The Blood Sugar Guide
More than 2 in 5 American adults have prediabetes, and 8 in 10 of them don't know it. Here's what your numbers mean, how to bring them down and how to track them.
Updated November 15, 2026. 29 guide pages, 31 questions, 9 myths, from 142 published sources.
100A fasting 100 mg/dL or an A1c of 5.7% is already the prediabetes range.
58%fewer new cases of diabetes with weight loss and walking, in the biggest trial.
10 minof walking after each meal beat one long walk a day.
140Healthy people's sensors go over it every day. A sensor runs higher than your blood.
Is my blood sugar normal?
8 hours or more with no food or calories, water only.
96 mg/dL is 5.3 mmol/L
NormalPrediabetes rangeDiabetes range
- The next line
- 4 points under the prediabetes line
- Can this test decide it?
- A lab test can decide a band. A diagnosis takes two results unless the number is clearly high.
Next step. Nothing to do. Test again every 3 years from age 35, sooner if your weight goes up.
All the sugar in your blood right now is about 4 grams, one teaspoon, in a 154 pound adult. A can of cola has almost 10.
The questions people ask
Your numbers
Does normal blood sugar change with age?The cutoffs don't. Averages creep up, 98 on healthy sensors under 60 and 104 over 60, and A1c rises about 0.1 a decade. Don't excuse a high number as age.
How long should you fast before a blood sugar test?At least 8 hours with no calories, so water only. Milk or sugar in coffee breaks the fast. If the number surprises you, repeat it on another morning.
How often should you get your blood sugar tested?Every 3 years from 35, starting earlier with extra weight and a risk factor, and every year once you have prediabetes. A home meter doesn't replace the lab.- Is a fasting blood sugar of 100 bad?It's the first number of the prediabetes range (5.6 mmol/L). One morning isn't a diagnosis. Get a lab fasting test and an A1c, and treat it as an early warning.
- Is a fasting blood sugar of 110 normal?No. 110 (6.1 mmol/L) is inside the prediabetes range of 100 to 125. Repeat it at a lab with an A1c. Caught here, it often goes back to normal.
What is a normal blood sugar level?Under 100 mg/dL fasting, under 140 two hours after a glucose drink, and an A1c under 5.7%. Those lines are the same at every adult age.
Why is my blood sugar high in the morning?Your liver releases glucose before you wake, in everyone. It's a problem only if a lab fasting test comes back at 100 or more.
A1c
- How long does it take to lower your A1c?About 3 months to see most of a change, since A1c weighs the last 100 days and the latest weeks most. A retest at 4 weeks mostly shows your old habits.
- What does an A1c of 5.7 mean?It's the first number of the prediabetes range, an average near 117 mg/dL (39 mmol/mol). Change your habits now and retest in about 3 months.
What is a normal A1c?Under 5.7%. 5.7 to 6.4% is the prediabetes range and 6.5% or more on two tests is diabetes. Anemia can throw it off, so pair it with a fasting test.
Why is my A1c high but my fasting sugar normal?They measure different things. Fasting is one morning, A1c is about 3 months of red cells, after-meal highs included, and red cell age shifts it too. Repeat both.
Why is my GMI different from my A1c?GMI turns a sensor's average into an A1c-like number with a formula. Sensors run high, so a healthy 98 mg/dL average gives a GMI of 5.7. Trust the lab A1c.
After meals
Does coffee raise blood sugar?In short trials, caffeine made people less sensitive to insulin for a while. Long term, each daily cup went with 9% less type 2 diabetes. Watch the syrup, not the coffee.- Is 140 high after eating?Two hours after the lab's glucose drink, 140 is the line. A sensor peak of 140 within an hour of a meal is ordinary. Healthy people spend about 30 minutes a day above it.
What is the best breakfast for blood sugar?Start with protein, like eggs or Greek yogurt, and pick rolled oats over instant (GI 55 against 79). Cornflakes sit near the top of the table at 81.
What should blood sugar be 2 hours after eating?Under 140 mg/dL (7.8 mmol/L). That line comes from the lab's glucose drink, so a home meal is a rough check. A clear 200 or more needs a doctor.
Why does blood sugar go up when you exercise?In hard efforts your liver releases glucose 7 to 8 times faster while muscles use 3 to 4 times more, so it rises, then settles. That's normal.
Lowering it
Can prediabetes be reversed?Often, yes. About as many people go back to normal each year as move on, and those who got back to normal even once had 56% lower diabetes risk later.
Does alcohol raise or lower blood sugar?Alcohol can cause low blood sugar, most of all with insulin or a sulfonylurea. In 67 men drinking 30 g of alcohol a day for 4 weeks, fasting sugar didn't change.
