Management of diabetes in hot weather

Dr Louise Johnson educates us on how to manage glucose levels during hot weather.

Thermal stress in cold and hot weather

Having diabetes tends to place individuals at greater risk for heat-related illness during heat waves and extreme hot weather.

Diabetes has been linked to impairment in temperature regulation during extreme hot or cold weather. These circumstances are referred to as thermal stress. This can be challenging on the body: both on the heart and glucose control.

During intense hot weather, the blood vessels of the skin open-up (vasodilation) to help the body expel extra heat this way.

In cold weather, the opposite happens and the skin blood vessels close-up (vasoconstriction), thus sending all the blood to the core of the body. Warmth is preserved in this way.

Impaired temperature regulations

In people with Type 1 or Type 2 diabetes these mechanisms may be impaired. This can be due to:

  1. Long-standing diabetes with complications of peripheral neuropathy (loss of sensation in feet or lower sensation or burning feet).
  2. Complication of peripheral vascular disease (illness of blood vessels of legs that cause muscle cramps when walking a distance). These abnormalities affect the blood vessels and nerves of the legs more than the arms and cause an abnormal reduction in sweating.
  3. It is now thought that abnormal sweat glands and sweat response can also in itself be a complication of diabetes. It is proven that people with diabetes have less nerve density at the site of the sweat glands. The sweat glands also produce less sweat than healthy individuals.1
  4. Poorer glucose control with HbA1c above 8,5%.
  5. Longer duration of diabetes.

How the body regulates temperature

The body regulates a tight temperature control of 37 degree Celsius. Life-threatening complications can arise with a core temperature increase as small as three degrees (40 degrees).

To maintain this body temperature, the body must be able to sweat to cool down. This is particularly important during exercise in the heat. Sweat dripping promotes no heat loss but instead dehydration. To cool down, sweat must be able to evaporate.

High-risk of hospitalisation in hot weather

Epidemiological data shows that Type 2 diabetes patients have up to 56% greater risk for hospitalisation and mortality during a heat wave. This is because Type 2 diabetes presents a lot earlier with macro vascular (big blood vessels) disease, hypertension, obesity and abnormal blood lipids.2

It was also shown that young overweight individuals with a BMI above 27 (normal is 18 to 24) are 3,5 times more likely to experience a heat-related fatality compared to their lean counterparts. This is worse once diabetes is added to the equation.

It is well-established that glucose levels decrease in those with diabetes during an exercise bout. Hot conditions can also independently change glucose by increasing insulin absorption and cause lowering of blood glucose.

Local heating of the insulin injection site can lower glucose levels through faster insulin absorption.

Consistent with these findings, seasonal variations in glucoses control have been reported. It shows that HbA1c levels are clinically lower in spring and summer relative to autumn and winter. This is independent of exercise levels.

Severe hypoglycaemia (low blood glucose) is almost twice as frequent in the summer months. The difference in glycaemic control in the winter may be related to the stress hormone cortisol that causes a degree of insulin resistance.

How to manage glucose levels during warmer months

  1. Drink plenty of water even if you’re not thirsty. This will prevent dehydration. Dehydration can raise blood glucose and can cause excessive urination that can aggravate the dehydration.
  2. Avoid alcohol and drinks with caffeine (coffee and sports drinks). Drinking them can lead to water loss and spike blood glucose levels.
  3. Check blood glucose regularly before and after you are active.
  4. Don’t store insulin or oral diabetes medication in direct sunlight or in a hot car. If you’re travelling, keep insulin and other medication in a cooler bag. Remember not to put insulin directly on ice or a gel pack.
  5. Heat can damage your blood glucose monitor, insulin pump, sensor, and test strips. Don’t leave them in a hot car, by a pool, in direct sunlight or on the beach.
  6. Remember hot temperatures can change how your body uses insulin. You may need to test your blood glucose more often and adjust your insulin dose and what you eat or drink.
  7. Uses sunscreen to prevent sunburn. Sunburn is an inflammation of your skin and causes a rise in blood glucose. The same as what happens when you develop an infection.
  8. Keep items at hand to treat low blood glucose. This can be glucose tablets or gel. If you have frequent low blood glucose levels or aren’t aware of it, a glucagon injection kit should be taken with for an emergency. This should be administered by a friend when you’re unable to swallow glucose or in a coma.
  9. Keep snacks with you. This is important since it can serve as a meal replacement in emergency circumstances or if glucose is low.
  10. Limit how much time you spend outside in extreme temperatures. Remember it’s harder to stay cool when the humidity is high. Humidity above 40% in hot weather can be dangerous. It’s better to stay in the shade or inside.
  11. Remember your feet. Diabetes patients have a higher risk for feet problems (damaged nerves, abnormal blood flow, burning feet.) The summer is a great temptation to go bare feet on the beach or next to the pool. Be aware and check your feet daily at the end of a day for any trouble.

Enjoy summer

Summer is a wonderful time of year with lots of sunshine, long hot days and nice sundowners on the beach or next to the pool. Enjoy this time but remember to drink enough water and check your glucose.


  1. Kenny GP, Sigal RJ et. al. “Body temperature regulation in diabetes.” Temperatue Vol 3 ,1 p119-145; 2016
  2. Semenza JC, McCullough JE et. al. (1999) ‘Excess hospital admissions during July 1995 heat wave in Chicago.’ Am J Prev. Med. 16:269-77
Dr Louise Johnson


Dr Louise Johnson is a specialist physician passionate about diabetes and endocrinology. She enjoys helping people with diabetes live a full life with optimal quality. She is based in Pretoria in private practice.