Low-Normal Blood Sugar May Aid Memory

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Harvard Medical School
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Low-Normal Blood Sugar May Aid Memory

News Review From Harvard Medical School

October 24, 2013

News Review From Harvard Medical School -- Low-Normal Blood Sugar May Aid Memory

Blood sugar at the lower end of the normal range may be best for protecting the brain, a new study suggests. The study included 141 older adults. Their average age was 63. None of them had diabetes or pre-diabetes (blood sugar levels that are above normal but below diabetes levels). The study did not include anyone who was overweight or had more than 3.5 alcoholic drinks daily. It also excluded anyone who had been diagnosed with memory and thinking problems. Researchers gave everyone memory tests and measured their blood sugar. Everyone also received a brain MRI scan. Although everyone had blood sugar in the normal range, those with lower levels did better on the memory tests. They also tended to have a larger hippocampus than those with slightly higher blood sugar. This area of the brain plays a major role in memory.  The journal Neurology published the study. HealthDay News wrote about it October 23.


By Robert H. Shmerling, M.D.
Harvard Medical School


What Is the Doctor's Reaction?

When I was a kid, I heard a lot about low blood sugar, or hypoglycemia.

One of my classmates had it. My aunt had it. I wondered if I'd get it.

Yet, it came up rarely in medical school. The only time we talked about hypoglycemia in detail was when we were discussing the treatment of diabetes and the dangers of taking too much medicine. My schoolmate and aunt weren't diabetic. Why did they have hypoglycemia? 

They probably didn't. It turns out that the diagnosis was often given without actually measuring blood sugar. In fact, many people diagnosed the condition themselves, without seeing a doctor. If they felt jittery, light-headed or hungry, and felt better after eating, they assumed that their blood sugar was low. Eating frequent, small meals was the cure.

The diagnosis of unexplained hypoglycemia has fallen out of fashion and for good reason. Having a blood sugar low enough to cause symptoms is quite rare unless you are taking a diabetes medicine (such as insulin) that lowers your blood sugar more than intended.

But now a study is reporting that lower blood sugars may actually be helpful. Researchers found that blood sugar levels at the lower range of normal may be good for the brain. The journal Neurology published the study.

The study included 141 older adults with an average age of 63. Researchers compared their performance on memory tests with their blood sugar results. Each person also received an MRI scan of the brain.

The researchers found that, on average, those with lower blood sugar values had:

  • Higher scores on memory tests than those with higher results (even though all of the results were within a normal range)
  • A larger hippocampus, a part of the brain involved with memory

These findings do not prove that lower blood sugar leads to better memory. There could be other explanations for the results. For example, maybe those with lower blood sugar ate a better diet. This or other factors (rather than the lower blood sugar) could have led to better brain function.

This study excluded people who were overweight or who had diabetes or pre-diabetes (blood sugar that is slightly high but not high enough to diagnose diabetes). So we don't know if the results would have been the same in people with diabetes or those who are prone to it.

Still, these findings are intriguing. They raise the possibility that lowering your blood sugar -- even if it is normal -- might be a good idea.


What Changes Can I Make Now?

It's too soon to know whether the results of this study should lead to any new advice.  However, taking steps to lower your blood sugar may be worthwhile because it may have other health benefits. For example, here's what you can do to lower your blood sugar: 

  • Get regular exercise. Try to get at least 30 to 45 minutes of moderate-intensity exercise most days of the week.
  • Improve your diet. Choose lots of fruits, vegetables and whole-grain foods.  Avoid saturated and trans fats.
  • Limit your calories. Pay attention to portion size, as large portions are a major source of excess calories.
  • Avoid excess weight. Maintaining an ideal body weight is probably the most important way to avoid developing type 2 diabetes.

If you already have diabetes, work with your doctors to keep your blood sugar well controlled. This may prevent related health problems such as nerve disease, kidney failure and vision loss. It may also help you to maintain good brain function. Stroke and dementia may complicate poor blood sugar control among people with diabetes.


What Can I Expect Looking to the Future?

You can expect researchers to design studies answering questions raised by this new study.  For example:

  • Among people with normal blood sugar, why do some people have higher values than others?
  • For people with a normal blood sugar, would lowering it through diet, exercise or medicines lead to improved memory? Would it have other health benefits?
  • Would reducing blood-sugar levels improve brain function among people with established memory problems (such as those with Alzheimer's disease)?
  • If blood sugar levels in the lower range of normal are truly linked with better health, should the definition of normal blood sugar be changed?

Hypoglycemia is no longer the health threat I thought it was as a kid. But this new research could lead to an ever more dramatic change in our understanding. Lower blood sugar may actually be a sign of good health.

Last updated October 24, 2013

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