And tighter control is advisable for diabetics who don't have many accompanying medical conditions, Greenfield noted. "It should be tailored, and those people who most benefit from a low blood sugar level should strive for it," he said. "In persons where everything [else] is working, you should get below 7 if possible."
Several previous studies have shown little or no benefit, or even increased danger of heart disease, from too-tight control of blood glucose levels in type 2 diabetes, said Dr. David Nathan, a professor of medicine at Harvard Medical School and director of the Diabetes Center at Massachusetts General Hospital, who wrote an accompanying editorial.
One such study, reported earlier this year, found a 10 percent increased risk of death associated with intense efforts to reduce blood sugar levels in diabetics treated in hospital intensive care units.
But, Nathan noted, "we have lots and lots of data showing that keeping average blood sugar over the preceding three months at less than 7 percent is good for you. It is good in particular to protect the eyes, kidneys and nerves from the ravages of diabetes. The question is whether driving the level even lower will protect you further. There are several large studies showing that there is no benefit in terms of heart disease or even that it may be dangerous."
The new study is not definitive, since it is observational, without the controls that mark the best medical trials, Nathan pointed out. For a definitive controlled trial, "you would need to treat a younger, healthier population for a longer period of time to see a benefit," he said. The size and cost of such a trial make it highly unlikely that one will be done, Nathan added.
For people with type 2 diabetes, "7 percent should be the goal for most patients," he said. "Efforts to push the level much lower are currently not sup
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