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5 Surprising Reasons Your Blood Sugar Is High

Written by: Michele Ross

Reviewed by: Emily J., MSc RD

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two women standing over a kitchen counter and studying data on a phone screen

2022-09-16

8 minutes

Diabetics aren’t the only ones who can experience hyperglycemia. Discover five surprising causes of blood sugar rises in non-diabetics and symptoms to look out for.

Keeping your blood sugar levels within healthy ranges has a number of benefits, both in the short and long term. Maintaining blood sugar stability can help with everything from your day-to-day energy levels and focus, to future health outcomes and overall sense of well-being as the years go by.

Ultimately, being proactive is essential when it comes to blood sugar balance, which is why we’re covering the basics of non-diabetic hyperglycemia, symptoms of high blood sugar, and some sneaky causes of blood sugar rises in non-diabetics.

What Is Non-Diabetic Hyperglycemia?

Though hyperglycemia (or elevated blood sugar levels) is often associated with diabetes, non-diabetics can experience it too.

Fasting blood sugar between 70 and 100 mg/dL[1] is considered to be normal. As a large 2022 study[2] from Japan published in the Journal of Diabetes Investigation discovered, the risk of developing diabetes was progressively higher in adult participants with a fasting plasma glucose concentration of 90 to 99 mg/dL. (In addition, non-diabetic hyperglycemia involves high fasting blood sugar from 100 to 125 mg/dL, plus elevated readings after eating.)

Meanwhile, post-meal glucose rise over 30 mg/dL also points to non-diabetic hyperglycemia. Ideally, this variability will max out at around 20 mg/dL to avoid the release of excess insulin, which your body won’t be able to handle properly. In a 2019 study[3] published in the journal Medicine, researchers found that the risk of cardiovascular disease and mortality in a general non-diabetic population was greater in subjects with higher glycemic variability. This underscores the importance of minimizing glucose fluctuations — even in healthy, non-diabetic individuals.

If you don’t have a CGM just yet and are curious about the main symptoms of high blood sugar in non-diabetics, you’ll want to pay attention to the following[4]:

increased thirst/hunger
frequent urination
headaches
fatigue
blurred vision

However, symptoms aren’t always apparent and instead can take months or even years to manifest — which emphasizes how important personalized insights from a CGM and regular check-ins with your doctor are to stay on top of your metabolic health.

What Causes Blood Sugar to Rise in Non-Diabetics?

Here’s a closer look at five key causes of blood sugar rises in non-diabetics.

1. Diet

Some foods are more likely to spike your blood sugar even if you’re metabolically healthy, such as refined carbs, processed foods, sodas, and items that contain added sugar. If you have a sweet tooth or carb cravings that tend to veer you off course from an otherwise healthy diet, you’ll want to be extra cautious of sudden rises in blood sugar, which over time can lead to insulin resistance, i.e., how responsive your cells are to insulin, the hormone that regulates the amount of glucose in your blood and “unlocks” cells so they can turn glucose into energy.

As you’re grocery shopping or putting together your meals for the week, try to prioritize low-glycemic foods, i.e., foods that are under 55 on the glycemic index (GI). The glycemic index (GI), which ranks foods on a scale of 1-100 based on how much it makes your blood sugar rise (pure glucose has a score of 100). The lower the number, the slower your blood sugar will rise[5] after eating that particular food. Foods that are high in added refined sugars or flours tend to have a higher GI, whereas foods that contain fats and/or fiber (which slow the absorption of carbohydrates) tend to have a lower GI.

But GI isn’t the whole picture. Glycemic load (GL) is a more complete indicator of actual blood sugar impact. It takes the glycemic index[6] and multiplies it by the number of carbohydrates per serving of that food (and then divides by 100 for simplicity’s sake). So a food with a glycemic index of 55 and 10 grams of carbs per serving would have a glycemic load of 5.5.

Whole fruit is a great example of why this is helpful. Many fruits rank high on the glycemic index but actually have a low GL, since a single serving of fruit doesn’t actually have a significant amount of carbohydrates per serving (thank you fiber!). If we had just looked at GI we might have avoided it. GL tells us that this food may have a lower glucose response.

Some overarching tips on diet:

Look at both GI and GL, and try to keep the numbers under 55 and 10, respectively.
Fiber can help slow the absorption of carbs and keep blood sugar levels stable, so opt for whole fruits and smoothies over fruit-based juices (even fresh-pressed or -squeezed). Even better if you consume them with a healthy fat.

2. Dehydration

Staying hydrated is one of the best things you can do to promote overall well-being — and that includes promoting metabolic health. According to a 2017 entry in Nutrition Research[7], research demonstrates that consistently low water intake is associated with an increased diagnosis of non-diabetic hyperglycemia. (Less water means less blood volume — which in turn results in a higher concentration of glucose in your blood.)

There are countless causes — some of which may be surprising — that can contribute to dehydration, which naturally includes not drinking enough H2O but also:

sweating excessively,
high altitudes (at which your respiration rate and urine output increase),
low-carb diets (carb-rich foods tend to have more water and electrolytes; additionally, when your body uses up its glucose stores, it has a diuretic effect),
diarrhea,
aging (your body naturally contains less water the older you get),
breastfeeding, and
not eating enough water-rich foods such as cucumbers, celery, and watermelon.

3. Meal Timing

A key component of stabilizing your blood sugar isn’t just paying attention to what you eat, but also when. As it turns out, your body’s insulin sensitivity isn’t static — it fluctuates throughout the day. As noted[8] in The Federation of American Societies for Experimental Biology, there is an intrinsic “circadian rhythm in insulin sensitivity,” with reduced sensitivity/higher blood sugar levels at night (which means it’s best to space out your carb intake throughout the day and avoid saving it up for dinners or evenings). If you’re curious about how to create a meal timing schedule, consider practicing time-restricted feeding or intermittent fasting, where you consume all of your meals within an eight-hour window and fast for 16 hours before your first meal the following day.

Ever wonder why your blood sugar is higher in the morning? The “dawn phenomenon”[9] — in which the liver revs up glucose production, prompting your body to rise and shine — can cause high blood sugar levels especially if insulin can’t keep it in check.

4. Genetics

If metabolic dysfunction runs in your family, you may be at greater risk of developing non-diabetic hyperglycemia[10].

However, the good news is that a family history of diabetes doesn’t guarantee that you’re destined to struggle with metabolic issues. By eating the right foods (which includes knowing and limiting the ones that cause your blood sugar to rise; a CGM comes in handy for this very purpose) and practicing healthy lifestyle habits, you’ll have a better chance of maintaining healthy glucose levels.

5. PCOS

Polycystic ovarian syndrome (PCOS) is a common hormonal disorder amongst women of reproductive age that can negatively impact metabolic health. According to a medical review[11] in Reproductive Health, as many as 50 percent of women with PCOS are insulin resistant.

Insulin is necessary to maintain steady blood sugar levels; an excess of it and/or resistance to it permits glucose to build up in the blood, resulting in high blood sugar levels.

Key Takeaways

If you’re non-diabetic yet have high fasting blood sugar, you’ll want to take care to address any underlying causes of blood sugar rises before it evolves into more serious health issues. While your family history and certain health conditions such as PCOS may heighten your risk of non-diabetic hyperglycemia, we hope you’ll be empowered by the fact that you can mitigate your risk through healthy dietary and lifestyle habits.

Of course, limiting your intake of certain foods and being mindful of eating patterns that can cause high blood sugar is key. But it’s just as important to keep your body moving, get enough sleep, and manage stress on a consistent basis to avoid insulin resistance and ultimately normalize — blood sugar levels.