Vitamin D is well known for its role in bone health and calcium homeostasis. However, emerging evidence suggests that vitamin D may also have an influence on other health issues such as type 2 diabetes, cardiovascular disease, cancer, autoimmune diseases and respiratory function( 1 , 2 ). Chronic obstructive pulmonary disease (COPD) is characterised by airflow limitation and is associated with an abnormal inflammatory response( 3 ). It has been hypothesised that vitamin D deficiency may enhance chronic airway and systemic inflammation and increase the risk of infectious exacerbations( 1 ) in COPD. Vitamin D status in this population is, therefore, of interest. The aim of the present study was to examine the prevalence of sub-optimal vitamin D status in a sample of patients with moderate to severe COPD and to compare the vitamin D status of a sub-sample of this patient group with healthy age-, sex-, and season-matched controls.
The serum 25-hydroxyvitamin D (25-OHD) levels of 81 Northern Irish patients with moderate to severe COPD (classified according to Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines( 3 )) were measured using Ultra Performance Liquid Chromatography followed by tandem mass spectrometry (UPLC/MS/MS). Twenty-two COPD patients were matched for age-, sex-, and season of blood sample collection with healthy participants recruited from Northern Ireland at the same time as the COPD cohort.
The mean vitamin D status for male and female COPD patients was 35.3 (sd 23.3) nmol/l and 38.5 (sd 49.6) nmol/l, respectively (P=0.701; Independent samples t-test). There was no significant difference in mean vitamin D status between those with moderate (32.3 (sd 20.2) nmol/l) compared to severe COPD (39.8 (sd 44.8) nmol/l) (P=0.372; Independent samples t-test). Season of blood sample collection had no significant effect on vitamin D status in this group of COPD patients (P=0.116; analysis of variance). Overall, almost half of the COPD patients (45.7%) were vitamin D deficient (<25 nmol/l), with 79% showing biochemical evidence of sub-optimal vitamin D status (<50 nmol/l). Only 10% of this sample had adequate vitamin D concentrations (>75 nmol/l). The vitamin D status of patients with moderate to severe COPD (n=22) was significantly lower compared with healthy age-, sex-, and season-matched controls (n=22) (36.7 (sd 36.8) nmol/l versus 52.5 (sd 23.2) nmol/l, respectively; P=0.003; Independent samples t-test).
Suboptimal vitamin D status was prevalent in this sample of patients with moderate to severe COPD. Furthermore, patients with moderate to severe COPD had significantly lower vitamin D concentrations compared to healthy age-, sex-, and season-matched controls. The potential role of vitamin D supplementation in the prevention or management of COPD is worthy of further investigation.