Mary is a freelance nurse writer specializing in making healthcare and medical content accessible for people at all levels of health literacy. Her MSN in nursing education prepared her to deliver accurate and trustworthy medical information that educates and empowers the public.
Do-Eun Lee, MD, has been practicing medicine for more than 20 years, and specializes in diabetes, thyroid issues and general endocrinology. She currently has a private practice in Lafayette, CA. 
Diabetes is a medical condition in which your body cannot fully control blood sugar levels. Healthy blood sugar levels help your body’s processes work effectively.
You may detect blood glucose spikes when you check your blood sugar level. These spikes are temporary rapid increases in blood sugar. Understanding how and why they occur can help you avoid or manage your sugar spikes better. High blood sugar levels over time can cause serious complications and health issues.
This article discusses several potential causes of blood sugar spikes.
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You may not be aware of high blood sugar levels, which can spike even if you haven’t eaten. Symptoms of high blood sugar (called hyperglycemia) include increased thirst, frequent urination, and elevated levels of sugar (glucose) in the urine.
Checking your sugar levels about two hours after eating can help identify blood sugar spikes from the foods you consume. It's normal for blood sugar levels to rise after eating.
Carbohydrates, especially those higher on the glycemic index, tend to cause rapid increases in glucose levels. Foods lower on the glycemic index scale and those with higher fiber levels have been shown to cause fewer blood sugar spikes.

The glycemic index is a scale that helps rank foods based on how likely they are to increase blood sugar levels.
A healthcare provider or dietitian can help you understand how different foods affect your blood sugar levels. They can help you with food choices and determine when you may need to adjust your medications for the best blood sugar control.

Exercising moderately for 150 minutes each week helps control blood sugar. For many people, exercise can increase the sensitivity of cells to insulin, so that blood sugar is better absorbed.
Physical activity can also help bring sugar into cells even without insulin. One study showed a 20-minute treadmill walk after dinner helped reduce post-meal blood sugar spikes.
However, some exercises, like weight lifting and sprinting, can increase blood sugar. These activities can cause your body to release the stress hormone adrenaline, which typically increases blood glucose levels.

Adequate, quality sleep is important in blood sugar control. A study of healthy adults showed that sleep duration, quality, and bedtime (called sleep midpoint) all helped to control post-breakfast blood glucose levels.
Another study also found that sleep duration and quality are important in the blood sugar control of people with diabetes; however, bedtime was not an important factor in this study. More research may help clarify that difference.
Physical and emotional stress can trigger blood sugar spikes in some people. Learning ways to manage your stress is vital to your long-term health.
Cortisol is a hormone your body releases in times of stress, causing an immediate release of sugar into your bloodstream. Over time, elevated cortisol levels lead to long-term increases in blood sugar levels. Researchers are studying whether cortisol decreases insulin production and/or insulin sensitivity.
Strong emotions can also trigger some people to eat. Some people eat foods they find comforting, like ice cream or potato chips, to cope with stress. Other times, loneliness or boredom may be a source of stress and uncomfortable feelings that trigger someone to eat. You may see blood sugar spikes if you choose high-glycemic-load foods during stressful moments.

Many medications can affect your blood sugar levels. Make sure everyone on your healthcare team knows all your medications and supplements and that you update them if you change doses or stop taking any.
Some medications that can potentially cause blood sugar spikes include:
This is not a complete list of medications that can affect your blood sugar levels. Speak with your pharmacist or provider about any concerns you have.

Being sick or having an infection can raise your blood sugar levels. Infections can occur in different parts of your body and include pneumonia, urinary tract infections (UTIs), or foot wounds. The risk for infections and sepsis is higher than average for people with diabetes.
Illness and infection are physically stressful to your body and cause the release of cortisol and other stress hormones. They can also affect what you eat, how often you eat, and your activity levels. These can all potentially cause blood sugar spikes.
If you have been diagnosed with diabetes, be sure you ask your healthcare team for a plan to manage your blood sugars for when you get sick.

Not having enough fluid in your body (dehydration) can cause blood sugar spikes. As you lose fluid, the sugar in your body becomes more concentrated, and the sugar level in your bloodstream increases.
Hot weather, extreme exercise, high blood sugar levels, vomiting, and diarrhea can all lead to dehydration in a person with diabetes. If you cannot replace the lost fluids or control your blood sugars, seek medical treatment immediately.

Smoking has been shown to make blood sugar levels harder to control, no matter what kind of diabetes you have. Nicotine, a chemical in cigarettes, increases blood sugar levels.
Quitting smoking improves insulin sensitivity and can help with blood sugar control. If you smoke, quit as soon as possible. Your healthcare provider may have treatments and assistance available to help you stop smoking.
Circadian rhythm, meal times, and time of day can all play a role in sugar spikes. The body’s internal clock adjusts to exercise, insulin release, and insulin sensitivity throughout the day.
Blood sugar levels naturally spike in the early morning (before 4 a.m.), but the body is less able to control sugar levels in the evening. Blood sugar spikes can occur throughout the day.
Follow your healthcare provider’s instructions on how and when to check your blood sugar levels. Some people use a continuous glucose monitor, but others need to check their sugar with a glucometer (blood glucose monitor).

Morning spikes of blood sugar typically have one of three causes:
You may be directed to keep a log of your medication timing, food, and activity to review with your healthcare provider to better understand and treat any morning spikes you are having.
Having diabetes puts you at risk for several diabetic emergencies (hypoglycemia, hyperglycemia, and more). Be sure you know the signs and treatments for each. Seek medical treatment immediately by calling 911 if you are experiencing one of these emergencies.
Blood sugar spikes have many different causes. Some are easy to understand and avoid, and others are potential emergencies. Be sure you know the treatment plan and medications you have been prescribed for managing your diabetes. If you have any symptoms of abnormal blood sugar, check your level immediately and get emergency help if needed.

If you experience blood sugar spikes, you may find them frustrating or terrifying, depending on the cause. Understanding different reasons for short-term spikes in blood sugar can help you know what to expect and may even help prevent the problem. There are support groups for people with diabetes, and your healthcare team is ready to support you.

Carbohydrates, especially those high on the glycemic index, are common culprits of a blood sugar spike. Testing your blood sugars before and after eating different foods can help you understand how your unique body responds to different foods.
Work with your healthcare provider to understand how your medications work and your plan for a blood sugar spike. Moderate exercise can often help to lower blood glucose levels.
High blood sugar levels can occur in people without diabetes for many different reasons. Some are similar to people with diabetes, and some are different.

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