Thyroid autoimmunity in Greenlandic Inuit.

Objective: This study aimed to provide the first data on the occurrence of thyroid autoimmunity among Inuit in Greenland, a distinct ethnic group who is not iodine deficient. Design: This study is a population-based cross-sectional study. Methods: Data were collected in Nuuk in West Greenland and in Ammassalik district in East Greenland. Information on lifestyle, diet and diseases was obtained using questionnaires. Thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TGAb) and thyroid-stimulating hormone (TSH) were measured in serum. Iodine and creatinine were measured in spot urine samples. Results: The participation rate was 95% with 434 Inuit participants; 75% were smokers. Iodine excretion was 169 µg/24 h in urban West Greenland, 224 µg/24 h in the main town and 228 µg/24 h in settlements in rural East Greenland. TPOAb, TgAb or either of these was measured in the serum from 3.7, 5.9 and 8.3% of participants, respectively. TPOAb or TgAb was found in 9.3% of Inuit women and 7.5% of men and more frequently, in East Greenland Inuit with the higher iodine excretion (P = 0.02). There was some evidence suggesting that thyroid autoimmunity was more frequent among non-smokers (12.5%) compared to smokers (7.0%). Harbouring a thyroid autoantibody was most frequent in participants with TSH above 3.6 mIU/L (P < 0.001). Conclusion: Thyroid autoantibodies were rare among Greenland Inuit. While iodine nutrition was associated with autoimmunity similarly to other ethnic groups, the influence of sex and smoking was limited. This could suggest genetic component in Inuit, but the impact of cold, selenium and persistent organic pollutants needs to be elucidated.

Mortality in Greenlanders with chronic hepatitis B virus infection.

In-depth reviewing of all medical records and clinical databases concluded a 7-year shorter lifespan among Greenlanders infected with hepatitis B virus (HBV) compared with non-infected. Mortality did not associate with liver disease or any other specific disease entity. A possible mechanism for the reduced lifespan is subclinical inflammation that may be augmented by chronic viral infection. We hypothesized that chronic HBV infection contributes to this process causing a reduced life span. We added measurement of two markers of inflammation to the 10-year follow-up on our study of HBV among 50- through 69-years-old subjects in Greenland. The markers were YKL40 related to liver disease and hsCRP as a global marker of inflammation. Survival was evaluated using Cox regression with time until death entered as dependent variable and age, sex, smoking, alcohol intake, BMI, the presence of HBsAg and one marker of inflammation as explanatory variables. Forty-eight percent of participants with chronic HBV infection were alive after 10 years compared with 65% of participants without infection (p = 0.003). Survival associated with age (p < 0.001), BMI (p = 0.003) and both YKL40 and hsCRP (both, p < 0.001). Harbouring HBV influenced 10-year survival in the Cox regression after adjusting for age, sex, BMI, smoking, alcohol intake and inflammation. In conclusion, chronic low-grade inflammation and being infected with HBV were independent markers of mortality in otherwise healthy subjects. Thus, the 7-year shorter lifespan among Greenlanders with chronic HBV infection seems related to the long-lasting infection. Our findings call for caution in perceiving a chronic infection as benign.

Adaptation to a High Iodine Intake in Greenland Inuit Suggested by Thyroid Disease Pattern.

Objective: Arctic living is influenced by cold winters, short summers, and excessive iodine intake from the traditional Inuit diet providing for habitation of the Arctic for centuries. This is changing and we surveyed thyroid function in populations living in Greenland. Design: Population-based cross-sectional study. Methods: Data were collected in the capital city in West Greenland and in rural East Greenland. Information on lifestyle, dietary habits, and medical history was obtained using questionnaires. Thyrotropin, free thyroxine, free triiodothyronine, thyroglobulin, and thyroglobulin antibody were measured in serum, iodine, and creatinine in spot urine samples. Results: One percent of the Greenlandic population was invited and 535 participated with an overall participation rate of 95%. Iodine excretion was 225 µg/24 hours in East Greenland and 169 µg/24 hours among West Greenland Inuit. Hyperthyroidism occurred in 10.7% of West Greenlandic Inuit (men/women: 4.3%/16.3%) and 7.8% of East Greenlandic Inuit (3.8%/12.8%). Hypothyroidism was found in 2.7% in West Greenland (0.0%/5.0%) and 5.6% (5.6%/5.6%) in East Greenland. Conclusion: Hyperthyroidism was frequent among Inuit and the occurrence of hypothyroidism was low. The pattern of hyper- and hypothyroidism among Greenlandic Inuit with adequate iodine intake was comparable with those seen in populations with iodine deficiency. Inuit may thus have adapted to excessive iodine intake over centuries, causing a need for a higher iodine intake to prevent iodine deficiency disorders.

Iodine in Edible Seaweed, Its Absorption, Dietary Use, and Relation to Iodine Nutrition in Arctic People.

