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Janssens et al1 have demonstrated the relationship between vitamin D status and lung function in patients with chronic obstructive pulmonary disease (COPD). However, in their study there was only one assessment of vitamin D status per patient. Given the minimal component of diet to vitamin D status (serum 25-hydroxyvitamin D (25(OH)D) concentration),2 it is mostly determined by sunlight exposure and has a seasonal variation in healthy individuals.3
In a study of 24 patients with COPD (mean (SD) age 69 (5.8) years and smoking history 43 (15.8) pack-years) with measurements undertaken in the same individuals at the end of summer (August/September) and winter (March/April), we …
Footnotes
Competing interests None.
Ethics approval This study was conducted with the approval of the Norfolk research ethics committee.
Provenance and peer review Not commissioned; not externally peer reviewed.