Dietary inflammatory potential and differentiated thyroid carcinoma: A population-based case-control study in New Caledonia

Introduction The incidence of differentiated thyroid carcinoma (DTC) varies considerably across the world, with particularly high incidence rates in Melanesians of New Caledonia. Despite research efforts, current knowledge on the etiology of thyroid carcinoma remains limited. Exposure to ionizing radiations during childhood is a well-established environmental risk factor. Tall height and large body size have consistently been associated with DTC. The increased risk of thyroid cancer in patients with autoimmune thyroid diseases also suggests a role of chronic inflammation in disease occurrence. To explore the role of dietary components with pro- or anti-inflammatory effects, we examined the association between DTC and the Dietary Inflammatory Index (DII) - a novel diet-based score estimating diet-induced inflammation. Methods We conducted a countrywide population-based case-control study in the multiethnic population of New Caledonia during 1993–1999. The study included 324 cases with histologically confirmed papillary or follicular carcinoma and 402 population controls. Based on a food frequency questionnaire that included 117 items, we calculated a DII score for each individual. The DII score was analyzed both as a continuous and as a categorical variable (quartiles) based on the sex-specific DII distribution among controls. Odds ratios (OR) and corresponding 95% CIs were calculated using unconditional logistic regression models adjusted for age, sex, ethnic community (Melanesian, European, other), province of residence (South, North, Loyalty Islands) and body mass index. Results An increased OR of thyroid cancer was observed in subjects in the highest quartile of DII score (pro-inflammatory diet) vs. the lowest quartile (anti-inflammatory diet) (OR: 2.20; 95% CI: 1.33, 3.63; P -trend = 0.002). Higher ORs were observed among residents of the Southern province (OR: 2.67; 95% CI: 1.40, 5.08; P -trend = 0.003), among ever smokers (OR: 2.99; 95% CI: 1.34, 6.69; P -trend = 0.0005), and among obese participants (OR: 3.34; 95% CI: 1.28, 8.68; P -trend = 0.006). These findings suggest that a pro-inflammatory diet is associated with increased risk of differentiated thyroid carcinoma.