June 16, 2006 12:00 am
A method of intensive diabetes self-management that involves keeping blood glucose levels as close as possible to normal without causing severe or frequent episodes of hypoglycemia (low blood sugar), in the aim of preventing complications of diabetes. The term “tight control” has been around for decades, as researchers hotly debated whether aggressive blood glucose control could lower the risk of developing diabetic complications, including eye disease, kidney disease, and nerve disease. In recent years, a number of large clinical trials put the debate to rest. Based on the results of these trials, the American Diabetes Association (ADA) began to define tight control in terms of numeric values and urged most people with diabetes to strive for these more stringent goals. Even so, experts say that no single range of blood glucose levels works for everyone, and that these goals must be individualized.
In the Diabetes Control and Complications Trial (DCCT), which ended in 1993, 1,441 people with Type 1 diabetes were randomly assigned to receive either standard diabetes care or intensive insulin therapy. While the standard care group had one or two insulin injections per day, the intensive care group was treated with three or more daily insulin injections or insulin pump therapy, had frequent contact with health-care providers, and checked their blood glucose level four or more times a day. After an average of 6.5 years of therapy, the standard care group had an average glycosylated hemoglobin (HbA1c) level of about 9%, while the intensive care group achieved an HbA1c level of 7%. (The HbA1c level indicates a person’s average blood glucose level over the previous two to three months and is a good measure of how well blood glucose is being controlled. The average for people who don’t have diabetes is less than 6%.) More important, researchers found that the intensive care group had significantly lower rates of diabetic eye disease, diabetic kidney disease, and diabetic nerve disease. Years after the completion of the DCCT, the average HbA1c for all participants had leveled to around 8%, but those who had practiced tight control during the study continued to have fewer complications.
The results of follow-up studies, published in 2003 and 2005, showed that the DCCT participants who had practiced tight control also lowered their risk of atherosclerosis and heart disease.
An even larger clinical trial, the United Kingdom Prospective Diabetes Study (UKPDS), studied the effects of intensive blood glucose control in over 5,000 adults newly diagnosed with Type 2 diabetes. In this study, the standard care group was treated with lifestyle interventions alone (diet and exercise) unless symptoms of severe hyperglycemia (high blood glucose) developed and pharmacologic intervention became necessary. The intensive care group was treated with insulin, metformin, or a sulfonylurea drug such as glyburide (brand names Micronase, DiaBeta, Glynase), or a combination of these. At the end of the study, the standard care group had an average HbA1c of 7.9%, while the intensive care group had attained an HbA1c of 7%. Although this may not seem like a big difference, the intensive care group had a significantly lower rate of all complications of diabetes. In particular, for each 1% reduction in HbA1c level (for example, from 9% to 8%), there was a 35% reduction in the risk of developing microvascular (small-blood-vessel) complications like eye disease, kidney disease, and nerve disease.
Based on this and other powerful evidence, aggressive blood glucose control as practiced in the DCCT and UKPDS has become the goal of self-care for most people with diabetes, and they should expect their doctors to help them achieve tight control.
To reach the target HbA1c of less than 7%, the ADA recommends aiming for the following blood glucose levels:
If premeal blood sugar levels are consistently within the target range but the HbA1c level is still high, the ADA suggests monitoring one or two hours after meals and treating out-of-range numbers appropriately.
Ultimately, blood glucose targets must be tailored to the individual, and tight control is not for everyone. All of the studies demonstrating the value of tight blood glucose control have also shown that it is associated with an increased risk of hypoglycemia. Those who are especially prone to hypoglycemia may need somewhat higher target values. In particular, elderly adults, who can experience stroke or heart attack from episodes of hypoglycemia, and who may have a harder time recognizing symptoms of hypoglycemia, may be advised not to attempt tight control. Some people who already have severe complications (particularly end-stage kidney disease) may also be advised against tight control. Work with a health-care professional before starting a regimen of tight control.
Tight control has also been associated with weight gain, but such weight gain can be prevented or reversed. The weight gain associated with improved blood glucose control usually comes from absorbing calories that previously were eliminated in urine, overtreating hypoglycemia, and consuming more food after learning to match carbohydrate grams with insulin. Consuming fewer calories and learning to treat hypoglycemia without overtreating it can remedy the situation.
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