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17 Causes of Blood Sugar Swings and Fluctuations

Katrina Larsen, MS, RDN, CDCES

Published in Glucose

10 min read

December 6, 2021
October 12, 2023
a person looking at their glucose chart in the Nutrisense app
a person looking at their glucose chart in the Nutrisense app

Managing your blood sugar levels is essential when you're learning to live with diabetes. But having large swings in blood sugar can be harmful even if you don’t have a diabetes diagnosis.

Whether you’re making necessary lifestyle modifications or not, there are other things to consider with or without a diagnosis. After all, high glucose levels can sometimes be an indicator of a potential diabetes diagnosis. So, while watching what you eat is an effective way to control blood sugar, remember that there are various other factors that can also affect your glucose.

Keeping track of these is vital because ignoring them can potentially disrupt your efforts at managing your blood sugars. And even if you don’t have diabetes, your blood sugar still affects your sleep, how you feel throughout the day and may even determine how long you live.

Of course, how, what, and when you eat is still a core component when measuring your blood sugar. But to make managing blood sugar levels easier, here’s a list of some other causes of fluctuations to watch for:

1) Morning Hormone Levels (Dawn Phenomenon) 

a person sleeping in a bed

You’ve probably heard the phrase “body clock.” If you don’t already know, this means that with or without an alarm to coax you out of bed, you will usually wake up around the same time every morning (save for that late night out partying!).

This “dawn phenomenon” is the consequence of a measurable, chemical response within your body. In line with our diurnal lifestyles (in contrast to some animals’ nocturnal tendencies), the body produces certain hormones. These encourage you to wake up sometime after the sun rises to take advantage of all that beneficial daylight. 

These sleep/wake cycles result from those hormones inciting your body to produce extra blood sugar, giving you a much-needed shot of energy to start the day. While this is a welcome evolutionary edge, it can sometimes come at the cost of skewing your blood glucose levels, at least temporarily. Check out our article on morning blood glucose to learn more about this phenomenon and other blood sugar quirks you might experience after waking up.

2) Your Hydration 

It’s no secret drinking water is good for you. And human beings really are mostly water: the liquid portion of your blood (the plasma) is made of over 90 percent of water. With water’s tendency to dilute substances that it’s mixed into, the more water you drink, the more excess blood sugar is washed out of your blood through your urine and endocrine system. In contrast, the closer you are to dehydration, the more concentrated your blood sugar levels can become

3) Extreme Weather Conditions 

If dehydration can spike blood glucose, it’s no surprise that you should also be monitoring other conditions that cause water loss in your body. For example, you sweat when it’s hot, and when you sweat, you lose more water than usual. This can then put you at risk of blood sugar-related complications. An increase in glucose is often seen with heat exposure—this can be due to changes in fluid related to heat as well as stress responses to heat. 

two bowls of vegetables

4) Sugar-free Foods 

Particularly insidious is the effect of artificial sweeteners, often found in foods labeled as sugar-free (or “diet”), to provide a sweet kick without the guilt of natural sugar. It’s not yet clear why, but recent studies show that the body can react negatively to these sweeteners, paradoxically spiking blood sugar despite the absence of any actual sugar. 

Further damning these sweeteners are their measured effect on insulin resistance. Your body can be tricked into treating artificial sweeteners similarly to sugar, producing excess insulin in response and building insulin resistance, a precursor to diabetes. 

While sugar-free foods help you keep daily calorie counts low, manage diabetes, and maintain a healthy weight, it’s a good idea to eat foods containing artificial sweeteners in moderation.

5) Cold Medications 

Artificial sweeteners find themselves included in much more than sugar-free foods. It’s worth the time it may take to read ingredient labels to see if sweeteners have made their way into anything you consume regularly. This can include over-the-counter medicines, which may contain artificial sweeteners to mask their bitter taste and make them more palatable. Depending on how your body responds to artificial sweeteners, it may be better to select a pill that’s harder to swallow but easier on your blood sugar levels. 

6) Birth Control 

Evolving research has shown associations between contraceptives that affect the hormones relevant to reproduction (like birth control pills, rings, implants, and patches) and blood sugar levels. If you’re pre-diabetic or have diabetes, it’s a good idea to speak with your doctor about what birth control is best for you. 

7) Steroids 

Medical conditions that demand taking anti-inflammatory medications may call for regular doses of steroids. No matter how they’re administered, many steroids are known to increase blood glucose levels. This is due to the hormones they encourage your body to release, causing your liver to subsequently release stored glucose. 

8) Lack of Sleep

a person having insomnia

We’ve gone over the effects of sleep on blood sugar and vice versa. But here’s the most crucial role sleep plays in controlling blood sugar: the less consistent rest you get, the less your body can regulate the hormones it secretes. 

Certain hormones in your body can change how it reacts to insulin. If you become more insulin resistant, you’re less able to naturally regulate your blood sugar levels. Taken to an extreme, this can spiral into a cycle of further increasing insulin resistance, causing less and less blood glucose regulation, ultimately leading to diabetes complications. 

