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.

Dietary iodine and thyroid cancer risk in French Polynesia: a case-control study.

BACKGROUND: French Polynesia has one of the world's highest thyroid cancer incidence rates. Iodine is suspected to play a role in this high incidence. The objective of this study was to assess whether low dietary iodine is related to a higher risk of thyroid cancer in the French Polynesian population. METHODS: A case-control study was performed among native residents of French Polynesia. It included 229 cases of differentiated thyroid cancer diagnosed between 1979 and 2004 (203 women, 26 men) matched with 371 population controls (324 women, 47 men) on the date of birth. The current study is focused on dietary iodine intake and fish consumption (food rich in iodine) and analyzed by conditional logistic regression. RESULTS: Daily dietary iodine intake was insufficient (<150 µg/day) in 60% of both cases and controls. A decreased risk of thyroid cancer was observed with a higher consumption of fish (p(trend)=0.008) and shellfish (p(trend)=0.002), and also with a higher dietary iodine intake (p(trend)=0.03). There was no significant interaction between the effects of the thyroid radiation dose and the dietary iodine intake (p=0.2). CONCLUSION: French Polynesia is a mild iodine deficiency area in which a higher consumption of food from the sea and a higher dietary iodine intake are significantly associated with a decreased risk of thyroid cancer. The quantification of this reduction requires specific investigation of iodine intake in traditional Polynesian food.

Family history of thyroid cancer and the risk of differentiated thyroid cancer in French polynesia.

BACKGROUND: Differentiated thyroid carcinoma is considered to be the nonhereditary cancer for which familial inheritance is the highest. To date, no familial aggregation analysis of this cancer has been performed in Maohi populations, which exhibit a very high incidence rate. Therefore, we evaluate the risk of differentiated thyroid cancer associated with a family history of thyroid cancer in natives of French Polynesia. METHODS: We investigated thyroid cancer incidence in the first-degree relatives of 225 cases of differentiated thyroid carcinomas diagnosed between 1979 and 2004 in patients born in French Polynesia, and 368 randomly selected population controls matched for sex and age, born and residing in French Polynesia. All but five thyroid cancers declared among relatives were validated. RESULTS: Twenty-four cases declared a family history of thyroid cancer, when compared with 11 controls. Individuals with an affected first-degree relative had a 4.5-fold (95% confidence interval [CI], 1.9-10.6) increased risk of differentiated thyroid cancer. This odds ratio (OR) was not significantly higher when a male first-degree relative was affected (OR, 10.0; 95% CI, 1.3-74.8) compared with a female (OR, 4.0; 95% CI, 1.5-10.3) and was not different for patients who had a nonaggressive thyroid microcarcinoma (OR, 3.5; 95% CI, 0.6-16.4) than those who had a larger cancer (OR, 6.0; 95% CI, 1.8-20.5). This OR was borderline significantly (p, 0.07) higher in Maohis (OR, 11.0; 95% CI, 2.4-48.8) than in individuals of mixed origin (OR, 2.1; 95% CI, 0.8-5.9). CONCLUSION: Our study shows that the familial inheritance of differentiated thyroid cancer is particularly high in Maohi populations.

Anthropometric factors in differentiated thyroid cancer in French Polynesia: a case-control study.

OBJECTIVES: French Polynesia has one of the world's highest thyroid cancer incidence rates. A case-control study among native residents of French Polynesia included 219 cases of differentiated thyroid cancers diagnosed between 1979 and 2004 (195 women/24 men) matched with 359 population controls (315 women/44 men) on the date of birth. METHODS: Anthropometric factors were analyzed by conditional logistic regression. RESULTS: The risk of thyroid cancer for women in the highest quartile of body mass index (BMI) before diagnosis and at age 18 was 2.3-fold higher (95% CI, 1.1-4.7 p = 0.04) and 2.3-fold higher (95% CI, 1.2-4.4 p < 0.01), respectively, compared with the lowest. Women who were overweight (BMI = 25-29.9 kg/m2) or obese (BMI > or = 30 kg/m2) at age 18 and before diagnosis had an increased risk compared with those with a normal lifelong weight (OR = 6.2; 95% CI, 2.5-15.5 p < 0.01). Results for excess weight appeared in similar directions for men, although the number of cases was too small to provide reliable estimates. Height was positively associated with thyroid cancer among men and women. CONCLUSION: This study shows the role of excess body weight, especially if the onset is during early adulthood, and elevated height in the risk of differentiated thyroid cancer in populations born in French Polynesia.

Menstrual and reproductive factors in the risk of differentiated thyroid carcinoma in native women in French Polynesia: a population-based case-control study.

French Polynesia has one of the world's highest incidence rates of thyroid cancer. A case-control study among native residents of French Polynesia included 201 women diagnosed with differentiated thyroid cancer before the age of 56 years, between 1981 and 2004, matched to 324 population controls on date of birth. Face-to-face interviews were conducted from 2002 to 2004. Odds ratios were calculated by using conditional logistic regression and were reported in the total group and by ethnic group ("Polynesian" vs. "mixed"). The risk of thyroid cancer increased with natural (odds ratio = 1.9) or artificial (odds ratio = 4.5) menopause compared with that associated with a premenopausal status and with number of births (p for trend = 0.03): odds ratios for one, two, three, four or five, six or seven, and eight or more births were, respectively, 0.90, 1.6, 2.3, 2.2, 2.7, and 1.7 compared with a nulliparous status. Similar results were observed for Polynesian women. No association was observed with irregular menstrual cycles, age at menopause, history of miscarriage or induced abortion, time since last birth, age at and outcome of first pregnancy, or breastfeeding. This study confirms the role of menstrual and reproductive factors in the risk of differentiated thyroid cancer in Pacific island populations.