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Abstract
Background A number of antioxidant defences counteract potentially damaging oxidising species within the respiratory tract. Many enzymes, such as the superoxide dismutases and glutathione peroxidases, require essential elements to maintain function. Vitamins A, C and E also have antioxidant properties. It has been suggested that asthmatic patients are deficient in antioxidants. This study assessed levels of serum antioxidants, markers of airways inflammation and resultant oxidative stress burden with increasing severity of asthma.
Method This is a case control study comparing patients with severe asthma (BTS steps 4/5) to mild corticosteroids-naïve asthmatics and normal healthy controls. Participants were assessed in terms of asthma diagnosis, severity, exhaled breath condensate (EBC) nitrite, fractional exhaled nitric oxide (feNO), spirometry, and serum copper, zinc, selenium, vitamin A and vitamin E measurements. Analyses were conducted using Kruskal-Wallis, one way analysis of variance.
Results The severe asthma group was comprised of 30 patients (23 females, mean age 41.4 years [range 19 to 56], mean FEV1 2.2 litres [% predicted 72.2%], mean FEV1/FVC ratio 72.7%, mean daily inhaled corticosteroid equivalent to 2,390 µg BDP, with 17/30 [57%] on maintenance oral corticosteroids). Fifteen mild and corticosteroid naïve patients were recruited (9 females, mean age 34.6 years [range 19–57], mean FEV1 3.48l [% predicted 100.5%], FEV1/FVC ratio 82.2%). All 15 were treated with salbutamol only. The control group was comprised of 15 patients (12 females, mean age 37.6 years [range 25–52], mean FEV1 3.53 [%predicted 111.7%], and FEV1/FVC ratio 81.9%). FeNO increased significantly with increasing severity (p = 0.001), but EBC nitrite did not (p = 0.9). Vitamin A and E levels increased significantly with increased disease severity (p = 0.04 and 0.0008 respectively). There was no significant difference between groups with copper (p = 0.98), zinc (p = 0.8) or selenium (p = 0.9).
Conclusion We observed no evidence of deficiency in the serum minerals or vitamins in the severe asthmatics with increased FeNO but not EBC nitrite. We conclude that impaired oxidative stress defences in severe asthma may be driven by factors other than vitamin or mineral deficiency.
Vitamin levels across severity groups