7 Sneaky Things That Affect Your Blood Sugar Levels

Updated: Mar. 16, 2022

It’s important to be aware of these unexpected factors and foods that raise blood sugar levels when you have diabetes.

sugar cubes repeated on light pink background

Blood sugar levels matter

Hint: Certain medications can be a problem

Your blood sugar or blood glucose is the main sugar found in your blood; it’s your body’s most important source of energy. Over time, high blood sugar—which is toxic—can lead to many health problems, like heart disease, stroke, vision loss, and more. So it’s key that you keep your blood sugar levels under control.

The good news is that your body has an exquisitely controlled method to keep blood sugar levels in the safe zone, which is the hormone insulin. When blood sugar starts to rise, as it normally does after you eat, insulin goes up too, encouraging your body to use the blood glucose as energy or store it in the liver for future use. The bad news is that some people develop insulin resistance, a precursor to type 2 diabetes, and the hormone starts to lose its ability to keep blood sugar under control. And others may develop an autoimmune condition, type 1 diabetes, that destroys the insulin-producing cells in the body.

Many of the things you eat affect your blood sugar levels, particularly if you have diabetes, but there are other tricky things that have an impact as well. Here are some surprising things that can cause your blood sugar levels to be higher than you might expect.

woman in kitchen with bowl and spoon

Skipping breakfast

People who eat breakfast may be better able to resist fatty and high-calorie foods later in the day. One study, published in a 2015 issue of Public Health Nutrition, found that adults with type 2 diabetes who ate breakfast ate less later in the day. A morning meal—especially one that is rich in protein and healthy fat—seems to stabilize blood sugar levels throughout the day. A study of obese people with type 2 diabetes who took insulin, published in The Journal of Clinical Endocrinology & Metabolism, found that eating more at breakfast (but not a higher number of daily calories overall) resulted in weight loss, improved blood sugar control, and decreased the need for insulin. (Here are some other things that happen to your body when you skip breakfast.)

Hands holding a bacon cheeseburger over plate of fries

A high-fat meal

People with diabetes may worry about the carb contents of their meals, but research suggests that fat can affect blood sugar levels too. Although fat doesn’t directly affect blood sugar in the same way as carbohydrates, it can have an impact. In a review of studies published in 2017 in the International Journal of Health Sciences, researchers found an association between fat intake, type 2 diabetes, and impaired glucose tolerance. Fat causes carbohydrates to be digested more slowly. So if someone with diabetes is on insulin, the insulin might peak at the wrong time, earlier than the carbohydrates that are being digested. A 2013 study found that people with type 1 diabetes needed more insulin if they consumed carbohydrates with fat than if they consumed the same amount of carbs without fat. There is some evidence to suggest that the fat content of a meal increases insulin resistance.

Mug of coffee
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While population-based studies seem to indicate that a coffee habit can lower the risk of developing type 2 diabetes in the long run, evidence suggests that for people who already have diabetes, caffeine can be tricky and one of the foods that may potentially raise blood sugar. “It’s very individual,” says Aaron Cypess, MD, PhD, an investigator at the National Institute of Diabetes and Digestive and Kidney Diseases at the National Institutes of Health. “I don’t want to say don’t drink caffeinated coffee, but I’ll have a patient who’s like, ‘You know my blood sugar was 120 in the morning, and then I had a cup of coffee, black, no sugar, nothing added, and drove to work, and now it’s 200.’” Some people’s blood sugar levels may be more sensitive to the effects of caffeine than others, he notes. (Here’s how to make your coffee habit healthier.)

man sitting on couch sick with headache
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Whether it’s a cold, flu, or even a urinary tract infection, your immune system releases special germ-fighting chemicals that can throw your blood sugar levels out of whack. That’s why it’s important to make a “sick day plan“—special eating and drinking guidelines to help keep your sugar levels more balanced—says Dr. Cypess.  Staying hydrated (with non-caffeinated, non-sugar beverages) is critical. (Need advice? Here are some tips for drinking more water and staying hydrated). It flushes excess glucose out and helps every aspect of your body work better. People with diabetes should let their doctor know when they’re sick; they may recommend more frequent blood sugar testing or that you adjust your insulin dosage. Don’t make any changes without consulting a medical professional.

Tired young woman sitting on sofa at home

Skimping on sleep

A good night’s rest may be just the medicine your doctor ordered—especially if you have diabetes or are worried about getting it. A study published in 2018 in the journal Acta Diabetologica reports that people with diabetes and prediabetes (a precursor to type 2 diabetes) who have what’s known as “low sleep efficiency”—a measure of how much time in bed is spent sleeping—have poorer cognitive function than those with better sleep efficiency. Lack of sleep can raise cortisol levels which can contribute to insulin resistance and hyperglycemia. (Here’s what you need to know about the difference between hyperglycemia and hypoglycemia.)

Man lighting a cigarette

Smoking cigarettes

Obviously, a smoking habit isn’t healthy for anyone, but cigarettes are particularly dangerous for people with diabetes. Whether you have type 1 or type 2, smoking increases your odds of serious diabetes-related complications, such as heart and kidney disease, vision loss, nerve damage, and poor blood flow in the legs and feet that can lead to infections, ulcers, and possible amputation, according to the Centers for Disease Control and Prevention. (Here’s everything you need to know about the A1C diabetes test.)

Man looking into medicine cabinet, holding pill bottle

Certain drugs in your medicine cabinet

Common drugs, including corticosteroids (such as prednisone or hydrocortisone) that are used to control asthma, COPD, and rheumatological condition can raise blood sugar levels, as can statins to improve cholesterol levels, and diuretics to lower blood pressure. Even joint or spine injections with hydrocortisone can cause hyperglycemia. Many of these drugs are important for other conditions, so if you use them, you might need to track and control your blood sugar levels more closely.