Heat is generated within the body through the metabolism of nutrients, such as the process of converting sugar to energy. Like all warm-blooded creatures, the human body tries to maintain a core temperature of 37 degrees Celsius (98.6 degrees Fahrenheit). When the air temperature rises, the body doesn’t have the option of generating less heat. So, for the body to maintain its core temperature, this extra heat – together with that generated through the metabolic process – must be lost through the evaporation of sweat.
According to the 2013 Canadian Diabetes Association clinical practice guidelines, metabolic, cardiovascular and neurological dysfunctions associated with diabetes, along with associated health issues and advanced age, reduce the body's ability to detect and then dissipate excess heat. Reductions in sweating and skin blood flow also decrease the body's ability to maintain its core temperature at safe levels, especially during extended heat exposure and/or while exercising in the heat.
Heat can beat the heart
Summer exercise safety is particularly important if you have been diagnosed with a heart condition. Damage from a heart attack can keep the heart from pumping enough blood to get rid of heat. The body can become overheated, so people with heart failure are more likely to develop symptoms of heat exhaustion. The combination of increased blood flow to the skin and dehydration may also cause blood pressure to drop low enough to cause dizziness or even falls.
Medications used by patients with heart disease may also interfere with the body’s heat regulation. Beta blockers slow the heartbeat, thereby limiting the heart’s ability to circulate blood fast enough for effective heat exchange. Diuretics (i.e. water pills) aggravate dehydration by increasing urine output. Other chronic conditions in people with diabetes, such as stroke, Parkinson’s disease or Alzheimer’s disease, can dull the brain’s response to dehydration, so it may fail to send thirst signals.
Some clinical studies have shown that air pollution or smog can trigger a heart attack, stroke or irregular heart rhythm – especially in people who are already at risk for these conditions. A recent 2008 analysis by the Canadian Medical Association estimated that some 21,000 deaths per year in Canada were associated with air pollution. Heart disease and stroke are the leading causes of death and disability among people with type 2 diabetes.
Beat the heat
Here are some tips for making sure your body temperatures stay in the normal range:
- Check the humidex score. Environment Canada issues a humidex (short for “humidity index”) advisory when the temperature is expected to be higher than 30°C and the humidex is expected to be higher than 40°C. The higher the humidex, the harder it is for sweat to evaporate and cool the body. You can learn more about the Canadian humidex calculator here
- Check smog alerts. Get up-to-date information about your local air quality. Sometimes, you can tell that the air is polluted – for example, on a smoggy or hazy day – but often you can’t actually see the pollution. In many areas, you can find air quality forecasts and reports on local television or radio stations, or in the newspaper. These reports use the air quality index (or AQI), a simple colour scale, to tell you how clean or polluted the air is. If you live in Ontario, you can sign up for email notifications here . This free service will alert you when your local air quality reaches levels of concern, and can help you plan your daily activities.
- Drink to your health. The lower your coolant level, the greater your chances of overheating. Unfortunately, staying hydrated isn’t always easy. Stomach or bowel problems, the use of diuretics, a faulty thirst signal, or low fluid intake can all interfere with a person’s ability to know when they’re dehydrated. On dangerously hot and humid days, drink plenty of fluid (just short of feeling bloated) 30 minutes before exercise, and drink at least 8 ounces of fluid after approximately every 20 minutes of exercise. After exercise, drink enough fluid to feel as if you have more than quenched your thirst (if you have congestive heart failure, check with your doctor or nurse first about how much fluid is safe for you to drink while exercising). Try to avoid sugary sodas and full-strength fruit juices, as they slow the passage of water from the digestive system to the bloodstream. As well, caffeinated beverages and alcohol actually increase dehydration, so avoid them as thirst-quenchers.
- Eat lightly. Stick with smaller meals that don’t overload your stomach. Cold soups, salads and fresh fruits can satisfy your hunger and also provide your body with much-needed extra fluid.
- Go slow. Exercise intensity drives internal body temperatures more than anything else. Slowing down the pace will do more for you than drinking an extra glass of water. As well, exercise early in the morning, when it’s coolest, and wear minimal clothing.
- Be mindful of any new symptoms (for example, dizziness, angina, palpitations, weakness, or undue shortness of breath).
- Find your cool. If your house doesn’t have air conditioning, find air-conditioned place to exercise (e.g. walking), such as a shopping mall or community centre.
Be sure to enjoy the summer!
For more information about exercise safety during hot weather, read Managing the Heat Wave with Diabetes.