January 23, 2019
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Metabolic status, sex influence obesity-related thyroid cancer risk

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Thyroid cancer risk is significantly higher for men with increased BMI regardless of metabolic health, whereas women with metabolically healthy obesity are not at elevated risk compared with normal-weight women, according to findings published in Thyroid.

“Obesity is a known risk factor for several cancers, such as breast cancer, endometrial cancer, colon cancer and prostate cancer, suggesting that obesity can affect cancer incidence,” Seungho Ryu, MD, PhD, from the department of occupational and environmental medicine at Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine in Seoul, South Korea, and colleagues wrote. “The mechanisms underlying the association between obesity and thyroid cancer have not yet been elucidated, but obesity-related metabolic abnormalities have been proposed to mediate their associations. ... Different phenotypes of obesity may help our understanding of whether obesity per se or the presence of coexisting metabolic abnormalities can increase thyroid cancer risk.”

Ryu and colleagues conducted a longitudinal cohort study of 255,051 adults (mean age, 38 years; 43% women) from the Kangbuk Samsung Healthy Study. All participants underwent annual health examinations at Kangbuk Samsung Hospital Total Healthcare Screening clinics in Seoul and Suwon, South Korea, from 2002 to 2014 and had at least one follow-up visit before December 2017.

Participants were grouped into four weight groups based on BMI: underweight (< 18.5 kg/m2), normal weight (18.5 kg/m2 to 22.9 kg/m2), overweight (23 kg/m2 to 24.9 kg/m2) and obese ( 25 kg/m2). Waist circumferences of 90 cm or more in men and 85 cm or more in women were used to define abdominal obesity.

Participants were considered metabolically unhealthy if they had a fasting glucose level of 100 mg/dL or more, blood pressure of 130/85 mm Hg or more, a triglyceride level of 150 mg/dL or more, low HDL cholesterol (< 40 mg/dL in men; < 50 mg/dL in women), insulin resistance or any combination of the factors, including using glucose-lowering agents and lipid-lowering agents.

Thyroid cancer diagnosis was self-reported via a structured questionnaire during the baseline visit and any follow-up examinations.

In a median follow-up of 5.3 years, 1,037 men and 1,890 women developed thyroid cancer, making for rates of 1.3 and 3.2 per 1,000 person-years, respectively.

Using participants in the normal-weight group as reference, metabolically healthy men with overweight (HR = 1.12; 95% CI, 0.86-1.46) or obesity (HR = 1.47; 95% CI, 1.12-1.93) were at increased risk for thyroid cancer. The same was true for metabolically unhealthy men with overweight (HR = 1.02; 95% CI, 0.82-1.27) or obesity (HR = 1.26; 95% CI, 1.03-1.53).

In women, metabolically unhealthy status had a greater effect on thyroid cancer development. Specifically, metabolically unhealthy women with overweight (HR = 1.18; 95% CI, 0.99-1.41) or obesity (HR = 1.43; 95% CI, 1.22-1.69) had higher HRs for thyroid cancer compared with metabolically healthy women with overweight (HR = 1.1; 95% CI, 0.91-1.32) or obesity (HR = 1.05; 95% CI, 0.8-1.36).

The researchers also examined the effect of waist circumference on thyroid cancer risk. Participants were divided into four quartiles based on their waist circumference, with the first quartile representing the smallest measurements and used as reference.

Metabolically healthy men in the third (HR = 1.42; 95% CI, 1-2.02) and fourth (HR = 1.15; 95% CI, 0.71-1.87) quartile had higher risk than those in the lowest quartile, whereas the risk was comparatively higher for the second (HR = 1.28; 95% CI, 0.93-1.77), third (HR = 1.43; 95% CI, 1.05-1.95) and fourth (HR = 1.6; 95% CI, 1.17-2.17) quartile in metabolically unhealthy men. Metabolically healthy women in the second (HR = 1.06; 95% CI, 0.87-1.31), third (HR = 1.15; 95% CI, 0.93-1.43) and fourth (HR = 1.21; 95% CI, 0.95-1.55) quartile of waist circumference were all at increased risk compared with the first quartile. A similar result was found in metabolically unhealthy women in the second (HR = 1.27; 95% CI, 0.92-1.77), third (HR = 1.54; 95% CI, 1.13-2.1) and fourth (HR = 1.8; 95% CI, 1.33-2.44) quartile.

“Our findings indicate that obesity, abdominal obesity and metabolic health may differently affect the development of thyroid cancer by sex,” the researchers wrote. “Sex differences in fat distribution can affect the development of thyroid cancer. Men predominantly store fat in the visceral area, while women tend to store fat predominantly in the gluteal-femoral region. Additionally, recent studies addressing the different roles of upper-body and lower-body fat in metabolism have suggested disease-protective effects of lower-body fat.” – by Phil Neuffer

Disclosure s : The authors report no relevant financial disclosures.