A case-control study of levothyroxine and the risk of colorectal cancer

J Natl Cancer Inst. 2010 Apr 21;102(8):568-72. doi: 10.1093/jnci/djq042. Epub 2010 Mar 19.


Levothyroxine is a synthetic T(4) hormone commonly used to treat thyroid disease. Increased incidence of mostly autoimmune thyroid disease has been associated with breast and other malignancies, and thyroid hormone levels might also be associated with risk of colorectal cancer (CRC). In this population-based matched case-control study (2566 pairs) of CRC in northern Israel, use of levothyroxine for at least 5 years was assessed using structured interviews and validated by prescription records. The analysis included use of statins, aspirin, and hormone replacement therapy; CRC family history; physical activity; vegetable consumption; ethnicity; age; and sex. All statistical tests were two-sided. The use of levothyroxine was associated with a statistically significantly reduced relative risk of CRC (odds ratio = 0.59, 95% confidence interval = 0.43 to 0.82, P = .001). This association remained statistically significant after adjustment for age, sex, use of aspirin and statins, sports activity, family history of CRC, ethnic group, and level of vegetable consumption (odds ratio = 0.60, 95% confidence interval = 0.44 to 0.81, P = .001). No statistically significant interactions were seen between use of levothyroxine and aspirin, statins, or hormone replacement therapy.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Aged
  • Case-Control Studies
  • Colorectal Neoplasms / epidemiology*
  • Colorectal Neoplasms / ethnology
  • Colorectal Neoplasms / genetics
  • Colorectal Neoplasms / prevention & control*
  • Confounding Factors, Epidemiologic
  • Female
  • Humans
  • Hypothyroidism / drug therapy
  • Israel / epidemiology
  • Jews / statistics & numerical data
  • Logistic Models
  • Male
  • Middle Aged
  • Odds Ratio
  • Research Design
  • Retrospective Studies
  • Risk Assessment
  • Risk Factors
  • Selection Bias
  • Thyroxine / therapeutic use*


  • Thyroxine