We did not screen for cardiovascular disease as potential confounder, but 10% of our patient cohort were taking angiotensin converting enzyme inhibitors, 22% of them were taking beta blockers (these patients had similar FGF23 distributions as the COPD patient without cardiovascular medication), and 14% were taking both, suggestive of some degree of cardiovascular disease. This evidence concerns the gene FGF23 and chronic obstructive pulmonary disease.