Mercury exposure raises diabetes risk later in life

By Sally Robertson, B.Sc.Mar 1 2013

People with a high level of mercury exposure in young adulthood are at an increased risk for developing diabetes later in life, report researchers.

Their analysis of data from the Coronary Artery Risk Development in Young Adults (CARDIA) trial showed that mercury exposure, as determined from toenail concentrations of the metal, was dose-dependently associated with risk for diabetes among 3875 American adults.

The findings also suggest that increased mercury exposure may be associated with pancreatic islet ß-cell dysfunction, report Ka He (Indiana University, Bloomington, USA) and colleagues.

Among the participants, who were aged 18-30 years at baseline (1987), median values of toenail mercury across quintiles were 0.073, 0.0139, 0.213, 0.332, and 0.607 µg/g.

During an 18-year follow up, 288 participants developed diabetes, as defined by a glycated hemoglobin level of 6.5% or more, a fasting plasma glucose of 7.0 mmol/L or more, a nonfasting plasma glucose of 11.1 mmol/L or more, or a postprandial 2-hour plasma glucose of 11.1 mmol/L or more on an oral glucose tolerance test.

As reported in Diabetes Care, a positive but nonsignificant association was found between toenail mercury level and diabetes risk, after adjustment for demographic and major lifestyle variables, notably body mass index (BMI).

However, this association became significant after further adjustment for intake of long-chain n-3 polyunsaturated fatty acids (LCn-3PUFAs) and magnesium, and for toenail selenium.

Compared with participants in the lowest quintile of toenail mercury levels, those in the highest quintile had a 1.65-fold greater risk for developing diabetes, after full adjustment for confounders.

Furthermore, individuals with higher mercury exposure also had increased fasting glucose and insulin levels, increased Homeostasis Model of Assessment-Insulin Resistance (HOMA-IR), and a decreased HOMA ß-cell function index. However, only the association with HOMA ß-cell function index was significant.

"MEHG [methylmercury] is a major contaminant in some fish, and toenail mercury is generally correlated with fish consumption," notes the team. "While LCn-3PUFAs, largely derived from fish consumption, are considered to be the key nutrients responsible for the potential benefits of fish intake, fish is also a good dietary source of selenium and magnesium," they add.

The team suggests that the potential adverse effects of consuming mercury through diet may be attenuated by such nutrients, and that researchers studying contaminants such as mercury should consider confounding from other components in fish.

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