Extreme heat: Staying safe if you have health issues

It's only July, yet crushing heat waves have hovered over parts of the US this summer. And dangerous, sometimes deadly heat waves are increasingly common around the globe.

Heat combined with humidity –– or high temperatures alone –– can make it difficult for your body to cool off sufficiently, especially if you have a chronic health condition such as asthma, heart disease, or diabetes. Here's what you need to know.

Which health conditions require special attention when heat rises?

Most of us know someone who is at risk from too much heat. Older people, and anyone taking medicine that affects the body's ability to hold onto water, such as diuretics, may be more vulnerable to heat illness. If you have any of the following conditions, it's important to be cautious during days when the heat index is high.

• Heart disease: Heat may increase the chances of heart attacks, heart arrhythmias, and heart failure.
• Asthma: Anyone with asthma, especially children, may find it more difficult to breathe on hot days. Some evidence suggests that inhalers stored in extreme heat may not work as well, possibly dispensing less than a full dose of medication.
• Lung conditions: Heat can irritate the lungs, causing flare-ups for adults who smoke, or have asthma or chronic obstructive pulmonary disease (COPD) — even for those spending most of their time indoors. Heat also increases ozone air pollution and the risk of dehydration, both of which can make breathing more difficult.
• Mental health: There's strong evidence of more instances of suicide, homicide, and violent crime on extremely hot days. Heat may also influence symptom severity in people with mood disorders and schizophrenia.
• Diabetes: People who have type 1 or type 2 diabetes have a harder time regulating body temperature and blood glucose when it gets hot out. Extreme heat can also damage insulin, insulin pumps, and glucose monitors.
• Pregnancy: Higher temperatures and air pollution may increase the risk that a baby is born too early or with a low birthweight.

How else does extreme heat affect the body?

Anyone can experience an imbalance  of essential minerals in the blood known as electrolytes during periods of extreme heat. But this is especially true for people with diabetes, heart disease or abnormal kidney function. When this occurs, a person may feel fatigue, nausea, or a headache.

In extreme instances, heart attack, irregular heart rhythms (arrhythmia), or problems with other organs may occur. Data from millions of people enrolled in Medicare show that hospital admissions during heat waves lasting two or more days are most often due to heat stroke, sunstroke, fluid and electrolyte imbalances, and acute kidney failure. Among older adults, heightened risk for hospital admission lasted up to five days after the hottest day.

Put a cooling plan into action

Keep it simple: learn how to avoid, spot, and treat heat-related illness, the Centers for Disease Control and Prevention advises. Right now, we do not have sufficient evidence to recommend actions like changing medication regimens, or staying indoors at one temperature and not others. Talk to your doctor about your situation, and take steps to take control of your health when it's hot outside.

• Have a plan in place for staying cool at home or going to a neighborhood cooling center. Don't wait for a heat alert before taking action if you have a chronic health problem or take multiple medicines. Your personal risk of getting sick from the heat may increase at temperatures below when heat alerts are often called, or sometimes when heat alerts aren't called at all.
• Check a weather forecast first thing in the morning and pay attention to days that are hotter than usual for where you live — and especially to how being outside on those days may affect your health. The New York Times maps dangerous heat zones and offers a heat index forecast for major cities and locales across the US.
• If your symptoms are already flaring on days when it will be hot outside, you'll need to be more cautious about going out. If you do go outside, try to stay in the shade. Stay alert to how you're feeling and find a cool place inside if you feel symptoms arise.
• Stay hydrated by drinking water and drinks that replenish electrolytes. Some sports drinks have electrolytes but may have lots of sugar. That can be a problem for people with diabetes, so read labels carefully.

The bottom line

Climate change makes it likely we will experience longer and hotter heat waves. If you have existing health conditions, take steps now to protect your health. Talk to your doctor about how heat might affect you, and decide on a plan to help you stay cool. Staying informed and attuned to any symptoms you experience will help.

Harvard Health Publishing would like to acknowledge Aaron Bernstein, MD, MPH, who wrote the original version of this post.