Recently, the prevalence of colorectal neoplasm is increasing sharply. It has been reported that both colorectal neoplasm and cardiovascular disease share similar common risk factors. Subclinical hypothyroidism (SCH) occurs in 4–20% of the adult population and is an independent risk factor for cardiovascular disease. However, no study has yet explored the relationship between SCH and colorectal neoplasm. Our objectives were to clarify the association between the two conditions.

This is a case-control study. A total of 273 cases of colorectal neoplasm were first identified, and a 1:3 matched random sample of 819 controls was then collected using strata according to age, and gender. The medical records of all these patients were retrieved. Blood pressure, body mass index, and thyroid function were determined. Colonoscopies were performed by experienced gastroenterologists. A logistic regression analysis was carried out to explore the relationship between SCH and colorectal neoplasm.

Remarkably, the prevalence rate of SCH was significantly higher in colorectal neoplasm (+) group, compared with colorectal neoplasm (−) group (P<0.01). Colorectal neoplasm was found in 67 (34.9%) subjects in SCH group, which was more than that in euthyroid group (P=0.002). Moreover, patients with SCH were more likely to have advanced colonic lesion and colorectal cancer compared with euthyroid subjects (P=0.028 and 0.036, respectively). After adjusting for the factors of blood pressure, body mass index, history of hypertension and smoking, an association still existed between colorectal neoplasm and SCH (OR=1.689, 95% CI: 1.207–2.362, P=0.002).

A strong association between SCH and colorectal neoplasm was firstly identified. SCH was found to be an independent risk factor for colorectal neoplasm.