Abstract
The Diabetes Control and Complications Trial (DCCT, 1983-1993) showed that intensive therapy (mean HbA(1c) 7.2%) compared with conventional therapy (mean HbA(1c) 9.0%) markedly reduced the risks of retinopathy, nephropathy, and neuropathy, and these reductions in complications were entirely attributable, statistically, to the difference in mean HbA(1c) levels. The DCCT cohort has been followed in the Epidemiology of Diabetes Interventions and Complications (EDIC) study (1994 to date). Early in EDIC, mean HbA(1c) levels in the former intensively and conventionally treated groups converged. Nevertheless, the beneficial effects of DCCT intensive versus conventional therapy on microvascular complications not only persisted but increased during EDIC. The differences in complications during EDIC were wholly explained, statistically, by differences between groups in HbA(1c) levels during DCCT. These observations give rise to the concept of metabolic memory. Subsequent similar findings from the UKPDS gave rise to a similar concept, which they called the legacy effect. In this report, we present the evidence to support metabolic memory as both a biological and epidemiological phenomenon and discuss potential underlying mechanisms. We also compare metabolic memory and the legacy effect and conclude that the two are likely biologically similar, with comparable effects on long-term outcomes. The long-term influence of metabolic memory on the risk of micro- and macrovascular complications supports the implementation of intensive therapy, with the goal of maintaining near-normal levels of glycemia, as early and as long as safely possible in order to limit the risk of complications.