How to Tell When Normal Blood Sugar Isn’t

Your tests might say you're safe, but new research claims that even normal-range results could mean trouble.

cup of sugar
Claire Benoist for Reader’s Digest

Most people don’t worry about diabetes until a doctor tells them their blood sugar is too high. But even if you get a “normal” blood sugar reading at your next exam, you might not be totally in the clear. According to cutting-edge research, blood sugar levels on the high end of the normal range may still raise your risk of illness, leading some doctors to take such results more seriously — particularly if patients have other diabetes risk factors, such as obesity or family history.

The somewhat arbitrary cutoff between normal blood sugar levels and higher ones associated with diabetes may give a false sense of security to millions of people, notes brain researcher Nicolas Cherbuin of Australian National University. His research published in 2013 found that middle-aged people with high-normal fasting blood sugar readings had worse scores on memory tests and more shrinkage in a brain region important to memory than those with lower blood sugar. Higher glucose levels may damage blood vessels and hinder the flow of nutrients to the brain.


• DIABETES: Blood sugar level of 126 mg/dl or higher

• PREDIABETES: Blood sugar level between 100 and 125 mg/dl

• HIGH-NORMAL BLOOD SUGAR: Roughly 90 to 99 mg/dl (a new category being studied for health risks)

• NORMAL BLOOD SUGAR: Currently defined as 70 to 99 mg/dl

* All levels are based on a fasting blood glucose test, which involves an overnight fast.

Other research suggests high-normal blood sugar may increase your heart disease risk by raising inflammation and making blood vessels stiffer. A 2012 Israeli study found that people with a fasting blood sugar between 90 and 99 mg/dl were 40 percent more likely to suffer heart disease than those with a level under 80 mg/dl.

Cancer is another concern. When researchers tracked Italian women for 13 years, those with high-normal fasting blood sugar were 52 percent more likely to develop breast cancer than those with a fasting glucose level below 80. One reason may be that the insulin the body pumps out to deal with blood sugar also speeds cell growth.

All adults should be aware of their blood sugar status and make lifestyle changes when their numbers sneak into the 90s, says preventive cardiologist Joel K. Kahn, MD, who treats many patients who have diabetes or are on the road to developing the disease.

“An ideal healthy fasting blood sugar is less than 85,” he says. “Every few points higher than that is associated with more problems, so the best approach is to take action early.”

The American Diabetes Association recommends blood sugar screening every three years starting at age 45, but you may need earlier or more frequent tests if you are from a high-risk ethnic group (African American, Native American, Pacific Islander, or Hispanic), if you are overweight, if you had gestational diabetes during pregnancy, or if you have close family members with diabetes, says Gail Nunlee-Bland, MD, director of the Diabetes Treatment Center at Howard University Hospital in Washington, DC.

Experts urge greater vigilance because important research shows that increased activity and a better diet can reverse the path to diabetes. A game-changing, 27-center study, the Diabetes Prevention Program found that people with prediabetes can reduce their risk of developing diabetes by 58 percent and sometimes even return blood sugar to normal levels if they exercise at least 150 minutes a week and lose a modest amount of weight, if needed (about 20 percent of those with prediabetes are slim).

The research found that lifestyle changes had even greater power than a diabetes medication, says Jill Crandall, MD, director of the Diabetes Clinical Trials Unit at the Albert Einstein College of Medicine in New York City. And the benefits can endure, according to results published in April from a similar study in China: After 23 years, those who participated in a long-term diet and/or exercise program were less likely to have developed diabetes or to have died from any cause.

If your blood sugar number is going higher, these science-backed diet, exercise, and wellness tips can help you get back to a healthier level.

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