Thyroid cancers potentially preventable by reducing overweight and obesity in Australia: A pooled cohort study

Abstract

Thyroid cancer incidence and the prevalence of overweight and obesity are increasing, but the future thyroid cancer burden attributable to contemporary levels of overweight and obesity has not been evaluated before. We quantified this burden in Australia, and assessed whether the overweight/obesity‐attributable burden differed by sex or other population subgroupings. We estimated the strength of the associations of overweight and obesity with thyroid cancer with adjusted proportional hazards models using pooled data from seven Australian cohorts (N = 367 058) with 431 thyroid cancer cases ascertained from linked national cancer registry data during a maximum 22‐year follow‐up. We combined these estimates with nationally representative 2017 to 2018 estimates of overweight and obesity prevalence to estimate population attributable fractions (PAFs) of future thyroid cancers attributable to overweight and obesity, accounting for competing risk of death, and compared PAFs for population subgroups. Contemporary levels of overweight and obesity explain 18.6% (95% confidence interval [CI] = 5.2%‐30.2%), and obesity alone 13.7% (95% CI: 5.2%‐21.4%), of the future thyroid cancer burden. The obesity‐attributable thyroid cancer burden is 21.4% (95% CI: 2.8%‐36.5%) for men and 10.1% (95% CI: 0.8%‐18.6%) for women. Were the currently obese overweight instead, 9.9% (95% CI: 1.0%‐18.1%) of thyroid cancers could be avoided. The relative overweight/obesity‐attributable burden is higher for those consuming on average more than two alcoholic drinks per day (63.4%) and for those who are not married/co‐habiting (33.2%). In conclusion, avoiding excess weight, especially obesity, should be a priority for thyroid cancer prevention. Further studies, with findings stratified by tumour size, may reveal the potential role of overdiagnosis in our results.

Anthropometric, dietary, and lifestyle factors and risk of advanced thyroid cancer: The NIH‐AARP diet and health cohort study

“…Using national population‐based health survey and cancer registry data, the authors estimated that 15% of papillary thyroid cancers (and 60% of large papillary thyroid cancers) diagnosed in the United States are attributable to overweight and obesity. A subsequent study conducted in Australia yielded similar estimates of attributable risk 30 …”

An ecological study of obesity-related cancer incidence trends in Australia from 1983 to 2017

“…Despite this, approximately 19% of thyroid cancer cancers have been attributed to overweight and obesity. 45 , 46 Surveillance programs for liver cancer facilitate an earlier diagnosis rather than increasing incidence rates. 47 Increases can be attributed to key risk factors including viral hepatitis infection and alcohol consumption alongside overweight and obesity.…”

Obesity and thyroid cancer risk

“…Multiple studies have also investigated whether the relationship between obesity and thyroid cancer varies by sex, but results are conflicting. Some have reported a stronger association between obesity and thyroid cancer in women [12,13,15 ▪▪ ,32,33], whereas others found a stronger association in men [8,11,14,16,18 ▪ ,34]. The reasons for the conflicting results are not clear but could be due to body composition differences between females and males across different populations, including how this is modified by age and menopausal status or different measures of adiposity.…”

“…In 2016, the IARC judged thyroid cancer to be one of 13 cancers where the absence of body fatness lowers cancer risk [7]. The IARC primarily cited the findings of Kitahara et al [8], however several large cohort studies and meta-analyses demonstrated the association prior to this [9–13], and subsequently [14,15 ▪▪ ,16,17,18 ▪ ].…”

“…Recent studies have estimated the proportion of thyroid cancer cases that could be avoided if obesity was eliminated (population attributable fraction – PAF) [14,18 ▪ ]. An Australian study estimated that almost one in five future thyroid cancers will be attributable to current levels of overweight and obesity and that reducing BMI from the obese to the overweight range could avoid ten percentage of future thyroid cancers in Australia [18 ▪ ]. Estimates from the United States suggest that the proportion of thyroid cancer cases attributable to overweight/obesity increased from 11.4% to 16.2% between 1995–2015 [14].…”