DEAR DOCTOR K: In a recent column you said that doctors are not trying to lower blood sugar as much as they used to in people with diabetes. My husband’s doctor always tells him that “lower is better” when it comes to his blood sugar. Can you explain?
DEAR READER: When I was in medical school, and for many years thereafter, “lower is better” was what doctors believed. We knew that people with diabetes could develop severe, even fatal, complications if their blood sugar got very high. Plus, we had powerful blood-sugar-lowering treatments available.
On the other hand, there was a limit to “lower is better.” Too much of a good thing could be a bad thing: Overtreatment could push blood sugars too low – dangerously low. Sustained very low blood sugar can produce confusion, coma and death. So we measured blood sugars frequently, with the goal of having blood sugar as low as it could go without causing bothersome symptoms.
That was the goal because studies many years ago had shown that such “intensive treatment” reduced some types of complications of diabetes. Doctors speak of two types of complications of diabetes, both involving blood vessels. The first is disease of small blood vessels (called microvascular complications), which affects the eyes, kidneys and nerves. The second is disease of the large blood vessels (called macrovascular complications), which causes heart disease, strokes and peripheral artery disease.
An analysis of the strongest type of studies, randomized trials, involving nearly 35,000 people with diabetes, found that intensive treatment had a benefit: It led to a more than 10 percent reduction in small blood vessel complications.
I assumed, as did most doctors I know, that if intensive treatment lowered small blood vessel complications, then it would also lower large blood vessel complications. However, over the past 40 years, the evidence on that score has been quite mixed.
Many studies show that people with higher blood sugars are more likely to have large blood vessel complications, such as heart attacks and strokes. So you might think that intensive lowering of blood sugar would reduce the rates of large blood vessel complications. But that’s not necessarily true.
The way to see if it is true is through large, randomized trials. In these studies, some people with diabetes (chosen at random) were given intensive treatment that kept their blood sugars very low. Others were treated less intensively and had higher blood sugars. These studies all have abbreviated names. The best known are VADT, ACCORD and ADVANCE.
Unfortunately, these trials did not demonstrate a benefit from intensive treatment compared to less intensive treatment. And more patients in the intensive treatment group have suffered from the complications of blood sugar that is too low. Worst of all, in one of the studies (ACCORD), the rates of premature death from heart disease and from all causes were actually higher in the intensive treatment group. Too much of a good thing might have been fatal. One possible reason is that the low blood sugar may have triggered a dangerous heart rhythm.
So, while lowering blood sugar with treatment definitely improves health, there are limits. Today I and many other doctors do not treat blood sugar as intensively as we used to.
(Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.)
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