Cod liver oil intake and incidence of asthma in Norwegian adults—the HUNT study
- 1Department of Public Health and General Practice, Norwegian University of Science and Technology, Trondheim, Norway
- 2Department of Epidemiology and Community Medicine, University of Ottawa, Ottawa, Ontario, Canada
- 3Department of Emergency Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA
- Correspondence to Dr Xiao-Mei Mai, Department of Public Health and General Practice, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim 7491, Norway;
- Received 18 April 2012
- Revised 14 August 2012
- Accepted 15 August 2012
- Published Online First 12 September 2012
Background Cod liver oil is an important source of vitamin D, but also contains other fat-soluble components such as vitamin A. Before 1999, the cod liver oil formula in Norway contained a high concentration of vitamin A (1000 µg per 5 ml). High vitamin A status is associated with increased risks of several chronic diseases.
Objective To investigate the association between cod liver oil intake and asthma development.
Methods In the Nord-Trøndelag Health Study, a total of 25 616 Norwegian adults aged 19–55 years were followed up from 1995–1997 to 2006–2008. Current analysis based on 17 528 subjects who were free of asthma and had complete information on cod liver oil intake at baseline. Cod liver oil intake was defined as daily intake ≥1 month during the year prior to baseline. Incident asthma was reported as new-onset asthma during the 11-year follow-up.
Results Of the 17 528 subjects, 18% (n=3076) consumed cod liver oil daily for ≥1 month over the past year. Cod liver oil intake was significantly associated with incident asthma with an OR of 1.62 (95% CI 1.32 to 1.98) after adjustment for age, sex, daily smoking, physical activity, education, socio-economic status, family history of asthma, and body mass index (BMI). The positive association was consistent across age (<40/≥40 years), sex (men/women), family history of asthma (yes/no) and BMI subgroups (<25/≥25 kg/m2).
Conclusions Intake of cod liver oil with high vitamin A content was significantly associated with increased incidence of adult-onset asthma.