Does Dehydration Cause High Blood Sugar? Here's What a Dietitian Says

 When you think of all the things that can impact your blood sugar level, hydration may not be the first thing that comes to mind. But it plays an important role. "People believe that it's just diet and weight, but there are so many other factors that impact blood sugar," says Esther Tambe, MS, RD, CDN, CDCES, owner and founder of Esther Tambe Nutrition. One of those things is hydration.

Considering that more than 10% of the U.S. population is living with diabetes and 38% of those 18 and older have prediabetes, per the Centers for Disease Control and Prevention (CDC), it's important to consider different ways to support blood sugar regulation. We spoke with two registered dietitians who are Certified Diabetes Care and Education Specialists (CDCES) about the link between dehydration and high blood sugar.

What's the link between dehydration and blood sugar?

Dehydration is a risk factor for hyperglycemia, especially among those living with diabetes. There are a couple of reasons for this: Dehydration makes your blood more concentrated, and it may alter hormones related to blood sugar control. Some research even suggests that over time, dehydration might increase your risk of developing diabetes in the first place, although more research is necessary to confirm this link.

Dehydration Increases Glucose Concentration in the Blood

Your blood sugar levels are essentially a measurement of glucose concentration in your blood, according to the National Institutes of Health (NIH). It becomes elevated in those experiencing diabetes because insulin, the hormone that helps move glucose (sugar) from your blood to your cells, either isn't working properly or your body doesn't produce enough of it.

But let's get back to the H2O part: You've probably heard that your body is 50%–60% water. Well, some of that water makes up your blood volume. If you're dehydrated, your blood may become more concentrated since your body has less fluid to work with. As a result, your blood sugar levels can rise, says Tambe.

Dehydration May Impact Hormones Related to Glycemic Control

Besides insulin, other hormones may play a role in glycemic control. StatPearls notes that vasopressin is a hormone known for its role in regulating blood pressure and osmotic balance. Its secretion is impacted by hydration status. For example, a study in Diabetes Care found that vasopressin may also play a role in blood sugar regulation.

Furthermore, a 2017 trial in Nutrition Research found that individuals with type 2 diabetes who didn't drink enough water for just three days had worse results on an oral glucose tolerance test than those who were well hydrated. The researchers noted that this was mediated in part by the stress hormone cortisol. It can cause glucose to be released into the bloodstream, leading to high blood sugar levels.

Interestingly, a 2019 study in the Journal of Applied Physiology found that in healthy adults without diabetes, acute dehydration didn't alter blood sugar regulation as measured via an oral glucose tolerance test. It did cause copeptin levels—an indirect measure of vasopressin—to rise, though.

Those with Diabetes May Have Higher Fluid Needs

Frequent urination can be a symptom of hyperglycemia, per the NIH, which may lead to a vicious cycle of further dehydration in those with diabetes. A 2018 study in the Annals of Nutrition and Metabolism that assessed hydration during physical activity among people with type 1 diabetes found that participants still felt thirsty after drinking sufficient water according to sport nutrition guidelines. This makes sense, since increased thirst is another sign of hyperglycemia. The authors noted that while it's unclear why those with type 1 diabetes have higher fluid needs than those without the condition, one explanation is that excess urination could lead to greater fluid loss.

How Dehydration May Increase Diabetes Risk

While there isn't much research on this subject, the same study referenced above in Diabetes Care found a link between lower water intake—particularly among those drinking less than 0.5 liters per day—and greater new-onset hyperglycemia (high blood sugar). The study was observational, meaning it couldn't establish that the dehydration caused the hyperglycemia, but it did show a significant link between the two.

People Without Diabetes May Not Notice Hyperglycemia

Tambe and Diana Mesa RD, LDN, CDCES, founder and owner of En La Mesa Nutrition, say that dehydration can temporarily raise blood sugar in those without diabetes, too. Plus, the CDC estimates that 23% of those living with diabetes are undiagnosed. People who have been diagnosed with diabetes are typically accustomed to checking their blood sugar and noticing signs of hyper- or hypoglycemia. For those without a diabetes diagnosis, this may not be top of mind.

Also, dehydration and hyperglycemia largely overlap, so it may be tough to determine what's causing your symptoms. Common symptoms of dehydration include thirst, fatigue, dizziness, dry mouth, less frequent urination, dark-colored urine and dry skin. Symptoms of hyperglycemia include feeling thirsty, tired or weak, headaches, urinating often and blurred vision, per the NIH. Notice that most of the symptoms overlap; the biggest difference is that dehydration reduces urine frequency, while hyperglycemia increases it.

How to Stay Hydrated to Prevent High Blood Sugar

Staying hydrated is important for blood sugar regulation, but you may struggle to get enough fluids in. If you have a job that hinders you from hydrating during the day or you don't like plain water, you may need to get creative! Here are some ideas for staying hydrated to promote blood sugar control:

• Carry a reusable water bottle with you wherever you go. Increasing your access to water might increase your water intake. Make sure you like the bottle you use! Consider whether you like having a straw, wide-mouthed opening, and what size bottle works best for you so you're more likely to enjoy using it.
• Add flavor or bubbles to your water. If you get bored of plain water, try plain or flavored seltzer water. You can also try adding berries, lemon or cucumber to your water to give it a little flavor. For example, you can try our Lemon, Cucumber & Mint Infused Water.
• Set hydration goals that work with your schedule. If you know you struggle to drink water during the workday, consider adding a glass of water to each meal and snack. Also, make sure to hydrate whenever you do physical activity. Build these kinds of hydration check-ins into your day at times that make sense with your life, especially if your hydration windows are limited.
• Drink less sugar-sweetened beverages, not because they're bad for you, but because hydrating with regular water will help flush out the excess sugar that increases your blood sugar, says Tambe.

Frequently Asked Questions

Does blood sugar go up or down when dehydrated?

When you're dehydrated, your blood sugar typically goes up because your blood will be more concentrated. Therefore, the concentration of sugar relative to the volume of your blood will be higher.

Does drinking water help lower blood sugar?

Since dehydration can cause high blood sugar, drinking water can certainly help lower blood sugar if you're dehydrated. If you have diabetes, there are other factors that lead to high blood sugar, so you'll also need to consider your food choices, exercise habits, and doctor-recommended medications to help manage your blood sugar.

Can symptoms of dehydration be confused with high blood sugar?

Dehydration and high blood sugar have many symptoms in common, including thirst, feelings of tiredness or weakness, headaches and blurred vision, per the NIH. Mesa says that they can also both impact your mood and cognitive function, which can further hinder you from practicing health-promoting behaviors. However, high blood sugar levels can also lead to frequent urination, whereas dehydration does the opposite.

Bottom Line

Not drinking enough throughout the day could hinder glycemic control, particularly for those living with diabetes. Dehydration and hyperglycemia share many symptoms in common, so it can be easy to mistake one for another. To tell them apart, pay attention to your urine frequency; hyperglycemia usually leads to frequent urination while dehydration reduces urination. Be sure to keep a water bottle by your side and find creative ways to make getting the fluids you need fun for you so you can promote your overall health, including blood sugar regulation.