Objectives: To determine whether subclinical vitamin D deficiency in Indian children under 5 y of age is a risk factor for severe acute lower respiratory infection (ALRI).

Design: A hospital-based case-control study.

Setting: Sanjeevani Paediatrics Hospital, a private hospital in Indapur, India.

Participants: A total of 150 children including 80 cases and 70 controls, aged 2–60 months, were enrolled. Case definition of severe ALRI as given by the World Health Organization was used for cases. Controls were healthy children attending outpatients' service for immunization.

Main outcome measure: Association of serum 25-hydroxyvitamin D3 (25OHD3) with severe ALRI, controlling for demographic and other potential risk factors.

Results: Serum 25OHD3 increased with age. Factors significantly associated with decreased risk of severe ALRI in univariate analysis were: exclusive breastfeeding in the first 4 months (cases 35/78 (45%), controls 41/64 (64%); P= 0.02); introduction of other dietary liquids than milk only after 6 months (cases 46/70 (66%), controls 31/66 (47%); P= 0.03); use of liquid petroleum cooking fuel (cases 32/80 (40%), controls 40/70 (57%); P= 0.04); infant not covered in swaddling cloths when exposed to sunlight before crawling (cases 11/52 (21%), controls 25/54 (46%); P= 0.006); and serum 25OHD3> 22.5 nmol/l (cases 16/80 (20%), controls 48/70 (69%); P< 0.001). In multivariate analysis, factors associated with significantly lower odds ratio for having severe ALRI were: serum 25OHD3> 22.5 nmol/l (OR: 0.09; 95% CI 0.03–0.24; P< 0.001) and exclusive breastfeeding in the first 4 months of life (OR 0.42; 95% CI 0.18–0.99; P= 0.046) with age and height/age as significant covariates.

Conclusion: Subclinical vitamin D deficiency and nonexclusive breastfeeding in the first 4 months of life were significant risk factors for severe ALRI in Indian children.