Predictably, people with the highest blood sugar levels (over 10 percent) had a much greater chance of dying during the study. But so did those with the lowest levels (6.1 percent to 6.6 percent), despite the fact that their blood sugar was closest to the normal range. The people least likely to die during the study had levels ranging to 7.4 percent to 7.7 percent—notably above the usual recommended levels.

The researchers didn't gather data on the causes of death, so they weren't able to explore why people with lower blood sugar levels had a higher risk of dying. However, one plausible explanation is that people with lower levels were more likely to have had episodes of low blood sugar (hypoglycemia). If not treated, hypoglycemia can make you lose consciousness, go into a coma, and even die. Studies have also suggested hypoglycemia can trigger other serious problems, such as a change in heart rate (cardiac arrhythmia). (Also see car wreck risk for well-controlled diabetes.)

The researchers also found that people taking insulin had a 49 percent higher risk of dying than those taking pills to control their blood sugar. This might have been partly because people who use insulin for type 2 diabetes tend to be older and sicker. However, researchers still found similar results after factoring in people's age and whether they had been diagnosed with heart problems and other health issues at the start of the study. So something more appears to be at work here. One likely factor: studies show that insulin is more likely to cause hypoglycemia than pills that lower blood sugar.

What you need to know. So what does all this mean if you have type 2 diabetes? Unfortunately, there are no clear answers. This research lends support to another recent study, which was stopped early when researchers discovered a higher risk of death among people tightly controlling their blood sugar. However, other studies have found no such risk, and instead conclude that keeping blood sugar at near-normal levels is beneficial, protecting against serious diabetes risks, such as heart attacks and strokes.

The researchers acknowledge that more studies are needed. But they also suggest that it may be time to revisit treatment guidelines to set a minimum blood sugar level, perhaps around 7.5 percent.

But what about your own blood sugar goal? This is something you should decide with your doctor—and you may want to ask about this research as part of your discussion.

—Sophie Ramsey, patient editor, BMJ Group

ConsumerReportsHealth.org has partnered with The BMJ Group to monitor the latest medical research and assess the evidence to help you decide which news you should use.

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