Prediabetes — what your A1c means and what you can do about it.

YOUR HEALTH — Issue No. 28

I can usually tell before I order the lab.

A patient comes in for a routine visit. Their BMI is elevated. They are not particularly active. They eat the way most Americans eat. They have a parent with diabetes. They are somewhere between 45 and 65.

When the A1c comes back at 6.1% — prediabetes — they are surprised. The result was not entirely unexpected. What often surprises people is that they can feel perfectly well while their blood sugar is beginning to change.

Prediabetes is a meaningful health finding — and one of the most actionable diagnoses in primary care. Most people who have it have never been told what it actually means or what they can do about it.

What prediabetes actually is

Prediabetes is a health condition in which blood sugar is higher than normal but not yet in the range used to diagnose type 2 diabetes.

The numbers that define it:

A1c between 5.7% and 6.4% — the most commonly used screening measure in clinical practice. The A1c reflects your average blood sugar over approximately the past three months. Below 5.7% is normal. At or above 6.5% on two separate tests is generally the threshold for a diabetes diagnosis — though when there are no clear symptoms, an abnormal result typically needs confirmation with a repeat test. The range in between is prediabetes.

Fasting glucose between 100 and 125 mg/dL — blood sugar measured after at least eight hours without eating. Below 100 is normal. At or above 126 mg/dL on two separate tests is diabetes. The range in between is prediabetes.

Both tests can be used to identify prediabetes. In clinical practice, A1c is the most commonly ordered because it does not require fasting. But they do not always agree — a patient can have a normal fasting glucose and an elevated A1c, or vice versa. If your numbers are borderline on one test, asking your provider to check the other is reasonable.

Understanding insulin resistance — the concept that ties everything together

Before the risk factors and the interventions, one concept makes all of them easier to understand.

Insulin is the hormone responsible for moving glucose from the bloodstream into cells — particularly muscle cells — where it can be used for energy. When cells respond well to insulin, your body can manage blood sugar efficiently without needing large amounts of the hormone.

When insulin resistance develops, the body compensates by producing more insulin to keep blood sugar in range. For a while, this works. As insulin resistance increases, the pancreas responds by producing more insulin to compensate. For a while, this works. But even with elevated insulin levels, glucose clearance becomes less efficient — and blood sugar begins to rise.

Prediabetes is the period when blood sugar has risen above normal but has not yet reached the diabetic range. This is a useful time to act: insulin resistance can improve, and lifestyle changes can lower the chance of progressing to type 2 diabetes. The interventions in this issue work through this mechanism — each one addresses insulin resistance through a different pathway.

How common it is — and why most people don’t know they have it

Approximately 115 million American adults have prediabetes — more than 2 in 5 adults. Among adults 65 and older, the figure is about 52%.

8 in 10 people with prediabetes do not know they have it.

That number is not because prediabetes is hard to detect. It is because it produces no symptoms. Blood sugar in the prediabetic range does not cause fatigue, thirst, frequent urination, or any of the classic diabetes symptoms. You feel exactly the same at an A1c of 6.1% as you do at 5.5%. The difference exists entirely in the lab — which is precisely why routine screening matters and why waiting for symptoms is the wrong strategy.

Diabetes screening is recommended for adults beginning at age 35, with earlier testing for people with certain risk factors. If you have risk factors or have not had your blood sugar checked in several years, ask your healthcare provider whether screening is appropriate for you.

The clinical reality of who gets it

I have ordered a lot of A1cs that came back in the prediabetic range. In most cases — not all — the result was not a surprise to me even before the lab came back.

Prediabetes is strongly predicted by a cluster of risk factors that are visible in the exam room:

Elevated BMI — particularly abdominal adiposity. Visceral fat is closely linked to insulin resistance.

Physical inactivity — skeletal muscle is the primary site of glucose uptake in response to insulin. When muscle is not being used regularly, insulin resistance tends to increase.

Family history of type 2 diabetes — a first-degree relative with diabetes meaningfully increases lifetime risk.

Age — insulin resistance increases naturally with age. The prediabetes prevalence curve rises sharply after 45.

History of gestational diabetes — one of the stronger predictors of future metabolic risk in women.

