10 Surprising Causes of Blood Sugar Swings

Can dehydration cause high blood sugar? Yes, and it turns out, the two are more related than you may realize: Falling short on fluids can lead to hyperglycemia, as the sugar in your circulation becomes more concentrated, McDermott explains. To make matters worse, high blood sugar can cause you to urinate more, resulting in even more 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. Plus, people who are highly active or have high body mass levels have greater fluid needs. If you find plain H2O 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, she says.

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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 a review published in 2021 suggested that artificial sweeteners may not be completely neutral after all, and may contribute to impaired glucose homeostasis.

But the research isn’t definitive — most government and medical institutions maintain that most artificial sweeteners do not affect blood sugar. So what could be going on? According to the Mayo Clinic, some of the possible downsides to artificial sweeteners could be more present when consumed in large amounts. (This could be because some consider sugar-free food healthy, so they end up consuming excessive amounts or eating other carb-filled foods because they think the diet drink lets them “afford” it.) The Mayo Clinic also notes 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.

The prescription and over-the-counter medications you take to treat health problems besides diabetes can monkey with blood sugar levels. One example is steroids (used to treat inflammatory conditions, autoimmune disorders, and asthma), which can cause blood sugar to shoot up dramatically, McDermott says. Birth control pills, certain antidepressants and antipsychotics, beta-2 stimulators, and some hormone therapies may also cause higher-than-normal readings, while other drugs, such as antibiotics, may lower blood sugar, according to TriHealth. “Even cough drops can affect blood sugar levels,” she says.

Make sure your prescribing physicians are aware of your diabetes before giving you a new Rx, and consult with your pharmacist before taking any new medications, prescription or not, McDermott advises. Ask whether these products will interfere with diabetes management or interact with any other meds you’re taking.

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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 preps for waking up by releasing cortisol and other hormones, between 2 and 8 a.m., according to the Mayo Clinic.

These hormones make the body less sensitive to insulin, and in people with diabetes, can contribute to a morning blood sugar spike. 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, McDermott says. She notes that eating a small, protein-rich, low-carb snack at bedtime can sometimes help by shortening the fast (without spiking nighttime blood sugar).

If you see a trend in your morning readings — or they’re highly erratic from day to day — you’ll want to work with your doctor or diabetes educator to identify the problem so you can take steps to correct it, says Bonsignore.

As if cramping, bloating, and mood swings weren’t bad enough, hormonal changes during a woman’s premenstrual phase can cause her blood sugars to get a little out of whack, according to the CDC.

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 translate into above-normal sugar levels, McDermott explains. 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, it may help to trim the amount of carbohydrates you’re eating during that time or squeeze in some extra exercise, she says. (Just be sure to track your cycle and blood sugar levels closely to be certain this is the cause.)

If you’re taking insulin, speak with your doctor or diabetes educator about possibly adjusting your medication to compensate for hormonal changes.

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Restless nights hurt more than your mood and energy — they may also spell trouble for your blood sugar. A review published in 2015 concluded that a lack of sleep may hinder glucose control and insulin sensitivity in people with type 2 diabetes.

“Sleep is restorative,” Bonsignore says. “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, McDermott says. Those with a high body mass index are at 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 where you go to bed and wake at the same time every day. Your goal: Nab at least seven hours of sleep per night, per recommendations from the National Sleep Foundation. If you continue to have sleep troubles or suspect you have sleep apnea (for instance, maybe your partner complains about your snoring), reach out to a sleep medicine specialist for support, Bonsignore says.

Whether it’s swelteringly hot or bitterly cold outside, extreme temperatures can interfere with diabetes control. That’s because people with type 2 diabetes vary in the way their body responds to heat, Bonsignore says. Some may see their blood sugar creep up on really hot days because the unpleasant conditions put extra stress on their system; 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 and potentially lead to blood sugar swings, according to the CDC. It also notes that 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. Try to stay indoors during the hottest part of the day, and monitor your blood sugar closely for changes when the mercury starts to rise, recommends Bonsignore.

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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 cause unusual eating and sleeping habits, which interfere with blood sugar control, McDermott says.

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 carb-balanced snacks as well as 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 same times you usually 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.

According to the Mayo Clinic, consuming up to 400 milligrams (mg) of caffeine per day is safe for most people, but in those with diabetes, the substance may affect how insulin behaves, which can lead to low or high blood sugar. Prior research suggests that consuming too much caffeine may cause blood sugar levels to spike in those who already have the disease. To make things even more confusing, a different study, published in 2015, suggested that caffeine intake can actually improve how the body manages blood sugar and reduce the risk of diabetes-related complications.

It may depend on the person. “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,” McDermott says.

All you can do is monitor your blood glucose 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), consider cutting back to see if your glucose control improves, Bonsignore recommends.

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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 produce an erroneously high reading because sugar residues on the skin can contaminate the blood sample, research has shown. If your blood sugar readings come back as higher than it really is, you could easily end up taking too much insulin, McDermott says. The result: dangerously low blood sugar levels.

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 the 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.