Diabetes gets a lot of attention these days, and for good reason: it can lead to serious health complications such as heart attack, kidney failure, amputation, blindness, and early death. But its precursor, aptly named prediabetes, doesn't get nearly as much airtime, despite affecting three times as many people.
One in three American adults — an estimated 96 million people — has prediabetes, which is characterized by blood sugar levels that are higher than the normal range but don't quite reach diabetes status. But the vast majority of people don't know when they have it. And this is where the danger — and opportunity — lie, Harvard experts say.
"As with every chronic, prevalent disease, it's incredibly important to understand who's at particularly high risk of progressing from prediabetes to diabetes," says Dr. Giulio Romeo, associate medical director of the Adult Diabetes Section at Harvard-affiliated Joslin Diabetes Center.
Unlike diabetes, prediabetes is "largely silent" and typically doesn't produce blatant symptoms that might clue us in to its presence, Dr. Romeo says. But subtler signs often show up that shouldn't be ignored, offering a valuable window to curb blood sugar levels and halt progression.
"Anyone whose blood sugar falls into the prediabetes range is going in only one direction unless changes are made," says Emma Samuels Grinblatas, a registered dietitian and practice manager in the Comprehensive Weight Management Center at Harvard-affiliated Beth Israel Deaconess Medical Center. "Genetic and lifestyle factors both play a role in the development of diabetes. Whether we like it or not, our bodies will behave in certain ways. We don't get to play with our genes, but we do get to make changes in our eating behaviors and lifestyle choices."
Risk factors and clues
The same factors that play into diabetes development — overweight or obesity, inactivity, and family history — increase the risk of prediabetes. Paying attention to these, along with any persistent fatigue, should alert you that you may be in jeopardy, Dr. Romeo says.
Also notice if you're getting more infections—especially vaginal yeast infections. This can happen in women with prediabetes whose blood sugar spikes after meals — perhaps several times a day — but whose fasting glucose levels stay within normal limits (see "Three types of blood sugar tests"). "Their response to meals can't be categorized as normal," Dr. Romeo says.
After eating larger meals, some people with prediabetes also experience repeated urination or blurry vision. These signs, too, are related to temporarily surging blood sugar levels. They also happen to mirror full-blown diabetes symptoms, but on a smaller scale.
"While we like to classify things in buckets, the truth is that prediabetes and type 2 diabetes are often on a continuum — it's the same process across different stages," Dr. Romeo says. "Sometimes people are on the brink, so they notice certain signs even if they don't, by the book, have type 2 diabetes."
Three types of blood sugar tests
Screening for prediabetes and diabetes relies on tests that measure levels of glucose (sugar) in the blood. Get tested every two to three years if your prior results are normal and there are no changes in your risk factors, says Dr. Giulio Romeo, associate medical director of the Adult Diabetes Section at Joslin Diabetes Center.
This trio of tests can reveal blood sugar levels. Ask your doctor which one — or combination — makes sense for you.
Fasting blood glucose. You stop eating eight or more hours before the test, which shows how well your body is able to process blood sugar overnight. A fasting blood sugar level of 99 milligrams per deciliter (mg/dL) or lower is considered normal, 100 to 125 mg/dL indicates prediabetes, and 126 mg/dL or higher indicates diabetes.
A1c. This reflects your average blood sugar level over the past two or three months. An A1c measurement be-low 5.7% counts as normal, 5.7% to 6.4% indicates prediabetes, and 6.5% or higher indicates diabetes.
Glucose tolerance test. This test, done after an overnight fast, involves taking several blood samples before and after you drink a sugary liquid. For a blood sugar measurement taken two hours after drinking the liquid, a level of 140 mg/dL or lower is considered normal, 141 to 199 mg/dL indicates prediabetes, and 200 mg/dL or higher indicates diabetes. A variation of this test is used to diagnose diabetes during pregnancy.
