Dietary Inflammatory Index and Differentiated Thyroid Carcinoma Risk

A Population-Based Case-Control Study in New Caledonia

Melanie Paquet; Nitin Shivappa; James R. Hébert; Dominique Baron-Dubourdieu; Marie-Christine Boutron-Ruault; Pascal Guénel; Thérèse Truong

Disclosures

Am J Epidemiol. 2020;189(2):95-107. 

In This Article

Abstract and Introduction

Abstract

Despite research efforts, current knowledge of the etiology of thyroid carcinoma remains limited. To explore the potential role of diet-induced inflammation, we examined the association between differentiated thyroid cancer risk and the energy-adjusted Dietary Inflammatory Index (E-DII) in a population-based case-control study conducted in New Caledonia, a Pacific archipelago with one of the highest recorded thyroid cancer incidence rates in the world. The E-DII was computed from food frequency questionnaire information on usual dietary intake. Logistic regression analyses were performed on data from 324 histologically confirmed cases of papillary or follicular carcinoma, diagnosed from 1993 to 1999, and 402 controls. Positive associations between E-DII and thyroid cancer risk were observed (comparing extreme tertiles, odds ratio = 1.67, 95% confidence interval: 1.08, 2.58; P for trend = 0.002), with stronger associations found for larger carcinomas (P for trend = 0.0005). Stratified analyses showed an increased risk of thyroid cancer associated with the E-DII among Southern province residents (P for trend = 0.003), Melanesian women (P for trend = 0.02), obese participants (P for trend = 0.006), and ever-smokers (P for trend = 0.0005). Our results suggest that a proinflammatory diet—especially when concomitant with other inflammation-inducing conditions or habits (e.g., obesity, smoking)—is associated with increased risk of thyroid carcinoma.

Introduction

Exceptionally high incidence rates of differentiated thyroid cancer (DTC) have been reported in New Caledonia, a French territory in the South Pacific.[1,2] Incidence rates were highest in the 1995–1999 period, with sex-specific rates of 8 per 100,000 men and 63 per 100,000 women[1]—compared with rates in ranges of approximately 1–5 per 100,000 men and 2–8 per 100,000 women in other high-income countries.[2] As elsewhere around the world, improved sensitivity of tumor detection techniques was likely a major,[3] albeit not the only,[1,4] contributor to the spike in incidence.

New Caledonia is divided into 3 provinces (Northern, Southern, and the Loyalty Islands) and includes the following communities in descending order by size: Melanesian (Kanak), European, Polynesian, and Asian. In New Caledonia, as in other countries, striking ethnic and geographic disparities in DTC incidence rates can be observed. Indeed, Melanesian women, in particular those living in the Loyalty Islands, are at very high risk of developing DTC.[1] Lifestyle, genetic, and environmental risk factors have been hypothesized.[5–7] However, studies have yet to fully explain the elevated incidence rates observed in this ethnic group or province.

Exposure to ionizing radiation, particularly during childhood, is the only well-established risk factor for DTC.[8] With regard to New Caledonia, such exposure is considered unlikely, because no nuclear tests were conducted in this Pacific territory. The closest such tests were carried out in the Republic of the Marshall Islands and French Polynesia (located, respectively, 3,700 kilometers and 5,500 kilometers away).

Research on the role of dietary factors in DTC etiology has largely focused on foods that interfere with thyroid function (e.g., foods with high iodine concentration or containing goitrogenic substances). But, so far, these studies have yielded inconsistent results.[9–11] An area for further exploration of the possible impact of dietary habits on DTC risk is the inflammatory potential of overall diet.

Chronic inflammation is known to play an integral part in tumor initiation, progression, and malignant conversion.[12] While a direct contribution of inflammation has been established for certain cancer types (e.g., gastric cancer), the relationship between inflammation and DTC appears particularly complex and is still under study. In line with the oft-reported observation of lymphocytic and macrophage infiltration of thyroid tumors,[13] epidemiologic evidence to date suggests an association between DTC and systemic inflammatory conditions, such as thyroid autoimmune diseases (e.g., Hashimoto's thyroiditis)[14,15] and obesity.[16,17] Some serum inflammatory biomarkers have also been found linked to DTC (e.g., C-reactive protein and interleukin (IL)-6, IL-7, IL-8, IL-10, and IL-13).[18–23] However, many of these associations, derived primarily from relatively small case-control studies, have been inconsistently reported.

There is growing evidence of the impact of diet on chronic inflammation. Dietary components have been shown to have pro- or antiinflammatory properties via modulation of inflammatory biomarker levels.[24,25] Based on such observations, the Dietary Inflammatory Index was developed as a tool for quantifying inflammation derived from an individual's overall diet.[26]

To our knowledge, this study is the first attempt to assess dietary inflammation in relation to thyroid carcinoma risk. The objective was to examine the association between the energy-adjusted Dietary Inflammatory Index (E-DII) and DTC risk in an archipelago-wide case-control study conducted in New Caledonia.

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