Relationship of sedentary time, physical activity and fitness with 1,25-dihydroxyvitamin D in middle-aged sedentary adults: The FIT-AGEING study

Purpose: Potential interactions between sedentary behaviour, physical activity (PA), and physical fitness with 25-hydroxyvitamin D (25(OH)D) status have been previously suggested. However, data are scarce concerning the association between these predictors of general health and the main active metabolite of vitamin D, the 1,25-dihidroxyvitamin D (1,25(OH)(2)D). This study aimed to analyse the relationship of sedentary time, PA levels, and physical fitness (i.e., maximal oxygen uptake (VO(2)max) and muscular strength) with 1,25(OH)(2)D in middle-aged sedentary adults. Methods: A total of 73 (39 women) middle-aged sedentary adults (53.7 +/- 5.1 years old) participated in this crosssectional study. Sedentary time and PA intensity levels were objectively measured with triaxial accelerometers for 7 consecutive days. VO(2)max was determined by a maximum treadmill test. Lower and upper limb muscular strength was assessed by an isokinetic strength test and by a handgrip strength test, respectively. 1,25(OH)(2)D plasma levels were measured using a DiaSorin Liaison (R) immunochemiluminometric assay. Results: No significant relationships were found between objectively measured sedentary time, PA levels or physical fitness (i.e., VO(2)max, extension and flexion peak torque, and hand grip strength) and 1,25(OH)(2)D (all P > 0.05). All results persisted after controlling for age, sex, fat mass or energy, vitamin D, calcium, and phosphorus intake. Conclusions: In summary, our results show that vitamin D status is not affected by physical activity habits and sedentary behaviour in middle-aged sedentary adults.