Temperatures approaching 40 degrees Celsius and weeks of tropical nights have gripped the country. A prolonged heat wave can be life-threatening for vulnerable groups — including children, the elderly and people with chronic underlying conditions — who face heightened risks of heat-related illness and dehydration. Patients with chronic conditions such as hypertension and diabetes need to be particularly careful, as heat can cause blood pressure and blood sugar levels to fluctuate far more than usual. Dehydration does not merely cause thirst; it can also trigger dizziness, falls and an increased risk of cardiovascular and cerebrovascular disease.
Dehydration is the greatest threat facing hypertension patients during a heat wave. When the body loses too much fluid, blood pressure drops and blood flow to the brain decreases, which can cause dizziness or loss of consciousness. Standing up suddenly from a seated or lying position raises the risk of orthostatic hypotension and fainting, and a resulting fall can quickly turn into a serious injury.
Many people assume that heavy sweating means they need to replenish salt as well as water — but this is a common misconception. Because sweat contains a lower concentration of salt than blood, heavy sweating actually concentrates the salt remaining in the bloodstream. Drinking water frequently and in sufficient quantities is therefore more effective at preventing dehydration than increasing salt intake. People should also avoid reaching for high-sodium foods such as naengmyeon broth when thirsty, as broth-based dishes are high in salt and can actually raise blood pressure.
Lee Hae-young, a professor in the cardiology department at Seoul National University Hospital, urged patients not to reduce or stop their medication on their own if their blood pressure reads lower than usual in summer. "First try drinking enough fluids, and if your blood pressure remains low even after that, the safest course is to consult your doctor and discuss adjusting your medication together," he said.
Heat waves affect not only blood pressure but also blood sugar. When blood volume is already reduced by sweating, diarrhea, alcohol consumption or caffeine intake can compound the risk of dehydration further, causing the blood to thicken and raising the risk of cardiovascular and cerebrovascular disease. Prolonged outdoor activity and work in hot, enclosed spaces should be avoided as much as possible.
For people taking antihypertensive medication, dehydration on top of the heat can trigger low blood pressure or dizziness. Anyone who feels dizzy when standing up, notices their blood pressure is significantly lower than usual, or experiences severe palpitations or fainting should consult their doctor rather than adjusting their medication on their own. Diuretics increase urine output to control blood pressure, which carries a risk of dehydration and electrolyte imbalance. SGLT2 inhibitors, a class of diabetes medication, cause fluid loss as they excrete glucose through urine, so patients taking them need to pay extra attention to hydration during summer.
Regular meals are just as important as adequate hydration. Skipping meals because of a poor appetite in the heat can impair the body's ability to maintain fluid balance. Older adults in particular may find that missing meals sap their energy and weaken digestion, leading to loose stools more frequently — which in turn raises the risk of dehydration. When digestion is poor, appropriate medication such as prokinetics can help.
Meals should center on easily digestible proteins such as white fish and lean meat, while fatty foods and excessive alcohol should be limited. However, some people taking antihypertensive medication should be careful not to consume too much fruit and vegetables, as doing so can raise potassium levels.
Managing daily activity and the indoor environment is equally important alongside diet. During a heat wave, reducing aerobic exercise by 20 to 30 percent compared with normal and getting sufficient rest is advisable. Indoors, maintaining a comfortable temperature and humidity through adequate air conditioning helps reduce the strain on the heart and blood vessels.
Park Min-sun, a professor in the family medicine department at Seoul National University Hospital, stressed that patients should not stop or reduce their blood pressure or diabetes medication on their own just because their readings are lower in summer. "Record your blood pressure and symptoms together, then consult your doctor to adjust your treatment in a way that suits your individual condition — that is the safest approach," she said.
Most heat-related illnesses improve with rest in a cool place and adequate fluid intake. However, failing to respond appropriately can allow the condition to progress to heatstroke, which can be life-threatening, making it critical not to miss the early warning signs.
If a person's body temperature exceeds 40 degrees Celsius and they begin to stagger from loss of coordination, or show unusual behavior or aggression, heatstroke should be suspected even if they have not lost consciousness. Medical attention should also be sought without delay when symptoms such as persistent headache, dizziness, nausea or vomiting, severe muscle cramps, a rapid heartbeat or difficulty breathing appear.
The sudden temperature change encountered when moving from outdoors to an air-conditioned interior is another factor to watch. A sharp drop in temperature affects the peripheral blood vessels and autonomic nervous system, placing significant stress on the cardiovascular system. On days when the temperature reaches 35 degrees Celsius or above, a fan alone is generally not enough to protect high-risk groups such as the elderly from heat-related illness. Rather than enduring the heat, people should make active use of air conditioning to keep indoor temperatures within a safe range.
Kim Tae-gyun, a professor in the emergency medicine department at Seoul National University Hospital, said that anyone whose body temperature exceeds 40 degrees Celsius and who shows abnormal behavior or altered consciousness should immediately seek medical care with heatstroke in mind. "During a heat wave, preventing dehydration through adequate fluid intake and rest is essential, and it is above all important never to dismiss the warning signals your body sends," he said.
kty@heraldcorp.com
