Diabetics who tightly control their blood sugar — even if only for the first decade after they are diagnosed — have lower risks of heart attack, death and other complications 10 or more years later, a large follow-up study has found.

The discovery of this "legacy effect" may put new emphasis on rigorous treatment when people first learn they have type 2 diabetes, the most common form and the type linked to obesity.

Results were published online yesterday by the New England Journal of Medicine and were being presented at the European Association for the Study of Diabetes meeting in Rome.

Diabetes affects more than 18 million Americans. Most have type 2, which occurs when the body makes too little insulin or cannot use what it does produce. Being overweight raises this risk.

Researchers led by Dr. Rury Holman at the University of Oxford in England originally studied 4,209 newly diagnosed diabetes patients assigned to manage their blood sugar either through standard diet restrictions or medicines. In the drug group, most took sulfonylurea, which prompts the pancreas to release more natural insulin into the bloodstream. Overweight diabetics took metformin, sold in the United States as Glucophage. Treatment lasted on average 10 years.

That study showed intensive blood sugar control lowered the risks of eye disease and kidney damage, but did not find any significant difference in heart attack risk except in the overweight group taking metformin. Those results led to guidelines recommending tight blood sugar control still in wide use today.

The follow-up study was on 3,277 participants who were tracked for an average of 10 more years.

Within one year of the original study ending, differences in blood sugar control between the groups disappeared.

Despite that, the sulfonylurea group had a 15 percent lower risk of heart attack and a 13 percent lower risk of death compared with the diet group.

The benefits were even greater among overweight diabetics on metformin, who had a 33 percent lower risk of heart attack and 27 percent reduced risk of death.

"It really stresses the importance of taking the long term-view of a chronic disease," said Dr. Judith Fradkin, who heads the diabetes division at the National Institute of Diabetes and Digestive and Kidney Diseases.