Dietary iodine is important to human health, and both low and high iodine intake levels increase the risk of disease. Seaweed is rich in iodine and it is a common component in both Asian and in Arctic cuisines. While the intake and impact are known for Asian people, data are lacking for Arctic people. We aimed to (1) measure iodine content of dietary seaweeds in Greenland, (2) estimate iodine absorption, and (3) assess the impact on iodine intake in Arctic people. A hunter in East Greenland donated household seaweed for (1) measurement of iodine content and (2) ingestion of 45 g by each of eight individuals with subsequent urine collections. (3) In Ammassalik, 96% of 50-69-year-old Inuit reported on the frequency of intake of seaweed and provided a spot urine sample for iodine measurement. Seaweed species provided were Chondrus crispus and Ascophyllum nodosum. (1) The iodine content was 47 and 102 mg/g, respectively. (2) An estimated 1.1 and 1.9 mg of the ingested 2.1 and 4.6 of iodine in seaweed were excreted in the urine within 2 days. (3) More than two in three Inuit reported some dietary use, and 41% (109 of 268) reported a weekly intake of dietary seaweed, which was associated with iodine excretion. In conclusion, the iodine content of edible seaweeds in the Arctic is very high and bioavailable. Dietary intake contributed to the recommended iodine intake level, but marked variation in iodine excretion calls for evaluation of the impact on thyroid function.

Serum 25-hydroxyvitamin D, calcium and parathyroid hormone levels in Native and European populations in Greenland.

Ca homoeostasis is important to human health and tightly controlled by powerful hormonal mechanisms that display ethnic variation. Ethnic variations could occur also in Arctic populations where the traditional Inuit diet is low in Ca and sun exposure is limited. We aimed to assess factors important to parathyroid hormone (PTH) and Ca in serum in Arctic populations. We included Inuit and Caucasians aged 50-69 years living in the capital city in West or in rural East Greenland. Lifestyle factors were assessed by questionnaires. The intake of Inuit diet was assessed from a FFQ. 25-Hydroxyvitamin D (25OHD2 and 25OHD3) levels were measured in serum as was albumin, Ca and PTH. The participation rate was 95 %, with 101 Caucasians and 434 Inuit. Median serum 25OHD (99·7 % was 25OHD3) in Caucasians/Inuit was 42/64 nmol/l (25, 75 percentiles 25, 54/51, 81) (P<0·001). Total Ca in serum was 2·33/2·29 mmol/l (25, 75 percentiles 2·26, 2·38/2·21, 2·36) (P=0·01) and PTH was 2·7/2·2 pmol/l (25, 75 percentiles 2·2, 4·1/1·7, 2·7) (P<0·001). The 69/97 Caucasians/Inuit with serum 25OHD <50 nmol/l differed in PTH (P=0·001) that rose with lower 25OHD levels in Caucasians, whereas this was not the case in Inuit. Ethnic origin influenced PTH (ß=0·27, P<0·001) and Ca (ß=0·22, P<0·001) in multivariate linear regression models after adjustment for age, sex, BMI, smoking, alcohol and diet. In conclusion, ethnic origin influenced PTH, PTH response to low vitamin D levels and Ca levels in populations in Greenland. Recommendations are to evaluate mechanisms underlying the ethnic influence on Ca homoeostasis and to assess the impact of transition in dietary habits on Ca homoeostasis and skeletal health in Arctic populations.

A national study on weight classes among children in Greenland at school entry.

OBJECTIVES: To estimate the proportion of gender-specific thinness, overweight and obesity among children born in 2005 at school entry in Greenland and to compare figures between the capital, Nuuk, with the rest of Greenland. STUDY DESIGN: A cross-sectional study based on data from Electronic Medical Records (EMR). METHODS: All children born in 2005 with permanent address in Greenland at the time of data extraction with a registered weight and height in EMR from January 1st 2011 to January 31st 2013 were included in the study. Information about height without shoes and weight in light indoor clothing was obtained. Body Mass Index (BMI) was calculated. Participants were categorized into age and gender-specific weight classes based on the International Obesity Task Force (IOTF) cut-offs for child overweight, obesity and thinness. RESULTS: A total of 842 children born in 2005 were identified. Of those, 72% (N=607, 308 boys and 299 girls) had a recorded weight and height in the study period. In total, 74.6% (71.2-78.1) were categorized as of normal weight. The proportion of children with overweight was 15.8% (12.9-18.7) while 6.8% (4.8-8.8) were obese. In all, 2.9% were categorized as thin. The proportion of overweight among boys (12.7%) was lower (p=0.031) than among girls (19.1%), and boys in Nuuk had a lower median BMI compared to the rest of Greenland. No differences in distribution of age and gender-specific overweight and obesity were observed between the capital and the rest of Greenland. CONCLUSION: Nearly 1 quarter of Greenlandic children are overweight or obese at school entry. No differences were observed between Nuuk and the rest of Greenland. Information about weight and height is available in the EMR for the majority of all children at school entry in Greenland. Continuous monitoring of the proportion of overweight and obesity among children using data from the EMR in Greenland is recommended.