10 Surprising Causes of Blood Sugar Swings
DiabetesType 2 Diabetes

10 Causes of Blood Sugar Swings That May Surprise You

10 Causes of Blood Sugar Swings That May Surprise You
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Updated on December 15, 2025
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People with type 2 diabetes know how fickle blood sugar levels can be, as well as how important it is that they stay under control.

Proper blood sugar management is key for warding off a host of potential diabetes complications, and keeping your levels in check on a daily basis can help you feel good and stay energized and focused, says Lisa McDermott, RD, a diabetes specialist at Jefferson Hospital in Pittsburgh.

Learning how different habits can cause your blood sugar to fluctuate can help you better predict how your levels will swing, says McDermott. Managing the factors that can influence blood sugar can be a balancing act, and some of them may be out of your control, making it essential that you learn how to adjust accordingly.

1. Dehydration

Dehydration can be a sneaky cause of high blood sugar. Falling short on fluids can cause the sugar in your blood to become more concentrated, resulting in hyperglycemia, says McDermott. To make matters worse, high blood sugar can cause you to urinate more, which can further exacerbate dehydration.

People with diabetes should be especially vigilant about drinking plenty of water or other calorie-free beverages throughout the day to stay hydrated and healthy. Hydration goals vary depending on factors like sex and life stage, and people who are highly active or have more body mass have greater fluid needs.

If you find plain water hard to swallow, try garnishing your glass with a few citrus wedges, frozen berries, cucumber slices, or fresh mint leaves. Unsweetened iced herbal teas, such as raspberry, cherry, or peach varieties, are also wonderfully refreshing and naturally caffeine-free, says McDermott.

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2. Artificial Sweetener Consumption

Many people with diabetes reach for diet drinks as a substitute for regular soda or juice because they assume that sugar-free beverages won’t raise their blood sugar. But artificial sweeteners may not be completely neutral; in fact, they may contribute to impaired glucose homeostasis.

While the research isn’t definitive, and most government and medical institutions maintain that most artificial sweeteners don’t affect blood sugar, some of the possible downsides could be more present when artificial sweeteners are consumed in large amounts.

 For instance, if someone considers a sugar-free food or drink healthy, they may end up consuming excessive amounts of it. Or they may eat other high-carbohydrate foods because they think the diet drink doesn’t affect their total carbohydrate budget for the day.
It’s also possible that some noncaloric sweeteners called sugar alcohols, which include mannitol, sorbitol, and xylitol, can raise blood sugar levels and cause diarrhea, which can contribute to dehydration.

“If you drink a lot of diet soda, then you might want to cut back and see if it has an impact on your blood glucose,” says Patty Bonsignore, RN, CDCES, a nurse educator at the Joslin Diabetes Center in Boston. Keep things sugar-free by turning to water or seltzer as opposed to regular soda or juice.

3. Some Medications

Prescription and over-the-counter medications to treat conditions other than diabetes may have the potential to affect blood sugar levels.

For example, steroids (which are used to treat inflammatory conditions, autoimmune disorders, and asthma) can cause blood sugar to spike dramatically, says McDermott. Birth control pills, certain antipsychotic medications, beta-2 stimulators, and some hormone therapies may also cause higher-than-normal readings, while other drugs like antibiotics may lower blood sugar.

Make sure that your healthcare providers are aware of your diabetes diagnosis before they give you a new prescription. McDermott also recommends consulting your pharmacist before taking any new medications, regardless of whether they require a prescription or are available over the counter. Ask whether these products can interfere with diabetes management or interact with any other medications you’re taking.

4. Dawn Phenomenon

It’s not uncommon to wake up to a high blood sugar reading, even if your number was in the green zone when you went to bed.

You may be experiencing the dawn phenomenon, which occurs when the body prepares for waking up by releasing cortisol and other hormones between 2 a.m. and 8 a.m.

 These hormones make the body less sensitive to insulin and can contribute to a morning blood sugar spike in people with diabetes.

Alternatively, you may start the day with a low glucose level if, for example, you’re taking too much insulin or medication at night or not eating enough in the evening, says McDermott. Eating a small, protein-rich, low-carbohydrate snack at bedtime can sometimes help by shortening your fasting window without spiking your nighttime blood sugar.

If you see such trends in your morning readings or you find them highly erratic from day to day, work with your doctor or diabetes educator to identify the problem so you can take steps to correct it, says Bonsignore.

