The numbers are in, and the results are clear: Blood sugar control is key to preventing complications for people with Type 1 diabetes.

The University of Pittsburgh's Graduate School of Public Health tracked people with Type 1 diabetes for three decades to determine the causes of diabetes complications, which can involve kidney and eye damage, cardiovascular disease and circulation problems.

That study, combined with the national Diabetes Control and Complications Trial and the follow-up study known as the Epidemiology of Diabetes Interventions and Complications, produced clear recommendations for controlling Type 1 diabetes.

The common method of gauging diabetes control is an A1C test, which provides an average of blood-sugar levels over a period of months. Those with Type 1 who kept hemoglobin A1C levels close to the upper level of normal of 6 percent and generally below 7, on average, delayed and even avoided complications. Normal is 4 percent to 6 percent. Those with diabetes are encouraged to keep their A1C below 7 percent.

Research funded by the National Institutes of Health tracked 1,441 patients over 30 years, with the Pittsburgh Epidemiology of Diabetes Complications observational study following 161 Pittsburgh-area patients from 1983 through 2005.

Combined study results, published today in the Archives of Internal Medicine, concludes that the "frequencies of serious complications in patients with Type 1 diabetes, especially when treated intensively, are lower than that reported historically."

"These results should be used to motivate patients to implement intensive therapy as early as possible," the study concludes.

About 10 percent of diabetes cases involve Type 1, known as juvenile diabetes because it often develops in young people. Those with this condition produce little or no insulin, which regulates body sugars.

Dr. Trevor Orchard, interim chairman of the Pitt graduate school's Department of Epidemiology, said the study emphasizes the importance of bringing blood-sugar levels under control soon after diagnosis.

The study compared overall rates of eye, kidney and cardiovascular complications in three groups diagnosed with Type 1 diabetes an average of 30 years earlier. Two groups of participants randomly were assigned either to control glucose levels intensively or follow more traditional, less stringent methods of control. The third group involved Allegheny County residents diagnosed with Type 1 diabetes between 1950 and 1980.

Thirty years after being diagnosed with diabetes, 21 percent of participants assigned to intensive glucose control had eye damage, compared with 50 percent of the control group. Nine percent of the intensive-control group had kidney damage compared with 25 percent of the control group. And 9 percent of those undergoing intensive control suffered cardiovascular disease, compared with 14 percent in the control group.

Eye damage ranged from some vision loss to blindness. Kidney damage ranged from mild disease to renal failure. Cardiovascular events included heart attack, stroke, angina, and obstruction of the coronary arteries.

"I think the magnitude of the effect is pretty impressive in the halving of these rates of complications," Dr. Orchard said. "Because you are reducing blood-sugar levels early on, it is taking much, much longer for complications to develop.

"Sadly, we can't say that you can wipe out complications," he said. "It would be hard to maintain everyone at normal blood-sugar levels."

Controlling blood-glucose levels requires effort and physicians' guidance. Intensive maintenance requires glucose monitoring and countering high readings with insulin injections. Exercise and dietary control along with controlling blood-pressure and cholesterol levels also brings health advantages.

"Any lowering of blood sugar is helpful -- not that you have to get it down to a 6 percent A1C to have any benefits," Dr. Orchard said.

The study also found that health, disability and life insurance providers are using antiquated data to deny coverage to people with controlled Type 1 diabetes. People with controlled Type 1 have life expectancies longer than insurance tables might suggest.

Even those whose diabetes hasn't been closely controlled can realize benefits by gradually lowering glucose levels toward the normal range. Lowering levels too fast can cause problems.

Previous studies produced a formula to predict the onset of complications: Onset is likely when the number of percentage points above 6 percent A1C, multiplied by the number of months at that level, reach 1,000, Dr. Orchard said.

That means someone with an A1C of 10 -- 4 percent over the normal range -- could expect complications about 21 years after diagnosis. A child diagnosed at age 9 likely would experience complications at age 30. An average A1C of 11 will bring complications in about 17 years.

Intensive blood-sugar control is worth the effort.

"After 30 years of diabetes, fewer than 1 percent of those receiving intensive glucose control ... had significantly impaired vision, kidney failure, or needed a limb amputation due to diabetes," said Dr. Saul Genuth, the Case Western University researcher who co-chaired one of the earlier studies.

"Tight control is difficult to achieve and maintain, but its benefits have changed the course of diabetes."