Does heat affect blood sugar? What if we told you that jumping into the pool on a hot, summer day could actually be beneficial for your blood sugar? No, cold water does not take excess sugar (glucose) out of your blood, but it does keep you cool, which reduces your risk of becoming dehydrated and ultimately keeps your blood glucose concentration better balanced. High summer temperatures and humidity levels, on the other hand, can lead to rising blood glucose levels. The effects of high heat are worsened if you’re exercising, as both blood sugar spikes and sharp drops can occur. And those with diabetes are affected by heat even more, and in several additional ways. Here’s what you need to know about heat, blood sugar and health this summer so you can better face the challenges that high temperatures pose. 

How does heat affect blood sugar?

The main concern with extreme heat relative to blood glucose is the risk of dehydration. When your body is dehydrated, you have less water in your blood, which means the concentration of glucose in your blood is stronger (even if the amount of glucose in your blood hasn’t ultimately changed). In other words, dehydration causes the ratio of blood glucose to water to rise, which increases your blood glucose level. Too much glucose in the blood (hyperglycemia) then overexerts your kidneys, which are responsible for filtering your blood and removing waste, leading to more frequent urination and more dehydration. It’s a vicious cycle.

Having diabetes already presupposes you to dehydration, but being in extreme heat with diabetes increases your risk of experiencing dehydration even more, potentially leading to dangerous blood glucose spikes. 

Physical activity in the heat complicates things

Normally, physical activity helps you better manage blood glucose levels. Research has concluded that consistent exercise can reduce the risk of developing type 2 diabetes (T2D) by up to 50% as insulin sensitivity and glycemic control are improved. 

During exercise, your muscle cells take in the excess glucose in your blood and use it for energy, effectively lowering your blood glucose. In particular, one study found that aerobic exercise (cardio), in comparison to resistance training, resulted in a larger mean glucose reduction (3.94±2.67 mmol/L or 70.92±48.06 mg/dL) during exercise in adults with type 1 diabetes. The blood-glucose-lowering effect of exercise, in general, makes your body less dependent on insulin to manage blood sugar. This improves your insulin sensitivity because your body uses insulin more effectively (you need less insulin to lower blood glucose). 

If physical activity can lower blood glucose levels, how can that be a bad thing? Physical activity in the heat is what complicates things. Heat (and dehydration) can raise your blood glucose levels, while physical activity will lower them. Being physically active in the heat puts you at risk of both high and low blood glucose. This is potentially dangerous for anyone, but particularly if you take insulin: your blood glucose levels might drop too low (hypoglycemia) during physical activity. Thus, you may or may not need to adjust your insulin dose for physical activity in the heat; double-check with your doctor for personalized instructions. 

There’s really no accurate way to predict how heat and physical activity might impact your blood glucose levels, other than to measure and monitor them closely with blood glucose monitoring devices. You should monitor your levels before and after physical activity, as well as during it if you plan to have a longer or more intense workout. If your level is below 100 mg/dL before your workout, you may need to grab a snack with fast-acting carbs so your blood glucose level doesn’t fall too low while you’re exercising. If your level is above 240 mg/dL before starting your workout, you might want to err on the side of caution: test your urine for ketones (suggestive of a lack of insulin in the body to regulate blood glucose). Exercising with high levels of ketones may induce ketoacidosis, which could be potentially fatal. When engaging in longer or more intense workouts, monitor your blood glucose level every thirty minutes to an hour. If your level falls below 70 mg/dL during exercise, take a break and grab a snack to raise your blood glucose to a safer level. 

All this data that you retrieve daily from your blood glucose monitors can be used intuitively using January AI’s app, which uses artificial intelligence (AI) to help you make better and more informed choices — such as when is the best time to exercise and what foods should you eat and avoid.  

Diabetes can affect your body’s ability to regulate temperature

Heat and diabetes don’t have the most healthy relationship. Diabetes often leads to nerve damage, which impacts the sweat glands and their ability to receive signals from your body to cool itself down when it’s too hot (through sweating). High blood glucose, together with high levels of fats (such as triglycerides), damages blood vessels that transport oxygen and nutrients throughout the body; and nerves don’t function properly without enough oxygen and nutrients. Permanently damaged nerves may bring about numbness or pain in certain parts of the body (such as the legs and feet), as well as an inability to regulate body temperature through sweating. 

When your body cannot cool itself down in the heat by sweating, your body is continuously hot, which can lead to dehydration and high blood glucose. When it’s humid outside, it’s even harder to regulate body temperature because the air around you feels so hot and your sweat does not evaporate quickly enough to cool you down. Extended periods of such conditions can result in heat exhaustion or a heat stroke. 

