Adiposity, metabolites, and colorectal cancer risk: Mendelian randomization study
Authors: Bull Caroline J. , Bell Joshua A. , Murphy Neil , Sanderson Eleanor , Smith George Davey , Timpson Nicholas J. , Banbury Barbara L. , Albanes Demetrius , Berndt Sonja I. , Bézieau Stéphane , Bishop D Timothy T. , Brenner Hermann , Buchanan Daniel D. , Burnett-Hartman Andrea , Casey Graham , Castellví-Bel Sergi , Chan Andrew T. , Chang-Claude Jenny , Cross Amanda J. , de la Chapelle Albert , Figueiredo Jane C. , Gallinger Steven J. , Gapstur Sue M. , Giles Graham G. , Gruber Stephen B. , Gsur Andrea , Hampe Jochen , Hampel Heather , Harrison Tabitha A. , Hoffmeister Michael , Hsu Li , Huang Wen-Yi , Huyghe Jeroen R. , Jenkins Mark A. , Joshu Corinne E. , Keku Temitope O. , Kühn Tilman , Kweon Sun-Seog , Le Marchand Loic , Li Christopher I. , Li Li , Lindblom Annika , Martín Vicente , May Anne M. , Milne Roger L. , Moreno Victor , Newcomb Polly A. , Offit Kenneth , Ogino Shuji , Phipps Amanda I. , Platz Elizabeth A. , Potter John D. , Qu Conghui , Quirós J. Ramón , Rennert Gad , Riboli Elio , Sakoda Lori C. , Schafmayer Clemens , Schoen Robert E. , Slattery Martha L. , Tangen Catherine M. , Tsilidis Kostas K. , Ulrich Cornelia M. , van Duijnhoven Franzel JB. , Van Guelpen Bethany , Visvanathan Kala , Vodicka Pavel , Vodickova Ludmila , Wang Hansong , White Emily , Wolk Alicja , Woods Michael O. , Wu Anna H. , Campbell Peter T. , Zheng Wei , Peters Ulrike , Vincent Emma E. , Gunter Marc J. 
Published: March 2020

Importance

Evidence on adiposity altering colorectal cancer (CRC) risk differently among men and women, and on metabolic alterations mediating effects of adiposity on CRC, is unclear.

Objective

To examine sex- and site-specific associations of adiposity with CRC risk, and whether adiposity-associated metabolites explain associations of adiposity with CRC.

Design

Two-sample Mendelian randomization (MR) study.

Setting

Genetic variants from expanded genome-wide association studies of body mass index (BMI) and waist-to-hip ratio (WHR, unadjusted for BMI; N=806,810), and 123 metabolites (mostly lipoprotein subclass-specific lipids) from targeted nuclear magnetic resonance metabolomics (N=24,925), were used as instruments. Sex-combined and sex-specific MR was conducted for BMI and WHR with CRC risk; sex-combined MR was conducted for BMI and WHR with metabolites, for metabolites with CRC, and for BMI and WHR with CRC adjusted for metabolite classes.

Participants

58,221 cases and 67,694 controls (Genetics and Epidemiology of Colorectal Cancer Consortium; Colorectal Cancer Transdisciplinary Study; Colon Cancer Family Registry).

Main outcome measures

Incident CRC (overall and site-specific).

Results

Among men, higher BMI (per 4.2 kg/m2) was associated with 1.23 (95%-confidence interval (CI)=1.08, 1.38) times higher CRC odds (inverse-variance-weighted (IVW) model); among women, higher BMI (per 5.2 kg/m2) was associated with 1.09 (95%-CI=0.97, 1.22) times higher CRC odds. Higher WHR was more strongly associated with CRC risk among women (IVW-OR=1.25, 95%-CI=1.08, 1.43 per 0.07-ratio) than men (IVW-OR=1.05, 95%-CI=0.81, 1.36 per 0.07-ratio). BMI or WHR was associated with 104 metabolites (false-discovery-rate-corrected P≤0.05) including low-density lipoprotein (LDL) cholesterol, but these metabolites were generally unassociated with CRC in directions consistent with mediation of adiposity-CRC relations. In multivariable MR, associations of BMI and WHR with CRC were not attenuated following adjustment for representative metabolite classes – e.g. the univariable IVW-OR of BMI for CRC was 1.12 (95%-CI=1.00, 1.26), and 1.11 (95%-CI=0.99, 1.26) adjusting for LDL lipids.

Conclusions and relevance

Our results suggest that higher BMI more greatly raises CRC risk among men, whereas higher WHR more greatly raises CRC risk among women.

Adiposity was associated with numerous metabolic alterations, but none of these alterations explained associations between adiposity and CRC. More detailed metabolomic measures are likely needed to clarify mechanistic pathways.