Cancers attributable to excess body weight in Canada in 2010 D Zakaria, A Shaw Public Health Agency of Canada
Introduction Cancer is a huge burden in Canada: Nearly 50% of Canadians are expected to be diagnosed with cancer in their lifetime (CCS 2017) Understanding the main drivers of cancer burden is a public health priority Population attributable fractions (PAFs) can be used to quantify the proportion of cancers attributable to specific risk factors PAFs guide cancer control efforts and public health action British researchers using PAFs identified tobacco use (PAF = 19.4%), diet (PAF=9.2%), and excess body weight (PAF=5.5%) as the top three modifiable risk factors for cancer 2
Introduction Approximately 2 out of 3 Canadians (62%) are now overweight or obese based on measured BMI (CHMS, 2012/2013) 36% overweight (BMI 25 to <30 kg/m 2 ) and 26% obese (BMI 30+ kg/m 2 ) Males (70%) are more likely than females (54%) to be overweight or obese Percent overweight or obese increasing over time Potential carcinogenic mechanisms of excess body weight include: Hormonal and metabolic changes Elevated oxidative stress Inflammatory response Gastroesophageal reflux 3
Introduction Several Canadian studies have estimated the PAF for excess body weight but limitations exist: Additional cancers associated with excess body weight have been identified BMI was not adjusted for self-report height and weight None examined regional variation across the country Primary Objective Provide current, comprehensive estimates of the proportion and number of new cancer cases attributable to excess body weight in Canadian adults (aged 25+) 4
Cancers associated with excess body weight Identified by the Continuous Update Project (CUP) of the World Cancer Research Fund International CUP completes systematic reviews and meta-analyses RTCs, cohort and nested case control studies Adjusted for confounding and show dose-response Strict criteria for including studies and conclusions are made by an independent expert panel Strong evidence of causal relationship between high BMI and 12 cancers sites 5
Cancers associated with excess body weight 6
Methods Relative risk of cancer from excess body weight Used sex specific relative risk estimates from CUP cohort results Converted RR estimates associated with a 5-unit increase in BMI to a 1-unit increase By assuming a linear relationship between natural log of RR and BMI e (Ln(RR for a 5kg/m2))/5 Males: RR = 1.02 (pancreatic, rectal, advanced prostate) to RR = 1.09 (esophageal adenocarcinoma) Females: RR = 1.01 (rectal, ovarian) to 1.08 (esophageal adenocarcinoma, uterus) 7
Relative risks associated with a one-unit increase in BMI by sex 8
Methods Prevalence of excess body weight (BMI 25+kg/m 2 ) from Canadian Community Health Survey (CCHS) Population based, self report survey, covers 97% of population over aged 12+ High response rate = 84.7% in 2000/2001 Used BMI from 2000/2001 survey to allow for latency period Correction factor applied developed using measured height and weight Weighted estimates to acknowledge sampling design Number of new cancer cases in Canada Canadian Cancer Registry (CCR), 2010 Last year of complete national data Used international rules for multiple primaries (IARC) Defined cancers associated with excess body weight using CUP meta-analysis definition 9
Analysis Population attributable fractions (PAF) = P ow (RR ow -1)/1+(P ow (RR ow -1)) P ow (proportion of the population that is overweight or obese) RR ow (relative risk of cancer due to being overweight or obese) Where RR( ow )= RR (medbmi-21) Number of cases attributable to excess body weight = PAF (for cancer type, region, sex, and age group) X Number of cases ( cancer type, region, sex, age group ) 10
Results Excess body weight (2001/2002) Approximately 55% of the Canadian population was overweight or obese Males (40%) more likely than females (30%) to be overweight Equally likely to be obese (20%) Overweight and obesity varies by province Lowest in BC and Quebec Highest in Atlantic region and Prairies Cancers attributable to excess body weight (2010) 5.7% of all cancers cases attributable to excess body weight Equivalent to 9645 cases PAF was higher in females (6.5%) versus males (4.9%) Equivalent to 5395 cases (females) and 4255 cases (males) 11
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Results PAF extremely high for some cancers But does not always result in large number of cancer cases Males, highest PAFs 42% of esophageal adenocarcinomas 25% of kidney cancers 20% of gastric cardia, liver, gallbladder, and colon cancers Females, highest PAFs 36% of esophageal adenocarcinomas 35% of uterine cancers 25% of kidney and gallbladder cancers PAFs lowest in BC and Quebec, highest in Prairies and Atlantic Canada Reflects prevalence of excess body weight 13
Results Number of attributable cases: For males, highest for: Colon (n=1445), kidney (n=780) and prostate (n=515) cancers For females, highest for Uterine (n=1825), breast (n=1765) and colon (n=675) in females 14
Population attributable fractions, by sex, aged 25+, 2010 (Canada) 45 40 35 30 25 20 15 10 5 0 Esophagus Ac Gastric Cardia Liver Gallbladder Pancreas Colon Rectum Kidney Ad Prostate Breast Uterus Ovary Males Females 15
Number of cancer cases attributable to excess body weight, by sex, aged 25+, 2010 (Canada) 2000 1800 1600 1400 1200 1000 800 600 400 200 0 Esophageal AC Gastric Cardia Liver Gallbladder Pancreas Colon Rectum Kidney AD Prostate Breast Uterus Ovary Males Females 16
Strengths and limitations Additional cancers included with strong evidence of association RR acknowledged BMI distribution Corrected BMI for self-report bias BMI does not distinguish between fat and muscle or build BMI may change over time Association between BMI and cancer may vary by population Some other cancers not included may be associated with BMI Response rate for CCHS was good but still vulnerable to bias Some error likely exists plausible ranges are included in manuscript 17
Summary An estimated 6% of cancers are attributable to excessive body weight Equivalent to 9645 cancer cases per year Prevalence of excess body weight is continuing to increase Need increased awareness of the relationship between BMI and cancer Effective interventions to lower risk 18
Questions? Contact: Dianne.Zakaria@phac-aspc.gc.ca, amanda.shaw@phac-aspc.gc.ca Look for manuscript in July: http://www.phacaspc.gc.ca/publicat/hpcdp-pspmc/index-eng.php 19
Thank you!! 20