title: Severe vitamin D deficiency: a biomarker of exacerbation risk? : a reply to Heulens.
authors: Ken M
authors: KM
authors: Kunisaki
authors: Dennis E
authors: DE
authors: Niewoehner
authors: John E
authors: JE
authors: Connett
mesh_terms: D005260:Female; D006801:Humans; D008297:Male; D029424:Pulmonary Disease, Chronic Obstructive / Q000209:etiology*; D014807:Vitamin D / Q000031:analogs & derivatives*; D014808:Vitamin D Deficiency / Q000150:complications*
chemical_list: D014807:Vitamin D