Change in glucose intolerance status and risk of incident cardiovascular disease: Tehran Lipid and Glucose Study

To assess the impact of changes in different glucose tolerance states on risk of incident cardiovascular disease (CVD)/coronary heart disease (CHD).

A total of 4094 Iranians (43.9% men) aged ≥ 30 years, without diabetes and CVD at enrolment were included. The following categories were defined both at baseline visit and 3 years later (second visit): normal fasting glucose (NFG), normal glucose tolerance (NGT), NFG and NGT (NFG/NGT), impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and IFG and/or IGT (IFG/IGT). Changes in the categories, i.e. regression to normoglycemia, remaining in previous status and progression to diabetes were assessed. We used Cox's proportional hazard models adjusted for traditional risk factors and their changes, to estimate the hazard ratio (HR) with 95% confidence interval (CI) of different changing categories for incident CVD/CHD.

During a median follow-up of 12.42 years, 428 subjects (men = 265) experienced CVD. Considering persistent NFG/NGT as reference, participants who shifted from NFG/NGT to IFG/IGT showed a lower hazard of CVD in the fully adjusted model, HR 0.72 [95% CI 0.52-0.996, P = 0.048]. Moreover, subjects who shifted from IFG, IGT and IFG/IGT to diabetes had an increased risk of CVD/CHD. The risk however, was only statistically significant for those with IFG/IGT, 1.61 [(1.03-2.51), P = 0.04] for CVD and 1.75 [(1.10-2.78), P = 0.02] for CHD; considering IFG/IGT at both visits as reference. Furthermore, those who regressed from IFG/IGT to normoglycemia were at the same risk as those remained in IFG/IGT state, 1.12 [(0.79-1.60), P = 0.52] for CVD and 1.04 [(0.70-1.53), P = 0.85] for CHD. Among a subgroup of population with insulin data (n = 803) those with insulin resistance (IR) that converted to diabetes showed a higher risk for CVD, 3.68 [(1.49-9.06), P = 0.01] and CHD, 2.76 [(1.00-7.60), P = 0.05] events in the fully adjusted model.

Among participants with IFG, IGT or IFG/IGT at baseline, only those who developed diabetes had a higher risk of developing CVD/CHD. Persistent IFG/IGT was not associated with higher risk, compared with those reverted to normoglycemia. Moreover, subjects who converted from NFG/NGT to incident IFG/IGT showed a signal for lower risk of CVD/CHD.