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


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


CONCLUSIONS
Our study provides strong evidence that obesity is an independent risk factor for thyroid cancer.
Radiation Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, NIH, Rockville, MD 20852, USA. kitaharac@mail.nih.gov
Cari M
CM
Kitahara
Elizabeth A
EA
Platz
Laura E Beane
LE
Freeman
Ann W
AW
Hsing
Martha S
MS
Linet
Yikyung
Y
Park
Catherine
C
Schairer
Arthur
A
Schatzkin
James M
JM
Shikany
Amy
A
Berrington de González
D015992:Body Mass Index; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology*; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D013964:Thyroid Neoplasms / Q000453:epidemiology*; D014481:United States / Q000453:epidemiology
Cancer Epidemiol Biomarkers Prev. 2009 Mar;18(3):784-91
19240234
Cancer Causes Control. 2009 Jul;20(5):581-90
19043789
Cancer. 2010 Feb 1;116(3):544-73
19998273
Int J Cancer. 2010 Jun 15;126(12):2984-90
19950225
World Health Organ Tech Rep Ser. 1995;854:1-452
8594834
Obes Rev. 2001 Aug;2(3):141-7
12120099
Br J Cancer. 2006 Aug 7;95(3):366-70
16832414
Arch Intern Med. 2008 Mar 24;168(6):587-92
18362250
Psychol Methods. 2006 Jun;11(2):193-206
16784338
Am J Epidemiol. 2010 Jan 15;171(2):242-52
19951937
Br J Cancer. 2005 Oct 31;93(9):1062-7
16234822
Control Clin Trials. 2000 Dec;21(6 Suppl):273S-309S
11189684
Endocr Relat Cancer. 2009 Dec;16(4):1251-60
19528244
Thyroid. 2008 Feb;18(2):141-4
18279014
Control Clin Trials. 1986 Sep;7(3):177-88
3802833
BMC Cancer. 2008 Feb 28;8:63
18307811
Cancer Causes Control. 2008 Dec;19(10):1233-42
18618280
Am J Epidemiol. 2001 Dec 15;154(12):1119-25
11744517
Cancer Causes Control. 2000 Feb;11(2):137-44
10710197
Clin Endocrinol (Oxf). 2006 Feb;64(2):125-8
16430708
Cancer Causes Control. 2006 Sep;17(7):901-9
16841257
Gastroenterology. 2007 May;132(6):2087-102
17498505
J Natl Cancer Inst. 2009 Mar 4;101(5):296-305
19244173
Environ Health Perspect. 1998 Aug;106(8):427-36
9681969
Cancer Epidemiol Biomarkers Prev. 1997 Nov;6(11):863-73
9367058
J Clin Oncol. 2005 Jul 20;23(21):4742-54
16034050
Am J Epidemiol. 2009 Jul 1;170(1):53-64
19403842
Am J Epidemiol. 2007 Nov 15;166(10):1140-9
17855390
Best Pract Res Clin Endocrinol Metab. 2008 Aug;22(4):659-69
18971125
Lancet. 2008 Feb 16;371(9612):569-78
18280327
Int J Cancer. 2010 Jun 15;126(12):2947-56
19795465
Clin Endocrinol (Oxf). 2005 Apr;62(4):487-91
15807881
Br J Cancer. 2009 Nov 3;101(9):1630-4
19862001
Environ Health Perspect. 1998 Aug;106(8):447-57
9681971
Gend Med. 2009;6 Suppl 1:60-75
19318219
Ethn Dis. 2008 Spring;18(2 Suppl 2):S2-151-4
18646339
Diabetologia. 2006 May;49(5):945-52
16557372
Environ Health Perspect. 1996 Apr;104(4):362-9
8732939
Cancer. 1992 Jan 15;69(2):586-98
1728391