What prediabetes means, and what reverses it

Prediabetes is a blood-sugar range between normal and type 2 diabetes: an HbA1c (your average blood sugar over about 3 months) of 5.7 to 6.4%, or a fasting glucose (a morning blood draw after not eating) of 100 to 125 mg/dL. ¹ It rarely causes symptoms, which is why more than 8 in 10 people who have it don't know. ² By the time a number crosses that line, the process behind it, insulin resistance, has usually been building for years.

What is prediabetes?

Prediabetes means your blood sugar runs higher than normal but not high enough to be called type 2 diabetes (for how lab reference ranges draw these lines, start there). It is defined three ways, one per standard blood-sugar test, and being over the line on any single one of them counts. ¹

For what each number measures, see the marker pages: A1c is your 3-month average, while fasting glucose is a single morning snapshot, and the two can disagree. Your A1c also converts to an everyday number, your estimated average glucose, which is the roughly 123 mg/dL in the example below.

Why a normal glucose doesn't mean normal metabolism

Insulin is the hormone that moves sugar out of your blood and into your cells. In insulin resistance, those cells stop responding well, so the pancreas makes more insulin to force glucose down. For a while it works, and a glucose reading looks normal, because the extra insulin is holding it there.

That compensation buys years of normal-looking numbers. In the Whitehall II study, which followed 6,538 British civil servants, insulin sensitivity was already falling 3 to 6 years before diabetes was diagnosed, while fasting glucose stayed nearly flat until it rose steeply in about the final three years before diagnosis. ⁴

This is why fasting insulin can flag trouble earlier than glucose. It is not a diagnostic test, and there is no single standard reference range for it, but a high fasting insulin sitting under a normal glucose is a recognized early signal of a system working overtime.

What are the symptoms of prediabetes?

Usually none, and that absence is the whole problem. Prediabetes rarely produces any symptom at all. Blood sugar in the prediabetes range is not high enough to cause the thirst, fatigue, or blurred vision of full diabetes, so a blood test is the only way to catch it.

Is prediabetes serious?

Prediabetes is serious for where it leads, even though it does not feel like anything. Left alone, it raises the risk of type 2 diabetes, and it travels with higher cardiovascular risk, meaning heart disease and stroke. ⁶ It is not permanent, though: it is a risk state that can move back toward normal or forward to diabetes, which is the reason to act while the numbers are still movable.

How is prediabetes diagnosed?

Prediabetes is diagnosed from a blood test, most often an HbA1c or a fasting glucose, sometimes an oral glucose tolerance test (a 2-hour test where you drink a measured sugar load and your blood is checked afterward). Because a single borderline number can be off, it is worth confirming before you act on it, either by repeating the same test or by a second test agreeing. For a diabetes diagnosis, the ADA requires two abnormal results unless classic symptoms plus a very high random glucose make it unequivocal. ¹

The three tests overlap but do not flag an identical set of people. The A1c is the most convenient but the least sensitive, so it can read normal when an oral glucose tolerance test would catch trouble clearing a sugar load (called impaired glucose tolerance). ⁵

Here is where an example A1c lands against those same cutoffs.

Who should be screened, and how often

The ADA recommends screening adults for prediabetes and diabetes starting at age 35, and sooner for anyone with overweight or obesity plus a risk factor such as a family history of diabetes. If you already have prediabetes, the ADA recommends re-screening for diabetes at least once a year, because the number can drift either way. Both the A1c and fasting glucose are inexpensive and often already part of routine bloodwork; only the A1c can be drawn without fasting. ¹

Can prediabetes be reversed?

Often, yes. The clearest evidence is the Diabetes Prevention Program, a US trial of 3,234 adults with prediabetes. A structured lifestyle program, aiming for 7% body-weight loss plus 150 minutes of activity a week, cut progression to type 2 diabetes by 58% over about 2.8 years, compared with placebo. Metformin, a diabetes medication, cut it by 31% in the same trial. ³

Lifestyle changes and treatment with metformin both reduced the incidence of diabetes in persons at high risk. The lifestyle intervention was more effective than metformin.Diabetes Prevention Program Research Group, New England Journal of Medicine, 2002

Whether medication has any role in your case is a decision for you and a clinician. For prediabetes, the first-line step is lifestyle change, and in that trial it outperformed the drug.

What moves it

These are the levers behind the trial evidence; which ones fit your situation is a conversation with your clinician.

1. 1Lose about 7% of body weightThat was the DPP target and the single biggest lever. For a 200-pound person it is roughly 14 pounds, and even partial loss helps.
2. 2Move 150 minutes a weekThe DPP paired the weight goal with about 150 minutes of moderate activity weekly, such as a brisk 30-minute walk five days. Working muscle pulls in glucose without needing as much insulin.
3. 3Protect your sleepShort and broken sleep may worsen insulin resistance, the process under prediabetes, so steady nights of 7 or more hours support the same machinery that weight and activity do.

Prediabetes is the window where the numbers are still movable. Confirm the result, work the levers that have evidence behind them, and retest to watch it move. If you are not sure which blood-sugar test you were handed, start with the plain map of them.

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