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Multicenter Study
. 2011 Mar;20(3):464-72.
doi: 10.1158/1055-9965.EPI-10-1220. Epub 2011 Jan 25.

Obesity and thyroid cancer risk among U.S. men and women: a pooled analysis of five prospective studies

Cari M Kitahara  1 , Elizabeth A Platz, Laura E Beane Freeman, Ann W Hsing, Martha S Linet, Yikyung Park, Catherine Schairer, Arthur Schatzkin, James M Shikany, Amy Berrington de González
Affiliations
Multicenter Study

Obesity and thyroid cancer risk among U.S. men and women: a pooled analysis of five prospective studies

Cari M Kitahara et al. Cancer Epidemiol Biomarkers Prev. 2011 Mar.

Abstract

Background: Thyroid cancer incidence has risen dramatically in the United States since the early 1980s. Although the prevalence of obesity has doubled during this time period, the relationship between obesity and thyroid cancer is uncertain.

Methods: We examined the association between body mass index (BMI) and thyroid cancer risk in a pooled analysis of five prospective U.S. studies, including 413,979 women and 434,953 men. Proportional hazards models with attained age as the time metric were adjusted for education, race, marital status, smoking, alcohol intake, and (where appropriate) cohort and sex.

Results: Over follow-up (mean=10.3 years), 768 women and 388 men were diagnosed with thyroid cancer. The risk of thyroid cancer was greater with increasing BMI [per 5 kg/m2: HR in women, 1.16 (95% CI, 1.08-1.24); HR in men, 1.21 (95% CI, 0.97-1.49)]. There was no significant heterogeneity between studies (both P>0.05). For women and men combined, the HRs for overweight (25.0-29.9 kg/m2) and obesity (≥30 kg/m2) compared with normal-weight (18.5-24.9 kg/m2) were 1.20 (95% CI, 1.04-1.38) and 1.53 (95% CI, 1.31-1.79), respectively. We found no significant effect modification by other factors, and the results did not differ significantly by histologic type. A significant positive association for BMI in young adulthood (ages 18-20) with thyroid cancer risk was also observed [per 5-kg/m2 increase: HR, 1.18 (95% CI, 1.03-1.35)].

Conclusion: BMI was positively associated with thyroid cancer risk in both men and women.

Impact: Our study provides strong evidence that obesity is an independent risk factor for thyroid cancer.

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Figures

Figure 1
Figure 1. Multivariable-adjusted HRsa and 95% CIs for BMI (per 5 kg/m2) and thyroid cancer risk by sex: pooled analysis
Squares and horizontal lines correspond to the study-specific HRs and 95% CIs, respectively. The size of a square reflects the study-specific weight, and the diamond represents the pooled HR and 95% CI. The vertical dotted line represents the pooled HR. The abbreviations of the studies are same as in table 1. Abbreviations: BMI=body mass index, CI= confidence interval, HR= hazards ratio aAdjusted for education, race, marital status, cigarette smoking, and alcohol intake bCalculated using a random effects model cHeight and weight were measured directly
Figure 1
Figure 1. Multivariable-adjusted HRsa and 95% CIs for BMI (per 5 kg/m2) and thyroid cancer risk by sex: pooled analysis
Squares and horizontal lines correspond to the study-specific HRs and 95% CIs, respectively. The size of a square reflects the study-specific weight, and the diamond represents the pooled HR and 95% CI. The vertical dotted line represents the pooled HR. The abbreviations of the studies are same as in table 1. Abbreviations: BMI=body mass index, CI= confidence interval, HR= hazards ratio aAdjusted for education, race, marital status, cigarette smoking, and alcohol intake bCalculated using a random effects model cHeight and weight were measured directly
Figure 2
Figure 2. Multivariable-adjusted HRsa and 95% CIs for BMI categories and thyroid cancer risk: aggregate analysis
Abbreviations: BMI=body mass index, CI= confidence interval, HR= hazards ratio aAdjusted for sex, education, race, marital status, cigarette smoking, alcohol intake, and cohort
Figure 3
Figure 3. Multivariable-adjusted HRsa and 95% CIs for BMI (per 5 kg/m2) and thyroid cancer risk, stratified by selected risk factors: aggregate analysis
Abbreviations: BMI=body mass index, CI= confidence interval, HR= hazards ratio *Test for interaction calculated using the likelihood ratio test comparing a model with a cross-product term to a model without **Test for interaction calculated using the Mantel-Haenszel test for heterogeneity aAdjusted for sex, education, race, marital status, cigarette smoking, alcohol intake, and cohort bCalculated using a random effects model
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