'Coffee doesn't affect your sleep? That's not a good sign,' says doctor

By KTimes

Korea remains one of the most sleep-deprived societies in the world as four out of 10 Koreans experience sleep disorders and the country's average sleep duration ranking near the bottom among major nations.

Sleep deprivation is not just a personal issue but a major public health problem that must be addressed collectively, Shin Won-chul, a neurologist at Kyung Hee University Hospital in Gangdong, Seoul, said in a recent interview.

“People say, ‘You’ll sleep forever when you die, so why sleep now?’ That shows just how lightly Korean society treats sleep,” said Shin, who is also president of the Korean Society of Sleep Research (KSSM).

According to a 224 KSSM report on sleep habits, Koreans sleep for an average of six hours and 58 minutes, which is 18 percent less than the OECD average. Sleep quality also ranks among the worst globally.

A February report by IKEA on global sleep habits ranked Korea 50th out of 57 countries with a sleep quality score of just 59. Only 17 percent of Korean respondents rated their sleep quality positively, the lowest rate among all countries surveyed.

The World Health Organization has labeled insomnia “the epidemic of industrialized nations.”

“Modern conveniences that are supposed to make life easier are instead eating away at our sleep," Shin said. He pointed to caffeine, blue light exposure, stress and psychological anxiety as key culprits behind Korea’s poor sleep.

“People who say coffee doesn’t impact their sleep are actually showing signs of exhaustion,” Shin said. “It means their brains are already so saturated with adenosine — a chemical that causes drowsiness — that caffeine has no more room to bind. So they may not feel more alert, but when they do sleep, the caffeine still interferes with deep rest.”

Adenosine triggers fatigue and sleepiness. Caffeine, which has a similar structure, blocks it from binding to receptors in the brain. The half-life of caffeine is about six hours, and it can take more than 10 hours to fully leave the body. Shin advises avoiding coffee in the late afternoon if restful sleep is the goal.

Alcohol may relax the body and bring on drowsiness, but that’s where the benefits end. Once ingested, alcohol is broken down into acetaldehyde and then into acetate, which stimulates wakefulness. “Plus, alcohol has a diuretic effect, increasing the likelihood of waking up in the middle of the night,” said Shin. “It completely disrupts your sleep structure.”

Melatonin hype? Don’t expect miracles

With widespread concerns over traditional sleeping pills, many turn to over-the-counter “sleep aids,” a term Shin says is not medically recognized. “Most so-called sleep aids are just antihistamines, which suppress histamine, the hormone that keeps you awake. It’s no different from actual sleeping pills.”

Melatonin, often marketed as a natural sleep solution, has surged in popularity. “It’s being advertised as the answer to all sleep problems, but its actual effect is relatively small,” Shin said.

Before bed, avoid screens

“Our body’s internal clock is designed to wind down when it gets dark,” Shin said. “But if you lie in bed and stare at your phone, the blue light activates melanopsin in your retina, which resets your biological clock and keeps you awake.” Moreover, engaging with stimulating content releases dopamine, a wakefulness hormone, further disrupting sleep.

Shin emphasized that many people blame liver function for persistent fatigue when in reality, poor sleep is the root issue. “If you think you can fix your exhaustion with medication while ignoring your lack of sleep, you’re missing the point,” he said.

Deep sleep isn’t just rest — it’s repair

During deep sleep, brain waves slow to 1 to 4 hertz, meaning the brain is nearly at rest. This is when the body begins to flush out toxins that have accumulated during waking hours.

“The blood vessels in the brain slightly loosen, allowing plasma to wash away inflammatory waste,” Shin said. “Without sleep, that ‘cleaning’ can’t happen, and those toxins pile up, leading to illness.”

Lack of sleep, especially less than six hours a night, increases the risk of coronary artery disease by 48 percent and stroke by 15 percent. It can also impair attention, memory and emotional health, contributing to anxiety and depression.

Shin warns that sleep deprivation must be recognized as a serious health issue with broad social consequences. “When people are chronically tired, we see more traffic accidents, workplace injuries and reduced productivity, not only for office workers but also for students.”

The estimated economic loss due to sleep deprivation in Korea is around 11 trillion won ($8.2 billion) per year.

This article from the Hankook Ilbo, the sister publication of The Korea Times, is translated by generative AI and edited by The Korea Times.