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Oncology outcomes

Does body size predict the risk of many different cancers?

Recalde M, Davila-Batista V, Díaz Y, et al. · BMC medicine · 2021

Open access · cc by · source: Europe PMC

Among millions of Spanish adults, higher BMI was linked to a higher risk of many cancers, especially of the womb and kidney, and waist size predicted risk about as well as BMI.

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Study at a glance

Design
Cohort — Prospective cohort built from Catalan primary-care electronic health records (SIDIAP), Cox models with age as time scale, followed up to end of 2018
N
N=3658417 · 3,658,417 adults with a valid BMI in the main dataset; a subsample of 291,305 also had waist circumference measured
Population
Adults aged 18-100 in Catalonia, Spain, with a BMI recorded by their GP or nurse between 2006 and 2017 and no previous cancer
Outcome
First incident diagnosis of each of 26 cancer types

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Key findings

Each 5 kg/m² increase in BMI was linked to higher risk of nine cancers, most strongly cancer of the corpus uteri (hazard ratio 1.49), followed by kidney (1.16) and gallbladder/biliary cancers. For smoking-related cancers such as lung, larynx and oesophagus, low BMI looked risky, but these curves flattened out among never smokers, suggesting thinness was standing in for heavy smoking. Among never smokers, higher BMI was also linked to head and neck, brain and Hodgkin lymphoma. Waist circumference and BMI gave overlapping risk estimates for every cancer site.

Methodology

The researchers used routine primary-care records from Catalonia, where GPs and nurses measure weight, height and waist size directly. They followed 3,658,417 adults without cancer for a median of 8.3 years and linked their BMI to first diagnoses of 26 cancer types, adjusting for smoking, alcohol, type 2 diabetes, deprivation and nationality. They tested for curved (non-linear) relationships, repeated analyses in never smokers to strip out confounding by smoking, and in a subsample with waist measurements compared BMI and waist circumference head to head.

Limitations

This is observational, so residual confounding remains, and the authors had no data on diet, physical activity, reproductive history, or cancer subtype and stage. Only 62% of the adult database had a recorded BMI, raising possible selection bias, and only about 10% of participants had a waist measurement, so the BMI-versus-waist comparison applies to an older, heavier subgroup. With millions of people, even tiny hazard ratios reach significance, and cancer diagnoses in the records had only modest positive predictive value, which could bias results toward the null.

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