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 was 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. Thyroid stimulating hormone (TSH), free thyroxine (fT4), free triiodothyronine (fT3), thyroglobulin (TG) and thyroglobulin antibody (TGAb) 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/24h in East Greenland and 169 µg/24h 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 to 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.