (< 30 nmol/L). The association between individuals' characteristics and 25(OH) D levels was analysed through multinomial logistic regression analysis. Results Median 25(OH) D serum value was 36.1 (interquartile range (IQR): 35.5) nmol/L. According to the used cut-offs, 39.6% of participants were at risk of 25(OH) D deficiency and 29.4% were at risk of 25(OH) D inadequacy. In the adjusted model, having higher skin pigmentation and waist circumference > 88 cm for women and > 102 cm for men were associated with higher odds of 25(OH) D deficiency. Otherwise, living in Lisbon Metropolitan Area and in Madeira, 1-12 years of schooling, being married or in a common-law marriage, monthly income >= Sic 1000, alcohol consumption, medication or supplements with vitamin D supplement use, and blood samples collected in spring or summer were associated with lower odds of being at risk of 25(OH) D deficiency. In this model, season of blood sample collection, medication or supplements use, and waist circumference were the factors more strongly associated with 25(OH) D levels. Conclusions Despite using the conservative Institute of Medicine cut-offs, over two-thirds of these study participants presented inadequate 25(OH) D levels, warranting the implementation of corrective measures. Potentially modifiable factors were strongly associated with 25(OH) D levels in this study. These findings may be particularly relevant to the development of public health policies in southern European countries.