Sunburn can cause blood sugar to rise

Not only can heat affect blood glucose, but so too can getting sunburnt — in a subtle but sure way — raise blood glucose levels during the summertime. The pain from your sunburn causes stress to your body, and stress (in any form) negatively influences insulin absorption. A study of the correlation of job-related stress on cortisol (a hormone that regulates the body’s stress) and insulin resistance found that stress from demands at work and insecurity at work were linked to high cortisol levels and thus insulin resistance: “Cortisol [was] a positive predictor for insulin resistance.” Experiencing chronic stress impacts your body’s ability to use insulin effectively, which may cause blood glucose to rise.

In addition to insulin resistance, sunburn also causes your body to feel extra hot. Have you ever felt your skin after a sunburn? It almost feels like your skin is radiating heat — because it is. A sunburn means you’ve had too much radiation from the sun, and what heat is taken in must be radiated out. You feel the heat coming off of your body as a result. A sunburn makes it harder for you to regulate body temperature and, consequently, your blood glucose levels. 

Extreme heat can harm diabetic supplies and equipment

Not only does heat affect blood sugar, but it may also damage your diabetic supplies and equipment. Blood glucose monitors, insulin pumps and other diabetes equipment may work improperly when exposed to extreme heat. Insulin medication, when exposed to extreme temperatures, may lose effectiveness and become unusable. Here are some general guidelines for storing insulin supplies, provided by the Food and Drug Administration (FDA):

• Unopened insulin can be stored in the fridge at temperatures between 36°F-46°F.
• Vial or cartridge insulin (opened or unopened) remains usable for up to 28 days without refrigeration.
• Never freeze insulin and never use insulin that’s been frozen. Frozen insulin renders the insulin ineffective.
• Insulin pumps exposed to temperatures over 98.6°F should be discarded immediately.

Refer to this FDA page on insulin storage for more guidelines on storing insulin supplies. Also, double-check the instructions of your medication on how to properly store your diabetic supplies.  

Tips to stay cool and better manage blood sugar this summer

Extreme heat may make blood glucose control more difficult, but there are ways to work around it. Here are seven simple tips to help you stay cool and have a better grip on blood glucose control. 

1. Stay hydrated

Dehydration puts you at risk of high blood glucose. Make sure you are drinking plenty of water throughout the day, even if you don’t feel thirsty. The heat can quickly dehydrate you if you’re not paying close attention. 

2. Check your blood glucose before and after physical activity

Being active in the heat may make it difficult for you to gauge your general blood glucose levels. Skip the guessing and check your blood glucose before and after physical activity so you can take immediate and appropriate action if necessary. 

3. Stay in the shade and off of black-top concrete

Black-top concrete ground absorbs and retains the heat from the sun. If it’s extremely hot outside and you’re standing on top of the concrete ground, you can feel all the heat emanating from it. Walking on grass and in the shade can help keep you cooler. 

4. Bring a fan or mister

If you have damaged nerves due to diabetes, your ability to regulate body temperature may be impaired. You might not be able to cool down when it’s hot outside. Sidestep this by bringing a portable fan or mister with you to keep you cool. There are some devices that contain both in one.

5. Wear clothing that keeps you cool

During the summer, avoid wearing tight-fighting and dark-colored clothes, which retain heat. Opt for clothing that is lightweight, light-colored and breathable.

6. Wear sunscreen

Avoid getting sunburnt as that may raise your blood glucose level. Use sunscreen before, during and after physical activity in the sun to help protect your skin from sun damage, as well as to keep your body free from unnecessary stress.

7. Keep your diabetic supplies out of extreme heat

Avoid exposing your diabetic supplies and equipment to extreme heat. Keeping them in the glove compartment or in the trunk of your car on a sunny day can ruin your supplies. If you have to travel with your insulin, consider getting portable insulin coolers to keep your insulin at appropriate temperatures. 

Key takeaways

Does heat affect blood sugar? Yes, and in many ways. Heat causes dehydration which leads to high blood glucose, which then tends to result in more frequent urination, causing further dehydration — a vicious cycle. Paired with physical activity, heat may cause dramatic fluctuations in your blood glucose because heat raises that level while physical activity lowers it. Thus, monitoring your blood glucose levels before and after physical activity is crucial for safe blood glucose levels this summer. Heat also makes it hard for those with diabetes to stay cool due to nerve damage and an impaired ability to regulate body temperature, and high humidity or having a sunburn can magnify this problem. If you use insulin or diabetic equipment, make sure to keep these supplies out of extreme heat so they don’t lose effectiveness. All in all, the heat represents a multi-faceted health challenge. Fortunately, you can still enjoy your time outdoors this summer by taking the steps and precautions we’ve outlined in this report.