Updated January 31, 2008

The Benefits of Tight Control
No End in Sight

by Wayne Clark

It has been 14 years since the results of the landmark Diabetes Control and Complications Trial (DCCT) were published. Despite its continuing legacy of proof that maintaining blood glucose levels as close to normal as possible reduces the risk of diabetes complications, today less than half of people with diabetes are reaching target blood glucose levels, according to most estimates. Health-care providers and researchers continue to struggle with how to improve those numbers.

Recalling the DCCT
Researchers began recruiting participants for the DCCT in 1983. They signed up 1,441 people with Type 1 diabetes, roughly half within five years of their diagnoses and the rest within 15 years of diagnosis. The subjects were randomly assigned to either conventional insulin treatment or intensive treatment. Those on intensive treatment took three or more insulin injections each day or used an insulin pump and monitored their blood glucose levels three or four times a day. The goal for the intensive treatment group was to keep their glycosolated hemoglobin, or HbA1c levels (a measure of blood glucose control over two to three months) at or below the top of the normal range: 6.05%. In actuality they achieved a median HbA1c of 7.2%. The study’s subjects were followed for six and a half years, and the publication of the results in late 1993 changed the standards of Type 1 diabetes management forever.

The research team had hoped to be able to demonstrate a 30% to 40% reduction in complications among those on intensive treatment. What they actually saw was so significant that they ended the study early and advised the subjects on conventional treatment to switch to intensive treatment.

Those who were within five years of diagnosis and had been assigned to intensive treatment experienced a 76% reduction in the risk of diabetic retinopathy, or eye disease, a 34% reduction in the risk of microalbuminuria (an early stage of diabetic nephropathy, or kidney disease), and a 69% reduction in the risk of diabetic neuropathy, or nerve disease. Results for those within 15 years of diagnosis and on intensive treatment were less dramatic but still significant: a risk reduction of 54% for retinopathy, 43% for microalbuminuria, and 57% for neuropathy. In both groups there was a 41% reduction in the risk of cardiovascular disease.

The drawbacks for the intensive treatment group were a three-times higher incidence of severe hypoglycemia (very low blood glucose levels), and an average weight gain of 4.6 kilograms (about 10 pounds).

The study also answered the question of whether or not there is a point below which a lower HbA1c does not yield additional benefit. The answer was that there is no “glycemic threshold”: The closer to normal the better.

The DCCT ended in 1993, but more than 1,370 of its subjects were then enrolled in a long-term follow-up study called Epidemiology of Diabetes Interventions and Complications (EDIC). The news from EDIC in the past few years has been almost too good to be true: The benefit of intensive blood glucose management continues even after treatment becomes less monitored and less rigorous.

Wayne Clark is a freelance medical and science writer who has written extensively on diabetes. He lives in Maine.

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