9) Caffeine Consumption

a pot of coffee, a cup of coffee and a bowl of coffee beans

Besides potentially ruining a night of good sleep, caffeine may produce other measurable effects on blood sugar levels. Unfortunately, there’s no consensus on what factors are at play or whether diabetics are particularly sensitive to caffeine consumption. Remember, there’s no one-size-fits-all here! So, there’s no consensus yet on who might see their blood sugar levels drop, instead of rise, from caffeine intake. Your best bet is to experiment to see how your body responds to caffeine. As with any new additions to your diet and lifestyle, approach this cautiously and consider getting personalized advice from a doctor or dietitian. 

10) Menstrual Cycles 

The pattern of hormones and their relation to blood sugar fluctuations continues with another significant influence on hormonal balance. Like birth control, your menstrual cycle can spike your blood glucose levels through the body’s natural reaction to the increased levels of the specific hormones released. 

Experts recommend caution when reacting to such spikes, so if you have diabetes and are on insulin, don’t go increasing your insulin in response. It may inadvertently leave you overly sensitive if your sugar levels return to normal more rapidly than you anticipate.

11) Alcohol Consumption 

Drinking excessively is always a bad idea, but remember that even a moderate amount can affect your blood sugar levels. When alcohol is broken down, much of the glucose management occurs in your liver. Instead of occupying itself with releasing glucose promptly, your liver can become distracted with breaking down any alcohol recently consumed, potentially leading to a drop in your sugar levels. It’s a good idea to drink in moderation and track and monitor how alcohol reacts to your body when you do. 

12) Exercise 

a couple of people doing exercises in the morning

Exercise is part of the foundation of a healthy lifestyle. It has even been found to reverse the onset of prediabetes. So it might seem unfair that you still have to be mindful of your blood sugar levels when exercising as part of your diabetes management plan.

The type and intensity of the exercise can play a role in whether your sugar levels rise or fall, but what may matter even more is if you’re exercising fasted or fed. If you’ve just eaten, your body has the energy to get through an exercise routine before your liver starts secreting more of its stored glucose to supplement it. At the end of the day, regular exercise has a net beneficial effect on your blood glucose, so there’s no reason to avoid it!

If you have diabetes or want to know more about how exercise impacts your blood glucose, speak with a health professional to develop a safe and effective exercise plan. 

13) Stress 

Your body naturally responds to the demands of any extra exertion by producing hormones to tell itself to release its stored energy. When that energy source is glucose, it spikes your blood sugar levels. The signal to release that energy is your fight-or-flight response. It doesn’t discriminate between exertion through regular exercise or through other sources of stress. 

Humans developed this response as a way to exert a lot of energy really quickly if and when necessary. This is great if you’re being chased by a tiger but not always suitable for other sources of stress. Daily ups-and-downs and one-off instances of anxiety can trigger the same response, affecting your glucose levels in the same way. 

14) Depression 

Depression is a broad condition that can have elevated incidences among those with diabetes. Suffering from depression doesn’t necessarily affect your blood sugar on its own. Still, the correlations are well established and are likely consequential to how you react to a diabetes diagnosis. So, while stress and depression can affect everyone, managing diabetes can make everything more challenging. 

15) Gut Health 

Recent studies have shown promising correlations between your gut flora, the bacteria living within the gastrointestinal system, and secondary associations with your blood sugar. Certain bacteria (though it’s still uncertain which) can influence your liver to release its stored glucose

While this is still being explored, remember that balanced diets (including recommended amounts of fiber, prebiotics, and probiotics) may help regulate and feed the bacteria in your gut. This may be able to ensure blood sugar control and a balance of the types of bacteria that live within you. 

a bowl of porridge with banana, nuts and berries

16) "Naked" Carbohydrates 

High-carb foods are a guilty pleasure for all of us, so don’t worry too much about the occasional craving. But a diet that’s primarily filled with high-carb foods may be cause for concern. If you have diabetes or have been working with a dietitian or nutritionist you may already know the body breaks down carbohydrates into sugar. Naturally, more sugar will raise your blood sugar levels, so remember to monitor and moderate this.  

Things get more complicated when it comes to complex carbohydrates. A complex carb is a carb whose molecular structure is more complicated than those associated with simple or “naked” carbs. For example, when you eat whole grains, where the carbohydrates remain molecularly unbroken, your body takes longer to disassemble the molecules into their simple constituent sugars.

In contrast, if you eat something that’s heavily milled and processed (like plain pasta or white bread), you may see a blood sugar spike in response to the carbs being so easily and rapidly broken down. 

17) Altitude 

High altitudes can put you at risk of both hypoglycemia and hyperglycemia. This doesn’t necessarily include air travel, where conditions are controlled to emulate surface conditions (though we still recommend speaking with your doctor before flying). If you have diabetes and you’re planning a high-altitude hike or a trip somewhere high above sea level, it’s a good idea to monitor your glucose levels.

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Kara Collier, RDN, LDN, CNSC

Reviewed by: Kara Collier, RDN, LDN, CNSC

Kara Collier is the co-founder and VP of Health at Nutrisense, one of America’s fastest-growing wellness-tech startups, where she leads the health team. She is a Forbes 30 under 30 recipient, frequent podcast guest & conference speaker.

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