The purpose of this report is to summarize and integrate the findings
of the Diabetes Control and Complications Trial (DCCT), a randomized controlled
clinical trial, and the succeeding observational follow-up of the DCCT cohort
in the Epidemiology of Diabetes Interventions and Complications (EDIC) study,
regarding the effects of intensive treatment on the microvascular complications
of type 1 diabetes mellitus. The DCCT proved that intensive treatment reduced
the risks of retinopathy, nephropathy, and neuropathy by 35% to 90% compared
with conventional treatment. The absolute risks of retinopathy and nephropathy
were proportional to the mean glycosylated hemoglobin (HbA1c) level
over the follow-up period preceding each event. Intensive treatment was most
effective when begun early, before complications were detectable. These risk
reductions, achieved at a median HbA1c level difference of 9.1%
for conventional treatment vs 7.3% for intensive treatment have been maintained
through 7 years of EDIC, even though the difference in mean HbA1c
levels of the 2 former randomized treatment groups was only 0.4% at 1 year
(P<.001) (8.3% in the former conventional treatment
group vs 7.9% in the former intensive treatment group), continued to narrow,
and became statistically nonsignificant by 5 years (8.1% vs 8.2%, P = .09). The further rate of progression of complications from their
levels at the end of the DCCT remains less in the former intensive treatment
group. Thus, the benefits of 6.5 years of intensive treatment extend well
beyond the period of its most intensive implementation. Intensive treatment
should be started as soon as is safely possible after the onset of type 1
diabetes mellitus and maintained thereafter, aiming for a practicable target
HbA1c level of 7.0% or less.