More than 18,000 people died from sudden cardiac arrest without previous symptoms or warning signs in 2017 -- making it a bigger cause of death than lung cancer, at 17,980, and road traffic accidents, which killed 5,028 in the same year.

According to data released by the Korea Centers for Disease Control Wednesday, 25,859 people died from sudden cardiac arrest in 2017. Excluding accidental and suicidal deaths, 18,261 died without warning.

Ministry of Health and Welfare’s statistics show that on average, about 300 more die per month from sudden cardiac arrest in winter than summer.

To avoid unexpected heart problems, cardiologists advise against physical activity early in the morning when temperatures are low.

“Low ambient temperatures cause blood vessels to contract, and when coronary arteries narrow, the blood supply to the heart can be interrupted,” said Park Dug-woo, a heart specialist at Asan Medical Center. “Blood clots are also more likely to form in the morning.”

Sudden cardiac arrest may be preceded by symptoms about an hour earlier. Warning signs include chest pain and discomfort, shortness of breath, nausea, lightheadedness, and palpitations. Should these symptoms appear, an immediate medical response should follow, experts said, ideally within an hour.

“Regular checkups and calling the ambulance without hesitation in case of any discomfort are two simple ways,” Park added.

High blood pressure, diabetes, obesity also accompany high risk of cardiac disorder.

By Kim Arin (arin@heraldcorp.com)