The study, presented Sunday at the American Diabetes Association conference here, and two other major trials give the USA's estimated 20.8 million diabetics some answers and many more questions about how their disease should be treated.

Researchers presented preliminary data from the VA Diabetes Trial just eight days after it ended.

Another surprise from the VA study was that rosiglitazone, a controversial diabetes drug sold by GlaxoSmithKline as Avandia, was not associated with heart attacks and heart problems. Research published last year had found the popular drug to be associated with such problems.

Diabetics can fall victim to hypoglycemia when they don't eat enough, take too much medication or drink alcohol. The VA patients who suffered bouts of hypoglycemia had such low blood sugar levels that they either became mentally impaired or lost consciousness.

Preliminary findings were that patients who had become severely hypoglycemic in the previous three months were two or three times more likely to suffer a heart attack, stroke or death, says William Duckworth, co-chair of the study and director of research at the VA Medical Center in Phoenix.

What the VA study didn't find, along with the two other major studies presented, was that tightly controlling blood sugars had any positive effect on rates of heart attack or stroke in diabetics. All had been launched to look for such a link. Cardiovascular disease kills 75% of diabetics.

There were differences, however. The ACCORD study made news in February because it found that very tightly controlled blood sugar levels were linked to a higher death rate, though why is still unknown.

It could be that patients' glucose levels got too low or that the medicines used to lower them were toxic, says David Nathan, director of the Diabetes Center at Massachusetts General Hospital in Boston.

The other study, ADVANCE, found no link but did show a 21% drop in risk in kidney disease in tightly controlled patients.

The overarching message of the studies is that lowering average blood glucose levels is good for diabetics' eyes, kidneys and nerves — all subject to damage by the disease. But none of them showed that very tight glucose control helps heart disease in type 2 diabetics, Nathan says.

The VA's Duckworth adds that avoiding severely low blood sugar and early, aggressive treatment are key in avoiding complications.