Non-Essential Trace Elements Dietary Exposure in French Polynesia: Intake Assessment, Nail Bio Monitoring and Thyroid Cancer Risk.

Background: In French Polynesia, thyroid cancer mortality and incidence is reported to be the highest in the world. Excessive levels of non-essential trace elements (nETE) in the body are associated with several types of cancer. Objective: The present study aims to provide quantitative information on food contamination by mercury (Hg), lead (Pb), arsenic (As) and cadmium (Cd) in French Polynesia and its potential correlation with measurements performed in fingernails of Polynesians, and then to investigate the potential association between these nETE and different thyroid cancer risks. Methods: The study population included 229 interviewed cases and 373 interviewed controls We performed a descriptive analysis of Polynesian food and examined the association between thyroid cancer risk and daily intake levels of nETE and with fingernail nETE levels. Results: Hg contamination was mainly present in sea products, Pb contamination was present in almost all samples, Cd was detectable in starchy food and As was detectable in all sea products. No patient exceeded dietary contamination WHO limits for Pb, 2 participants exceeded it for Hg and 3 individuals (0.5%) for cadmium. In fingernail clippings, the most detectable pollutant was Pb (553 participants), then Hg (543 participants) then Cd (only in 130 participants). Thyroid cancer risk was increased more than 4 times by Pb daily intake in patients with a history of cancer in first-degree relatives than in ones without (p for interaction =0.01), and 2 times more in women with more than 3 pregnancies than in those with none or less (p for interaction =0.005); it was also increased following As intake by more than 30% in patients with a history of cancer in first-degree relatives than in ones without (p for interaction =0.05). Conclusion: Locally produced foods are not a source of nETE exposure in French Polynesia. Dieatry nETE exposure and fingernail nETE concentration are not associated to differentiated thyroid cancer risk. No correlation found between nETE dietary exposure and fingernail nETE concentration.