5. Women’s Menstrual Cycles

As if cramping, bloating, and mood swings weren’t enough, hormonal changes during a woman’s premenstrual phase can impact her blood sugar levels.

While the effect varies from person to person, some women with diabetes become less sensitive to insulin during the week or so leading up to their period, which can result in above-normal sugar levels, says McDermott. Readings typically return to normal once or soon after menstruation begins.

If you notice that your blood sugar consistently runs high the week before your period, McDermott says that it may help to reduce the amount of carbohydrates you eat during that time or squeeze in some extra exercise, tracking your cycle and blood sugar levels closely. And if you’re taking insulin, speak with your doctor or diabetes educator about possibly adjusting your medication to compensate for these hormonal changes.

6. Insufficient Sleep

Restless nights hurt more than your mood and energy — they may also spell trouble for your blood sugar. Getting too little sleep creates stress in the body, triggering the release of hormones including cortisol, which worsens insulin resistance and raises blood sugar levels.

“Sleep is restorative,” says Bonsignore. “Not getting enough sleep is a form of chronic stress on the body, and anytime you have added stress, you’re going to have higher blood sugar levels.”

Unfortunately, people with type 2 diabetes commonly report trouble sleeping, says McDermott. Those with a high body mass index are at a particular risk for sleep apnea, in which breathing frequently starts and stops during sleep.

To improve your sleep quality and duration, work to get into a consistent sleep routine in which you go to bed and wake up at the same time every day. Aim to log at least seven hours of sleep per night.

If you continue to experience sleep troubles or suspect that you have sleep apnea (perhaps your partner complains about your snoring), Bonsignore recommends reaching out to a sleep medicine specialist for support.

7. Extreme Weather

Whether it’s swelteringly hot or bitterly cold outside, extreme temperatures can interfere with diabetes control because people with type 2 diabetes vary in the way their body responds to heat, says Bonsignore. Some may see their blood sugar creep up on really hot days because the unpleasant conditions put extra stress on their system, while others (particularly those taking insulin) may experience the opposite effect, she says.

What’s more, high temperatures can affect the way the body uses insulin, potentially leading to blood sugar swings. Meanwhile, chronically high blood sugar levels can affect the body’s ability to regulate its temperature while also causing the body to lose fluids more quickly. The latter can further stoke blood sugar levels by increasing the risk of dehydration.

Bonsignore recommends trying to stay indoors during the hottest part of the day and monitoring your blood sugar closely for changes when temperatures start to rise.

8. Traveling

Skipping a few time zones during a long flight throws almost everyone off, but it’s an even bigger concern for people with diabetes. The time change can disrupt your medication schedule and lead to unusual eating and sleeping habits that also interfere with blood sugar control, says McDermott.

Plus, when you’re on vacation or traveling, you may eat more, drink more alcohol, or be more active, all of which can cause blood sugar swings. She advises checking your blood sugar more frequently while traveling to catch any concerning trends before they become serious problems.

McDermott also recommends packing healthy carbohydrate-balanced snacks and a refillable water bottle to help you stay hydrated. Try to eat something every four hours throughout the day, even if it can’t be at the exact times you typically eat. If you take insulin and you’re shifting time zones, be sure to work out a medication schedule with your diabetes care team before your trip so you don’t mistime any doses, she says.

9. Too Much Caffeine

Consuming up to 400 milligrams of caffeine per day is safe for most people, but in those with diabetes, the stimulant may affect how insulin behaves, which can lead to low or high blood sugar.

“Some people with type 2 diabetes can drink all of the caffeine they want, while others see blood sugar levels spike with just one cup of coffee,” says McDermott.

All you can do is monitor your blood sugar to observe how caffeine affects you. If you experience frequent blood sugar swings and are a heavy consumer of caffeinated beverages (which include diet soda as well as coffee and tea), Bonsignore recommends cutting back to see if your glucose control improves.

10. Blood Sugar Testing Mistakes

Lastly, blood sugar testing mishaps can lead to inaccurate results, raising red flags on blood sugar levels that may not be so problematic after all.

For instance, if you don’t remember to wash your hands before checking your blood sugar, you may experience a false alarm. Testing after handling food can also produce an erroneously high reading because sugar residues on the skin can contaminate the blood sample.

If your blood sugar reading comes back as higher than it really is, you could easily end up taking too much insulin, which could then result in dangerously low blood sugar levels, says McDermott.

