Common Causes of Blood Sugar Spikes

Medically Reviewed by Michael Dansinger, MD on December 12, 2022
5 min read

Because you have type 2 diabetes, you know it’s a must to keep your blood sugar levels under control. But do you know what makes them spike?

Check this list of common culprits, plus ways to help you stay healthy and feel great.

Watch what you eat since that's one of the most important things you can do to control your blood sugar, also called blood glucose.

That’s because of the impact that carbohydrates -- the sugars and starches in foods -- can have.

It’s fine to eat them in moderation. But choices that have too many carbs can cause your blood sugar to soar -- white rice, pasta, and highly processed or fried foods are examples. Some fruits are high in sugar, such as bananas. It’s OK to have fruit, just not too much.

Choose good carbs, like whole-grain bread and cereal, unprocessed grains such as barley or quinoa, beans, whole-wheat pasta, brown rice, fruit, yogurt, and vegetables.

Fiber helps because it lowers blood sugar. Good choices are whole grains, fruits that are lower in sugar (apples and blueberries), veggies, and legumes.

Start with a good breakfast. If you skip the first meal, your blood sugar is more likely to be too high after lunch and dinner. But don’t just reach for a muffin. One study found that people who ate a 500-calorie breakfast with at least 35% protein had lower post-meal blood sugar throughout the day than those who ate a breakfast lower in protein and higher in carbs.

That’s because protein helps slow your digestion. That makes your blood sugar rise more slowly after meals. And eating fewer carbohydrates means your body makes less blood sugar.

Eat a healthy dinner, too. Blood sugar is usually hardest to control later in the day. That’s why many experts say you should choose a dinner or after-dinner snack low in carbohydrates, especially the processed kind. Fat and protein don’t cause blood sugar to rise the same way carbs do. If you’re not sure how to balance your meals, ask your doctor for a referral to a dietitian who specializes in diabetes.

Plan when you eat. If you have diabetes or prediabetes, having meals and snacks too close together may not give your blood sugar level time to drop naturally after you eat. Make sure your meals are 4 to 5 hours apart. If you need a snack, do it 2 to 3 hours after your last meal.

Not getting enough rest does more than make you groggy. It also affects how well your body can control and break down blood sugar. Skimping on sleep, even for one night, makes your body use insulin less efficiently. That can make your blood sugar higher than it should be.

In one study, researchers asked healthy adults to sleep just 4 hours a night for 6 days. At the end of the study, their bodies’ ability to break down glucose was 40% lower on average. Why? Doctors believe that when you enter deep sleep, your nervous system slows down and your brain uses less blood sugar.

Get your shut-eye. Remember all the things that help: Stick to a regular schedule, don't use your phone or tablet close to bedtime, and relax before you hit the hay.

Even a mild workout, like walking or doing light housework, can lower your blood sugar and improve how your body responds to insulin. Research shows that a 15-minute stroll after dinner can help bring blood sugar down. Even better: It can help keep it down for up to 3 hours. When you exercise, your body pumps more sugar to your muscles.

When you don’t move around enough, your glucose levels can rise. Too much exercise can have the same effect. Tough activities, like bench-pressing weights, or competitive ones, like running a race, can raise your blood sugar.

That doesn’t mean you can’t sweat it out. Exercise is one of the best things you can do for your whole body. But ask your doctor what changes you may need to make in your treatment plan to keep your blood sugar in the right range.

When you’re really under pressure, your body releases hormones like cortisol and adrenaline. This is your fight-or-flight response. It prompts your body to act like it’s under attack.

Your body burns its stored energy sources -- glucose and fat -- to meet the threat. When you have diabetes, insulin can’t break through the cells to break down the glucose, and your levels rise.

Stress can also cause blood sugar to rise indirectly. You may be less likely to take care of yourself by eating right, exercising, or taking your medicine when you’re stressed out.

Because you can’t avoid all stress, finding ways to relax is good for your blood sugar and your overall health. Try meditation, yoga, or massage.

You know that insulin can bring your blood sugar down. But if you miss a dose or take the wrong dose of your medicine, you could cause your levels to spike. Some drugs, such as corticosteroids, can have the same effect. Other meds that could raise your glucose include:

  • Diuretics (“water pills”)
  • Drugs used to treat depression
  • Blood pressure medicines

If you’re on any of these medicines and you notice your blood sugar is high, talk to your doctor. They may adjust your diet or medications.

If you have diabetes, you’re more likely to get gum disease (also known as gingivitis). And serious gum disease can make it harder to keep your blood sugar under control. Like all infections, it may cause your glucose to rise. That, in turn, can make other infections more likely. Inflamed or infected gums can also cause your body’s defense system to go into overdrive. That makes it harder for your body to keep insulin and blood sugar in check.

Make sure you not only brush and floss your teeth but also rinse with an antiseptic mouthwash daily.

Keep up with your dentist visits, work on managing your blood sugar, and, if you have gum disease, treat it -- and any other infection in any part of your body -- ASAP.

If you light up, you raise your chances of getting diabetes. If you already have diabetes, you’re more likely to have trouble finding the right dose of insulin and controlling your blood sugar. Smoking makes it harder to keep your blood sugar levels down.

The lesson here: If you smoke, quit.

Blood sugar levels go up from time to time. But knowing what can cause these spikes can help you control them -- and avoid health problems down the line.

Drink plenty of water. When you’re dehydrated, your glucose may be higher than it would normally be.