BMI–mortality association: shape independent of smoking status but different for chronic lung disease and lung cancer

Abstract

Background

Besides smoking, low or high body mass index (BMI) is associated with chronic lung disease (CLD). It is unclear how CLD is associated with BMI, whether smoking interacts with this association, and how the associations differ from the patterns known for lung cancer.

Population and Methods

Our population comprised 35,212 individuals aged 14–99, who participated in population-based surveys conducted in 1977–1993 in Switzerland (mortality follow-up until 2014). We categorized smokers into never, former, light, and heavy; and BMI into underweight, normal weight, overweight, and obese. Hazard ratios (HRs) were obtained with multivariable Cox proportional hazards models.

Results

CLD mortality was strongly associated with being underweight. This was mainly due to the effect in men (HR 5.04 [2.63–9.66]) and also prevailed in never smokers (HR 1.81 [1.11–3.00]). Obesity was also associated with CLD mortality (HR men: 1.37 [1.01–1.86], women: 1.39 [0.90–2.17]), but not with lung cancer mortality. In line with lung cancer, for CLD, the BMI–mortality association followed the same shape in all smoking categories, suggesting that this association was largely independent of smoking status.

Conclusion

The shape of the BMI–mortality association was inversely linear for lung cancer but followed a U-shape for CLD. Further research should examine the potentially protective effect of obesity on lung cancer occurrence and the possibly hazardous impact of underweight on CLD development.

Keywords:

• chronic lung disease
• lung cancer
• mortality
• body mass index
• underweight
• obesity
• smoking

Acknowledgments

We thank the Swiss Federal Statistical Office for providing mortality and census data and for the support, which made the Swiss National Cohort (SNC) and this study possible. This study was supported by the Swiss National Science Foundation (grant nos 3347CO-108806, 33CS30_134273, and 33CS30_148415). The SNC was supported by the Swiss National Science Foundation (grant nos 3347CO-108806, 33CS30_134273, and 33CS30_148415). The members of the Swiss National Cohort Study Group are Matthias Egger (Chairman of the Executive Board), Adrian Spoerri and Marcel Zwahlen (all Bern), Milo Puhan (Chairman of the Scientific Board), Matthias Bopp (both Zurich), Nino Künzli (Basel), Michel Oris (Geneva), and Murielle Bochud (Lausanne).

Author contributions

DF and MB conceived the study and assisted in data analysis, design of figures and tables, and writing. SRH and MK mainly performed statistical analyses and designed tables and figures. SRH and MK assisted in writing the Materials and Methods section. MB and DF added the important background knowledge and improved the manuscript by repeated readings and rephrasing as well as critical discussions of the intellectual content. All authors critically reviewed the paper and contributed to the final version of the manuscript.

Disclosure

The authors report no conflicts of interest in this work.