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Blood Glucose Control Studies for Type 1 Diabetes: DCCT and EDIC

The NIDDK funded the landmark Diabetes Control and Complications Trial (DCCT) to see if people with type 1 diabetes who kept their blood glucose levels as close to normal as safely possible with intensive diabetes treatment (3 or more shots of insulin per day or an insulin pump with self-monitoring of blood glucose at least 4 times per day) could slow the development of eye, kidney, and nerve disease, compared to people who used the conventional treatment at the time of the study (one or two shots of insulin per day with daily self-monitoring of urine or blood glucose). The DCCT ended after 10 years in 1993—a year earlier than planned—when the study proved that participants who kept their blood glucose levels close to normal greatly lowered their chances of having eye, kidney, and nerve disease.

A follow-up to the DCCT, the ongoing Epidemiology of Diabetes Interventions and Complications (EDIC) study, has continued to follow DCCT participants for the last 20-plus years. EDIC has shown that there are long-term benefits of early and intensive blood glucose control on the future development of diabetes-related complications such as heart, eye, kidney, and nerve disease, and that early and intensive blood glucose control also lengthens life. Recently, EDIC has also shown that an individualized eye exam schedule results in fewer eye exams, resulting in lower costs, and quicker diagnosis and treatment of advanced diabetic eye disease.

Findings from DCCT/EDIC have changed the way diabetes is treated worldwide. As a result of DCCT/EDIC, early and intensive blood glucose control is now the standard treatment for people with type 1 and even type 2 diabetes, and helps people with diabetes live longer and healthier lives.

Diabetes Control and Complications Trial (DCCT)

DCCT Results

The DCCT showed that people with type 1 diabetes who kept their blood glucose levels as close to normal as safely possible with intensive diabetes treatment as early as possible in their disease had fewer diabetes-related health problems after 6.5 years, compared to people who used the conventional treatment.

DCCT showed that people who used intensive treatment lowered their risk of

  • diabetic eye disease by 76 percent; and advancement of eye disease by about half (54 percent), in people with some eye disease at the beginning of the study.
  • diabetic kidney disease by 50 percent.
  • diabetic nerve disease by 60 percent.

Researchers were not able to show whether people who used intensive treatment lowered their risk of heart disease during the DCCT, since only a few people had heart disease during the study.

Participants who used intensive treatment had an average A1C of 7 percent, while participants who used the conventional treatment had an average A1C of 9 percent. The A1C blood test shows a person’s average blood glucose levels over the previous 2 to 3 months. A normal A1C value is 6 percent or less.

In the DCCT, the major side effect of intensive treatment was a higher risk for hypoglycemia, also called low blood glucose, which can be deadly if not treated immediately. Participants knew how to treat hypoglycemia.

DCCT Study Size, Participant Demographics, and Study Design

The DCCT took place from 1983 to 1993. The study involved 1,441 volunteers ages 13 to 39, and took place in 29 medical centers in the United States and Canada. At the start of the DCCT, participants had type 1 diabetes for at least 1 year but no longer than 15 years, and had no or only early signs of diabetic eye or kidney diseases.

DCCT participants were randomly assigned to one of the following groups:

  • Intensive diabetes treatment group. Participants took insulin 3 or more times per day by injection or an insulin pump and self-monitored their blood glucose levels four or more times a day. The treatment goal was to keep A1C levels as close to normal as safely possible. Participants met with their health care team monthly.
  • Conventional diabetes treatment group. Participants used what was conventional diabetes treatment at the time (in the early 1980s): one or two shots of insulin a day with daily urine or blood glucose testing. Participants met with their health care team every 3 months.

Researchers followed participants for an average of 6.5 years and compared the study groups to see if there was more eye, kidney, and nerve disease in one group or the other.

After DCCT ended participants who used conventional treatment were taught about intensive treatment. Participants who continued into the EDIC follow-up study were transferred to their own health care team for medical care and were able to choose between conventional treatment or intensive treatment.

Epidemiology of Diabetes Interventions and Complications (EDIC) Study

EDIC Results

EDIC researchers are trying to understand how diabetes affects the body over time, and the long-term benefits of a period of early and intensive blood glucose control in the development of later complications from diabetes. EDIC has shown that early and intensive blood glucose control during the DCCT lowers the risk of

  • cardiovascular diseases (such as heart attack and stroke) and cardiovascular-related deaths by 57 percent, 11 years after the DCCT ended and 32 percent, 20 years after the DCCT ended.
  • eye surgery for diabetic eye disease by 48 percent, 17 years after the DCCT ended.
  • kidney disease and failure by 50 percent, 18 years after the DCCT ended.
  • nerve problems by about 30 percent, 14 years after the DCCT ended.

DCCT participants who had tight control of their blood glucose levels also lived longer. Historically, people with type 1 diabetes tended to die earlier than the general population. DCCT/EDIC researchers have found that this earlier death can be reduced or eliminated through careful management of blood glucose.

EDIC has shown that adjusting the frequency of eye screenings for people with type 1 diabetes based on their risk of severe eye problems and A1C level would result in

  • fewer eye exams by 50 percent, lowering the overall cost of care by 1 billion dollars over 20 years.
  • quicker diagnosis and treatment of advanced diabetic eye disease, a condition which can lead to vision loss.

These long-term benefits occurred even though all participants had an average A1C of 8 percent during the 20-plus years of the EDIC study. Participants from the DCCT’s intensive treatment and conventional treatment groups had similar blood glucose levels starting about 5 years after EDIC began.

EDIC Study Size, Participant Demographics, and Study Design

The EDIC follow-up study started in 1994, enrolling 96 percent of the living DCCT participants at the beginning of the study. When EDIC began, participants who used conventional treatment were taught about intensive treatment, and received follow-up care from their own health care team. The EDIC study is ongoing and includes the majority of the original surviving DCCT participants. These people continue to take part in studies of a variety of diabetes-related health problems, including hypoglycemia, irregular heartbeats, hearing loss, weakened bones, trouble thinking clearly, and problems with the eyes, kidneys, nerves, feet, bladder, and sexual function. Another study is looking at the small amount of insulin that some people with type 1 diabetes continue to make and whether this improves health.

Related Health Information

Related Studies

  • United Kingdom Prospective Diabetes Study - Researchers showed that controlling blood glucose levels in people with type 2 diabetes reduced the risk of diabetic eye disease and diabetic kidney disease.
  • Action to Control Cardiovascular Risk in Diabetes (ACCORD) Study - Researchers compared standard practice guidelines with more intensive blood glucose and blood pressure management and control of abnormal blood fats in 10,000 people with type 2 diabetes, including those at especially high risk for cardiovascular disease. ACCORD researchers found that participants maintained good control of blood glucose levels during the study, however the risk of cardiovascular events such as heart attack, stroke, and death was not lowered with intensive control of blood pressure or treatment for abnormal blood fats.

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