In a remarkable study conducted over two decades, researchers have shown a link between iodine intake and longevity in older adults. The study, conducted in the Danish cities of Randers and Skagen, found that living in an iodine-rich environment is associated with increased longevity.
The cities of Randers and Skagen, located just 140 kilometers apart on the Jutland peninsula in Denmark, differ greatly in the iodine content of their drinking water. While Randers has an average iodine content of 2 micrograms per liter, the iodine content in Skagen is 139 micrograms per liter. These differences are due to the different source rocks of the aquifers from which drinking water is obtained.
The study began in 1997-1998 by examining residents born in Randers in 1920 and in Skagen between 1918 and 1923. The researchers collected baseline data through questionnaires, performed physical examinations, and measured iodine concentrations in spot urine samples. Participants were tracked through December 31, 2017.
The results showed that Skagen residents had significantly longer life spans than Randers residents. Cox regression showed that living in Skagen was associated with a lower risk of death compared with Randers, both in age- and sex-adjusted analyses and after adjustment for age, sex, number of medications, Charlson comorbidity index, smoking, alcohol, and income.
Researchers suggest that iodine intake influences the incidence of thyroid disease. Hyperthyroidism is more common in mildly and moderately iodine-deficient populations, whereas iodine-rich populations may have a higher incidence of hypothyroidism. Hyperthyroidism can lead to complications such as atrial fibrillation, heart failure, and increased fracture risk. These complications are associated with increased mortality, especially in vulnerable groups such as older adults.
The study suggests that long-term residency in an iodine-rich environment may be associated with increased longevity compared with residency in an iodine-deficient environment. However, the researchers emphasize that further studies are needed to confirm these findings and understand the exact mechanisms leading to this increased longevity.