OBJECTIVE -Magnesium deficiency has been associated with insulin resistance (IR) and increased risk for type 2 diabetes in adults. This study was designed to determine whether obese children exhibit serum or dietary magnesium deficiency and its potential association with IR.RESEARCH DESIGN AND METHODS -We studied 24 obese nondiabetic children (BMI Ն85th percentile) and 24 sex-and puberty-matched lean control subjects (BMI Ͻ85th percentile). We measured serum magnesium, indexes of insulin sensitivity, dietary magnesium intake (using a food frequency questionnaire), and body composition (by air displacement plethysmography).RESULTS -Serum magnesium was significantly lower in obese children (0.748 Ϯ 0.015 mmol/l, means Ϯ SE) compared with lean children (0.801 Ϯ 0.012 mmol/l) (P ϭ 0.009). Serum magnesium was inversely correlated with fasting insulin (r s ϭ Ϫ0.36 [95% CI Ϫ0.59 to Ϫ0.08]; P ϭ 0.011) and positively correlated with quantitative insulin sensitivity check index (QUICKI) (0.35 [0.06 -0.58]; P ϭ 0.015). Dietary magnesium intake was significantly lower in obese children (obese: 0.12 Ϯ 0.004 vs. lean: 0.14 Ϯ 0.004 mg/kcal; P ϭ 0.003). Dietary magnesium intake was inversely associated with fasting insulin (Ϫ0.43 [Ϫ0.64 to Ϫ0.16]; P ϭ 0.002) and directly correlated with ; P ϭ 0.002).CONCLUSIONS -The association between magnesium deficiency and IR is present during childhood. Serum magnesium deficiency in obese children may be secondary to decreased dietary magnesium intake. Magnesium supplementation or increased intake of magnesium-rich foods may be an important tool in the prevention of type 2 diabetes in obese children. Diabetes Care 28:1175-1181, 2005T he current epidemic of childhood obesity has been associated with an alarming rise in the prevalence of pediatric type 2 diabetes (1). Hyperinsulinemia and insulin resistance (IR) are the precursors of type 2 diabetes. Obesity and dietary macronutrients clearly play a role in the risk for type 2 diabetes, but the role of micronutrients in this process is not clear.Magnesium is an important cofactor for enzymes involved in carbohydrate metabolism. A strong relationship between magnesium and insulin action has been reported (2,3). In adults, low serum and intracellular magnesium concentrations are associated with IR, impaired glucose tolerance, and decreased insulin secretion (4 -6). Furthermore, large epidemiologic studies in adults indicate that lower dietary magnesium and lower serum magnesium are associated with increased risk for type 2 diabetes (7,8). However, the role of magnesium deficiency in the development of IR during childhood has not been clearly defined. The present study was designed to determine whether a relationship exists between magnesium homeostasis and IR in obese children and to evaluate potential mechanisms leading to magnesium deficiency in these children.RESEARCH DESIGN AND METHODS -We studied 24 obese children (BMI Ն85th percentile for age and sex) aged 8 -17 years with at least one risk factor for type 2 diabetes and 24 lean children...