High blood pressure and high triglycerides — both overlap significantly with insulin resistance and prediabetes.

None of these individually makes a diagnosis. But a patient with several of them who has never had their blood sugar checked is a patient whose A1c I want to know.

If you have several of these risk factors and have never been screened — the test is a routine blood draw. Ask for one.

What the evidence shows about progression — and reversal

Prediabetes means your blood sugar is higher than normal, but it does not mean you are destined to develop diabetes. It gives you a chance to understand what is happening and decide what steps make sense for you.

A 2025 analysis of 19 prospective cohort studies followed more than 76,000 people. Among those with fasting glucose in the prediabetes range, the estimated 10-year probability of returning to normal blood sugar was 36.1%, compared with 12.5% for progression to type 2 diabetes.

These are population-level estimates, not a prediction for any one person. But they offer a useful reminder: progression is not inevitable, and returning to normal blood sugar is possible.

What actually moves the number

The interventions with the strongest evidence share a common mechanism — reducing insulin resistance — and each works through the pathway described earlier in this issue.

Weight loss

5 to 7% of body weight is the target associated with meaningful improvement in the Diabetes Prevention Program. For a 200-pound adult, that is 10 to 14 pounds. Weight is not the only factor, and it is not the only path forward — but for people carrying excess body fat, it is one of the most direct ways to reduce insulin resistance.

Physical activity

150 minutes per week of moderate-intensity aerobic activity is the evidence-based target — 30 minutes five days a week of brisk walking, cycling, or anything that elevates heart rate to a moderate level.

Resistance training adds additional benefit — building muscle mass increases the body’s overall glucose disposal capacity. A combination of both is more effective than either alone.

Dietary pattern

No single diet is necessary for improving blood sugar. What the evidence consistently supports: reducing ultra-processed foods and added sugar, increasing dietary fiber to support steadier blood sugar, and adequate protein to support satiety and muscle mass. Mediterranean, DASH, lower-carbohydrate — multiple approaches work when they improve overall dietary quality.

Sleep

Chronically poor sleep impairs glucose regulation independently of diet and exercise. Treating sleep apnea, when present, is one of the highest-leverage interventions for metabolic health.

You do not need to overhaul your life this week. Start with one change you can repeat — a walk after dinner, a few sessions of strength training, replacing a sugary drink with water. Build from there.

When medication enters the conversation

Lifestyle change is the first-line intervention for prediabetes. Medication is not a failure. It is a tool.

Metformin works by reducing the amount of glucose the liver releases between meals and improving how efficiently muscle cells respond to insulin — directly lowering insulin resistance through a different pathway than exercise. It has evidence for preventing or delaying progression from prediabetes to type 2 diabetes, particularly in adults under 60, those with a BMI above 35, and women with a history of gestational diabetes.

The landmark Diabetes Prevention Program found that an intensive structured lifestyle intervention reduced the risk of developing diabetes by 58% compared with placebo over three years — and metformin reduced it by 31%. Lifestyle change outperformed medication. They work through different mechanisms, which is why the combination can be more effective than either alone.

Whether metformin makes sense alongside lifestyle change is a conversation worth having with your provider, particularly if your A1c is at the higher end of the prediabetic range or if lifestyle changes have not moved the number after a genuine effort.

If your A1c is between 5.7% and 6.4%, you have an opportunity to act on information you might not otherwise have had. Talk with your healthcare provider about your overall risk, choose one or two changes you feel ready to make, and decide when to recheck your numbers. Progress matters more than perfection.

Want the full clinical picture?

The paid deep-dive this week covers the clinical questions that often don’t fit into a routine visit: what your numbers mean when A1c and fasting glucose don’t agree, whether you can test insulin resistance directly and what the honest answer is, the questions worth asking your provider — including one most patients never think to say out loud — and how quickly prediabetes can actually improve when the right changes are made.

Next week: Type 2 diabetes — what a diagnosis actually means, how it is managed, and what the evidence shows about the medications that change long-term outcomes.

Plain Medicine is published for educational purposes only and does not constitute medical advice or establish a patient-provider relationship. Always consult your healthcare provider before making medical decisions.

— Kyle