Today’s blood sugar meters are highly sensitive because they use a very tiny draw of blood, which means it can be easy to throw off the glucose concentration in a sample. If you can’t get to a sink to give your hands a good scrub, you can improve testing accuracy by using the second drop of blood after wiping away the first.

The Takeaway

  • Blood sugar swings in people with type 2 diabetes can be caused by lifestyle factors like dehydration, insufficient sleep, and excessive caffeine consumption.
  • Artificial sweeteners, despite being sugar-free, may also impair glucose control, especially when consumed in large amounts, and sugar alcohols specifically can directly raise blood sugar.
  • Certain medications (like steroids and some antipsychotics) can cause blood sugar to spike, while others (like some antibiotics) can lower it, making it essential that you review all medications you take with your healthcare team to avoid such interactions.
  • Physiological events, including the dawn phenomenon, menstrual cycles in women, extreme weather, and traveling across time zones can contribute to blood sugar fluctuations as well.

Resources We Trust

EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
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  6. Non-Diabetes Medicines That May Raise Blood Sugar. Kaiser Permanente. July 7, 2025.
  7. FDA Drug Safety Podcast: FDA Reinforces Safety Information About Serious Low Blood Sugar Levels and Mental Health Side Effects With Fluoroquinolone Antibiotics; Requires Label Changes. U.S. Food and Drug Administration. January 14, 2022.
  8. The Dawn Phenomenon: What Can You Do? Mayo Clinic. November 12, 2022.
  9. Diabetes and Women. Centers for Disease Control and Prevention. May 15, 2024.
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  11. How Many Hours of Sleep Are Enough for Good Health? Mayo Clinic. February 1, 2025.
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  13. Tips for Traveling With Diabetes. Centers for Disease Control and Prevention. May 15, 2024.
  14. Caffeine: Does It Affect Blood Sugar? Mayo Clinic. March 7, 2024.
  15. Blood Sugar Testing: Why, When and How. Mayo Clinic. January 16, 2024.
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Sandy Bassin, MD

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Member of American College of Lifestyle Medicine

Sandy Bassin, MD, is an endocrinology fellow at Mount Sinai in New York City. She is passionate about incorporating lifestyle medicine and plant-based nutrition into endocrinology, particularly for diabetes and obesity management.

She trained at the Geisel School of Medicine at Dartmouth, where she taught culinary medicine classes to patients and medical trainees. She continued her training at the Robert Wood Johnson Medical School.

Dr. Bassin has published reviews of nutrition education in medical training and physical activity in type 2 diabetes in Nutrition Reviews, Endocrine Practice, and the American Journal of Lifestyle Medicine. She has been featured on the Physician to Physician Plant-Based Nutrition podcast and given many presentations on lifestyle interventions in endocrine disorders.

She stays active through yoga and gardening, and loves to cook and be outdoors.

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Johannah Sakimura is a registered dietitian and nutrition communications expert based in the New York City metro area. Johannah first joined the Everyday Health team as a health editor covering diabetes news. Prior to working at Everyday Health, Johannah served as Editorial Director of Health and Nutrition at Joy Bauer Ventures, where her work spanned broadcast, print, digital, and social media. She developed content for more than 200 nutrition and health segments on NBC’s Today show and contributed to numerous bestselling nutrition and weight loss books, including The Joy Fit Club: Cookbook, Diet Plan & Inspiration and the revised edition of Joy Bauer’s Food Cures. Her work has also appeared in O, The Oprah Magazine. Johannah has a bachelor’s degree in political science from Duke University and a master’s degree in nutrition from the Columbia University Institute of Human Nutrition.

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K. Aleisha Fetters is a Chicago-based fitness writer and certified strength and conditioning specialist who empowers others to reach their goals using a science-based approach to fitness, nutrition and health. Her work has been featured in various publications including Time, Men's Health, Women’s Health, Runner’s World, Self, O, U.S. News & World Report, and Family Circle.  She also creates editorial content and programming for Exos, a sports performance company.

Fetters earned both her bachelor’s and master’s degrees in journalism from the Medill School of Journalism at Northwestern University. She has written multiple books -- Give Yourself MORE, Fitness Hacks for Over 50, My Pocket Guide to Stretching -- and coauthored The Woman’s Guide To Strength Training. She is regularly interviewed as an expert on strength training, women's fitness, and mindset. She works with trainees in person and online.

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