Frequent movement crucial
Lifestyle changes are the cornerstone of measures to prevent prediabetes from progressing, Harvard experts say. A new study, published online Sept. 21, 2022, by BMJ, underscores this concept, suggesting that women who've had a temporary form of diabetes during pregnancy can lower their risk of later developing the disease by 90% by adhering to five key lifestyle factors: healthy weight, high-quality diet, regular physical activity, moderate alcohol consumption, and not smoking. The researchers based their conclusions on an analysis of 28 years of health and lifestyle data on 4,275 women who'd had pregnancy-related diabetes; of these, 924 later developed diabetes.
Frequent movement, in particular, is pivotal in staving off the problem. A new study published online Dec. 2, 2022, by The Journal of Clinical Endocrinology and Metabolism suggests that women who take more steps each day may have a lower risk of developing diabetes. Researchers analyzed diabetes rates along with data from wearable fitness devices from 5,677 people (75% women). Participants whose daily step counts averaged 10,700 at the study's start were 44% less likely to develop diabetes over the following four years compared with those who averaged only 6,000 steps per day.
"Regular exercise plays a profound role on blood sugar," Grinblatas says. "The recommendation of 30 minutes of exercise at least five days a week can be broken down into 10-minute increments and include things like walking, yard work, and dancing. Any form of exercise is good for our bodies and brains."
And exercise pays off well beyond a shrinking waistline for people at risk of diabetes. "Exercise alone often won't result in weight loss," Dr. Romeo says, "but it has significant benefits that can't be measured by the scale — not just in terms of preventing progression to diabetes, but on your heart, mood, and many aspects of overall health not captured by a change in your weight."
Along with lifestyle changes, the drug metformin can boost diabetes prevention efforts for some people with obesity. Metformin lowers blood sugar levels by improving the way the body shuttles sugar from the blood into the cells of muscles and other tissues, where it's used as fuel. Research shows metformin reduces the odds prediabetes will progress to diabetes by about one-third, Dr. Romeo says, though lifestyle interventions work even better — lowering the chance of progression by about 60%.
"For some, maybe the focus is not about losing weight, but how you should exercise at whatever level you can — looking at this not as a sprint but as something you can incorporate into your routine over the years," he says.
Diet and diabetes: It's complicated
Some people believe eating desserts — or foods containing processed sugar — can give them diabetes. But it's not that simple, says Emma Samuels Grinblatas, a registered dietitian at Beth Israel Deaconess Medical Center.
Type 2 diabetes results from a combination of two processes. First, the body becomes resistant to the hormone insulin and can't use it properly to carry glucose (sugar) from the blood into cells. In turn, the pancreas can't keep up with producing more and more insulin. But someone without diabetes who eats a few cookies or a piece of cake shouldn't have a problem, because her pancreas is working normally and can handle the task.
Grinblatas says many of her patients with diabetes have been "made to believe sugar is something they cannot have. But that's not the case," she says. "Nothing is inherently bad. It's all about balance."
Indeed, glucose is an energy source our body needs. While you should check food labels for sugar content, Grinblatas says it's just as important to monitor carbohydrate consumption — which can also cause blood glucose to rise — if you're concerned about diabetes.
A new study suggests that a low-carbohydrate diet may quickly bring elevated A1c levels (a measure of blood sugar over the prior several months) back to a healthier range. Published online Oct. 26, 2022, by JAMA Network Open, the study analyzed 150 older adults (75% women) with untreated prediabetes or less-severe diabetes over six months, randomly assigning half to a low-carb diet and frequent dietary counseling and the rest to their usual diet.
"Many of my patients work hard to reduce their sugar intake but still have a very high carb load," she says. "If you're having a bagel or breakfast bar in the morning, try having an egg, unsweetened yogurt, or old-fashioned oatmeal and put in some fruit or chopped nuts. A nice balance of carbs, healthy fats, and protein slows down digestion and helps people feel full."
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