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OBJECTIVES: To evaluate the frequency of impaired glucose tolerance (IGT) and of Type 2 diabetes mellitus (Type 2 DM) in siblings of patients with Type 2 DM, and to assess insulin release and insulin sensitivity in siblings with normal glucose tolerance (NGT), compared with NGT spouses of probands without family history of Type 2 DM. DESIGN AND METHODS: We evaluated 87 families including 103 Type 2 DM patients (87 probands), and we carried out an oral glucose tolerance test (OGTT) in 130 siblings and in 60 spouses. Among NGT subjects, 12 siblings and 16 spouses underwent a low-dose insulin-glucose infusion test (LDIGIT) to evaluate C-peptide release and insulin sensitivity. RESULTS: After the OGTT, 24 siblings were classified as having Type 2 DM, 31 as IGT, and only 14 spouses as IGT (P=0.0012 vs siblings). NGT siblings (n=75) showed higher insulin levels at 120 min than NGT spouses (n=46) at OGTT, in spite of identical blood glucose levels; at LDIGIT, NGT siblings secreted more C-peptide and showed a lower insulin sensitivity than NGT spouses. CONCLUSIONS: These data indicate that middle-aged siblings of probands with Type 2 DM have a high frequency of IGT and Type 2 DM, and that NGT siblings have increased insulin resistance and increased insulin secretion when compared with adequate controls.

OBJECTIVE: The purpose of this study was (a) to study whether a folate and vitamin B12 treatment, aimed at decreasing homocysteine levels, might ameliorate insulin resistance and endothelial dysfunction in patients with metabolic syndrome according to the National Cholesterol Education Program-Adult Treatment Panel-III criteria and (b) to evaluate whether, under these metabolic conditions, there is a relationship between hyperhomocysteinemia and insulin resistance. DESIGN AND METHODS: A double-blind, parallel, identical placebo-drug, randomized study was performed for 2 months in 50 patients. Patients were randomly allocated to two groups. In group 1, patients were treated with diet plus placebo for 2 months. In group 2, patients were treated with diet plus placebo for 1 month, followed by diet plus folic acid (5 mg/day) plus vitamin B12 (500 microg/day) for another month. RESULTS: In group 2, folate treatment significantly decreased homocysteine levels by 27.8% (12.2+/-1.2 vs 8.8+/-0.7 micromol/l; P<0.01). A significant decrement was observed for insulin levels (19.9+/-1.7 vs 14.8+/-1.6 microU/ml; P<0.01) accompanied by a 27% reduction in the homeostasis model assessment levels. A positive relationship was found between the decrement of homocysteine and insulin levels (r=0.60; P<0.002). In parallel, endothelial dysfunction significantly improved in the treated group, since post-ischemic maximal hyperemic vasodilation increased by 29.8% and cGMP by 13.6% while asymmetrical dimethylarginine levels decreased by 21.7%. On the contrary, in group 1 patients, treated with placebo, no changes were shown in any of the variables. CONCLUSIONS: Folate and vitamin B12 treatment improved insulin resistance and endothelial dysfunction, along with decreasing homocysteine levels, in patients with metabolic syndrome, suggesting that folic acid has several beneficial effects on cardiovascular disease risk factors.