Super hot, sticky days can be unpleasant for anyone. But for those with certain health conditions, they can pose a more serious threat.
Several studies show that people with chronic diseases — for instance, cardiovascular, respiratory, metabolic and neurological conditions — are more likely to visit the emergency department or die during a heat wave.
In some cases, that’s because people with underlying health conditions may be more susceptible to heat exhaustion or heatstroke because certain body systems such as the heart, kidneys and nerves are not functioning optimally, said Robert Meade, a research fellow at the Harvard T.H. Chan School of Public Health who studies the effect of heat on vulnerable groups.
But a bout of heat can also lead to flare-ups or exacerbate existing symptoms even if you’re nowhere near overheating, Meade said. He offered a swimming analogy: If your body is operating as if you are treading water, the heat is like someone handing you a brick. Now, each system is working harder to stay afloat, which can trigger a health condition in ways that range from miserable to potentially life-threatening.
We asked experts about the conditions that research suggests are most commonly or severely aggravated by heat, and how to manage flare-ups this summer.
Arthritis
Research on osteoarthritis (a breakdown of joint cartilage due to wear and tear) and gout (a form of inflammatory arthritis that often starts with intense pain in a big toe) suggests that either temperature extreme may exacerbate symptoms. Heat, particularly when paired with humidity, may increase inflammation, resulting in more painful, swollen joints in people with arthritis, said Aerial Petty, medical director of primary care at Morris Heights Health Center in the Bronx.
Gout may worsen in the heat for a different reason: Dehydration allows for uric acid — a natural cellular waste product filtered out by the kidneys — to become concentrated in the blood and form more of the uric acid crystals in joints that cause gout pain.
Arthritis also can get worse with dampness, which can lead tissues inside joints to expand and press on nearby structures. A 2019 study showed that of various weather conditions, humidity had the greatest effect on pain severity in more than 2,000 people with chronic pain conditions, predominantly arthritis.
Kidney stones and kidney disease
Medical records suggest above-average temperatures are linked to a surge in kidney stone diagnoses, which has been mainly attributed to dehydration: A loss of fluid leaves urine more concentrated with minerals that can crystallize into stones. In those who are prone to them, the backup of minerals can clump onto existing bits, upping the chance that a tiny stone grows larger, dislodges and blocks the tube to the bladder — causing severe pain.
There’s also evidence that greater heat exposure is tied to more rapid decline in kidney function among people who have chronic kidney disease (CKD). The cooling mechanism that sends more blood to the skin during heat exposure leaves less available for internal organs, particularly the kidneys, Meade said. So if you’re someone with poor kidney function, the dip in blood supply (and oxygen) can push your kidneys into a “danger zone,” he said.
In people with CKD, the kidneys are also less adept at regulating fluid balance, said Lauren Siewny, medical director of the Duke University Hospital Emergency Department. So sweating could fast-track dehydration or, conversely, cause water retention — leading to a dangerous electrolyte imbalance.
Asthma and COPD
If you have asthma or chronic obstructive pulmonary disease (COPD), you might find that chilly air irritates your airways. But hot, humid air can be just as problematic for some people with these conditions. Studies have recorded a rise in related emergency room admissions, hospitalizations and exacerbations amid high heat.
Breathing hot air, whether it’s dry or humid, is thought to cause airways to narrow, increasing the risk of an asthma attack or COPD exacerbation.
Periods of high heat also tend to coincide with poor air quality, Siewny added. A combination of sunlight, heat and stagnant air facilitates an uptick in ground-level pollution, like ozone — and humidity creates the ideal environment for mold spores and dust mites to multiply. All of the above can irritate the respiratory tract and provoke a flare-up.
Lupus
Research on heat and autoimmune conditions is still in its early stages, but emerging evidence suggests that lupus, or systemic lupus erythematosus — a condition in which the immune system attacks healthy organs — may be particularly sensitive to heat.
A 2020 study found that rash-, joint- and blood-related flares of 1,200 lupus patients coincided with warmer days, and the incidence of joint flares also rose when it was more humid.