Does apple cider vinegar lower blood sugar?A little. In pooled trials, vinegar with a meal shrank the after-meal rise, but the effect was small and varied. A 10-minute walk has the stronger evidence.
Does eating carbs last lower blood sugar?Yes. Protein and vegetables first, carbs 10 minutes later, cut the peak by more than 40% in 15 people with prediabetes. Same food, different order.
Does poor sleep raise blood sugar?Yes, the next day. A week of 5-hour nights made healthy men 11% less sensitive to insulin, and one 4-hour night did it too. Protect sleep before buying supplements.- Does walking after eating lower blood sugar?Yes. Ten minutes after each meal beat one 30-minute walk a day by 12%, and by 22% after dinner. Go soon after eating. Short walks still beat sitting.
How do I lower my A1c naturally?Lose 5 to 7% of your weight if you carry extra, walk 150 minutes a week with 10 minutes after meals, and retest in 3 months. That plan cut new diabetes 58%.
Sensors
How accurate are glucose sensors?Good for shapes, loose for single numbers. In healthy adults one ran about 16 mg/dL above fingertip blood, and it measures fluid 5 to 6 minutes behind your blood.- Should you wear a glucose sensor if you don't have diabetes?For two weeks, to learn which of your own meals make big hills, it can help. Get a lab A1c first. No trial shows wearing one improves health without diabetes.
What is a normal time in range without diabetes?Far above the 70% on your report, which is a diabetes goal. Healthy people spent 87 to 96% of the day between 70 and 140. Compare your days with each other.
When to worry
- What are the early signs of prediabetes?Usually none, which is why 8 in 10 people with it don't know. The real early signs are your risk factors and a lab number: fasting 100 or more, or an A1c of 5.7% or more.
- What are the signs of high blood sugar?Thirst, peeing a lot, blurry vision, tiredness and weight loss you didn't try for. Prediabetes usually has none of these, which is why 8 in 10 don't know they have it.
- What blood sugar level is dangerous?Under 70 with shakiness needs fast sugar now, and under 54 is serious. Confusion, or staying at 300 or more with vomiting or hard breathing, means 911 or the ER.
Myth or fact?
Not the way you think Is every blood sugar spike bad for you?
Not the way you think Does eating sugar cause diabetes?
No Is fruit bad for your blood sugar?
No Do you have to cut carbs to reverse prediabetes?
No Does prediabetes always turn into diabetes?
No Do you have to be overweight to get prediabetes?
Quick calculators
Is my blood sugar normal?
Any fasting, after-meal, A1c or sensor number: its US band in both units and what to do next.
What does my A1c mean?
A1c to average glucose and mmol/mol, a sensor average to GMI, and when a change will show.
Prediabetes plan
Your weight target, your walking minutes and the date of your A1c retest.
Flatten the hill
One plate, three switches: carbs last, a walk after, a short night. Watch the hill change.
Is my sensor running high?
Your sensor number or report beside healthy people on a sensor, and what your fingertip would say.
Which spikes more?
Ten rounds of two foods. Tap the one that raises blood sugar more.
The blood sugar simulator
Pick a meal, press eat and watch the sugar move from your gut into your blood, liver and muscle, up to 100 times faster.
The meal index
248 everyday meals ranked by how much they raise blood sugar, with the carbs and GI behind each one.
Could I have prediabetes?
Eight taps scored like the CDC risk test: your score, your next test and the first three things to do.
How a meal becomes blood sugar
Mostly it's how much sugar and starch you eat. Watch it happen, see where your meals rank, and follow the food stop by stop.
The simulator
Pick a meal, press eat, and watch the sugar flow from your gut to your liver and muscle, up to 100 times faster.
The meal index
248 meals ranked: the 100 that raise blood sugar most and the 100 that keep it steady.
What happens when you eat
Pasta, a soda, rice, fruit, broccoli and a sandwich, told from your mouth to your muscles.
The guide
How blood sugar works: it's mostly how much you eat
How blood sugar works, in one map: the rise after a meal is mostly how much sugar and starch you eat. Fiber, fat, order, a walk and sleep change the speed.
Where blood sugar comes from and where it goes
Why moving your muscles lowers it
Sleep, late dinners and the morning rise
What is type 2 diabetes? How it develops, with the numbers- How insulin resistance builds
How to prevent type 2 diabetes: the habits that cut your risk
Can type 2 diabetes be reversed?
Can I manage blood sugar with lifestyle, or do I need medicine?- Should I take metformin? Diabetes medicines, the case for and against
