Asthma-COPD overlap (ACO) is a new entity in the world of respiratory ailments. The respiratory tract of these patients are continuously exposed to oxidants (due to cigarette smoking) causing oxidative stress. Antioxidant enzymes such as, superoxide dismutase (SOD) and catalase (CAT) neutralize these oxidants or free radicals and transform them into safer. Vitamin D is a natural antioxidant which has few evidence of increasing antioxidant enzyme level in COPD and asthma, but not in ACO patients. To evaluate the effects of vitamin D3 supplementation on antioxidant enzymes level in vitamin D3 deficient patients with stable ACO. The randomized controlled trial was conducted in Department of Physiology Bangabandhu Sheikh Mujib Medical University (BSMMU), Shahbag, Dhaka from March 2018 to February 2019. For this study, a total number of 40 vitamin D3 deficient (serum 25 hydroxycholecalceferol <30 ng/ml) male, stable (diagnosed patient, who was not experienced any acute exacerbation, hospitalization, urgent care visits or changes in routine medication within 4 weeks prior to study) patients with ACO of age ≥40 years was selected from the Out Patient Department (OPD) of the National Institute of Diseases of Chest and Hospital (NIDCH) and randomly grouped as A (control) and B (study). Then serum Superoxide dismutase and Catalase level of all the patients was assessed. Along with the standard pharmacological treatment of ACO (according to GOLD criteria), oral vitamin D3 (80,000 IU per week) will be supplied to the patients of the 'Study group' and placebo for 'Control group' for consecutive 26 weeks. At 26th week of follow up, all the study variables were examined. With this, all patients of both the groups were advised to continue ad lib (according to their own choice) diet. The results was expressed as mean±SD and the data was statistically analyzed by SPSS Version 16, using Independent sample 't' test (between two groups) and paired student's 't' test (between paired groups before and after intervention). In the interpretation of results, <0.05 level of probability (p) was accepted as significant.

Inclusion Criteria:

• Smoker
• Stable ACO patients
• Vitamin D3 deficieny
• Duration of ACO: 1-4 years

Exclusion Criteria:

• With acute exacerbation of any pulmonary diseases, as- respiratory tract infection, bronchiectasis,pleural effusion,tuberculosis, interstitial lung disease, pneumonectomy or pulmonary lobectomy.
• Any cardiac disease.
• Chronic liver disease
• Malignancy
• Use of drugs within 1 month prior to study, as- calcium supplement, Phenytoin, Carbamazepine, Clotrimazole, Rifampicin, Nifedipine, Spironolactone, Ritononavir, Saquinavir, Cyproterone acetate, glucocorticoids, bisphosphonate
• With biochemical evidence of - uncontrolled diabetes mellitus, renal insufficiency