A possible mechanism is inflammation, which research suggests may increase throughout the body in high heat and humidity. In lupus patients, that may lead to more swelling and pain in the joints and worse fatigue, Petty said.
Many people with lupus also have increased sensitivity to sunlight, Petty added, where even a little exposure can cause rashes, making it especially crucial to be diligent about sun protection.
Diabetes
Hot days have been linked to an outsize number of hospital admissions for both Type 1 and Type 2 diabetes, and heat waves to a rise in diabetic morbidity and mortality risk.
Heat can make blood-sugar control challenging because it can lead to swings in both directions, Siewny said. On the one hand, faster circulation and dilated blood vessels could speed up insulin absorption, causing low blood sugar. On the other hand, dehydration could concentrate sugar in the blood, causing high blood sugar.
Because of the added unpredictability, Siewny said it’s essential for people with diabetes to check their blood sugar more frequently as temperatures rise.
Multiple sclerosis
It has long been established that in people with multiple sclerosis — a disorder in which the immune system destroys the protective myelin sheath coating nerve fibers,an elevation in core body temperature due to exercise can flare symptoms. And recent research has shown that this heat sensitivity, called Uhthoff’s phenomenon, often occurs in warmer weather, too.
The heat hinders electrical signals traveling along damaged nerves, which can lead to a surge in symptoms such as fatigue, muscle weakness, numbness and cognitive issues. This typically subsides when the body cools down and doesn’t reflect a true relapse of the condition.
Heart disease
In warm weather, your body sends extra blood to the vessels in your skin, which widen, letting heat escape and sweat evaporate. This process also requires the heart to pump harder, Meade said.
This can be problematic for someone with coronary artery disease, which occurs when plaque clogs the arteries that supply blood to the heart. “You can develop a mismatch between what the heart needs when it’s working harder to face the heat and what the body is able to deliver,” Siewny said.
That raises the risk of a heart attack or stroke — both of which rise in incidence during heat waves.
Those with heart failure, who often take diuretics (a.k.a. water pills) to manage fluid buildup, are at higher risk of dehydration in the heat. Paired with the added burden on the heart, this could trigger worsening heart failure or even kidney injury, Siewny said.
Migraine
While studies on temperature and migraine have yielded inconsistent results, research suggests that seasonal switches and swings in temperature and air pressure — in either direction — can trigger attacks, possibly because of how blood vessels and nerves adapt to those shifts.
Still, summer can pose a unique migraine threat — for instance, because of how heat increases ground-level smog (a trigger, in and of itself). The bright glare of sunlight can also spark an attack by activating the nerve involved in migraine pain. And then there’s the added risks of dehydration and sleep disruption, which can underlie flare-ups, too.
Depression and anxiety
Hot days bring higher rates of mental health-related emergency department visits and even suicide, putting those with depression or anxiety at particular risk.
Because a vast array of factors can influence mood, several possible explanations exist. On the physiological front, activation of the body’s stress response amid heat may rev up anxiety. Psychologically, the feeling of being unable to control or escape the heat could play a role, Meade said. Heat waves can also bring sleep disruption, which is known to exacerbate depression and anxiety, said Lorenzo Norris, associate professor of psychiatry and behavioral health at the George Washington University School of Medicine and Health Sciences.
Additionally, people who take antidepressants, like selective serotonin reuptake inhibitors, may be more susceptible to dehydration and overheating, as these drugs disrupt temperature regulation, Norris added.
How to manage symptoms in the summer
Typical stay-cool measures apply all the more for people with chronic conditions. Stay hydrated. Run the air conditioning at home, if you have it, or use fans or water spray bottles, Meade said. Petty also suggested carrying a handheld fan while outside, wrapping a cool rag around your neck, and wearing breathable clothing.
It’s also wise to book an appointment with your doctor now, in anticipation of a potential flare-up, particularly if you haven’t seen them in a while. This way, you can game-plan for a heat wave and review your medications, as certain ones may work differently in the heat, Meade said.
Also, avoid other triggers that may be more in your control — like missing meals or getting too little sleep — so they don’t pile up, Petty said.
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