Vitamin D status is associated with muscle strength and quality of life in patients with COPD: a seasonal prospective observation study

Abstract

Emma L Carson,1 L Kirsty Pourshahidi,1 Sharon M Madigan,2 Francina R Baldrick,1 Martin G Kelly,3 Eamon Laird,4 Martin Healy,5 JJ Strain,1 Maria S Mulhern1 1Nutrition Innovation Centre for Food and Health (NICHE), School of Biomedical Sciences, University of Ulster, Coleraine, Co. Londonderry, UK; 2Respiratory Dietitian, Pulmonary Rehabilitation Team, Belfast Health and Social Care Trust, Belfast, UK; 3Respiratory Team, Altnagelvin Hospital, Western Health and Social Care Trust, Londonderry, UK; 4School of Medicine, Trinity College, Dublin, Ireland; 5Department of Biochemistry, Central Pathology Laboratory, St James Hospital, Dublin, Ireland Background: Owing to hospitalization, reduced functional capacity and consequently, less sunlight exposure, suboptimal vitamin D status (25-hydroxyvitamin D [25(OH)D]<50 nmol/L) is prevalent among COPD patients. Objective: This study aimed to investigate seasonal changes in vitamin D status and any associated changes in fat-free mass (FFM), muscle strength and quality of life (QoL) in COPD patients. Patients and methods: COPD patients living in Northern Ireland (n=51) completed study visits at the end of winter (March/April) and at the end of summer (September/October), corresponding to the nadir and peak of vitamin D status, respectively. At both time points, serum concentration of 25(OH)D was quantified by liquid chromatography-tandem mass spectrometry, FFM (kg) was measured using bioelectrical impedance and muscle strength (kg) was measured using handgrip dynamometry. QoL was assessed using the validated St George’s Respiratory Questionnaire. Results: Mean±SD 25(OH)D concentration was significantly higher at the end of summer compared to the end of winter (52.5±30.5 nmol/L vs 33.7±28.4 nmol/L, P<0.001); and housebound patients had significantly lower 25(OH)D concentration compared to nonhousebound patients at the end of summer (42.9±4.2 vs 57.2±9.9 nmol/L; P<0.001). Muscle strength (at both time points) and QoL (end of summer only) were positively predicted by 25(OH)D concentration, independent of age, sex and smoking status. Conclusion: This study highlights the need for health policies to include a recommendation for year-round vitamin D supplementation in housebound COPD patients, and wintertime supplementation in nonhousebound patients, to maintain optimal 25(OH)D concentrations to protect musculoskeletal health. Furthermore, an optimal vitamin D status may have potential benefits for QoL in these patients. Keywords: vitamin D, COPD, muscle strength, quality of life, seasonal, 25(OH)D

Keywords

• Vitamin D
• COPD
• muscle strength
• quality of life
• seasonal
• 25(OH)D