The downside of a bad night's sleep is that it doesn't just make you lethargic. We doctors have a reverse thinking, that is, in all things, without which, life will be the fastest to the end, it is the most important for health. Skipping exercise, fasting, or poor mindset won’t cause immediate harm. After counting down, there are only three things you can't do without: hydration, exercise, and sleep.

If you don't hydrate at all, you will die soon, but considering that our food contains more or less water, extreme dehydration is rare daily. Similarly, if a person does not exercise at all and lies still in bed, muscle atrophy will occur, but such an extreme case hardly exists. We get up to go to the toilet, walk to the office next door, go downstairs to eat, and so on, and there is more or less an element of exercise.

However, sleep is simply sleep. According to the medical profession, sleep is a pillar of human health and plays a vital role in maintaining our physical health, mental balance, cognitive ability, and emotional regulation. Sleep is one of our daily behaviors for which there is no alternative and which needs to be taken seriously.

Unfortunately, poor sleep has become increasingly common among us.

Heart disease and stroke have always been caused by lifestyle. In the past, heart disease clinics were filled with obese individuals with poor dietary habits, but in the last 10 years, I've seen fewer and fewer fat people, but nearly 70% of my patients have sleep problems. Sleep disorders now top lifestyle factors in cardiac patients.

There are many reasons for poor sleep, so we don't have to be too hard on ourselves and demand infant-level sleep quality. In this talk, I will rely on a lot of research to find the bottom line and ceiling of sleep with you. The bottom line is the lower limit that we can't break through, and the ceiling is what we should sleep like to achieve the best sleep. As long as your sleep is within this range and meets your needs, it's fine.

I will give you three elements of sleep, namely: sleep duration, sleep/wake timing, and sleep environment.

Optimal Sleep: 7-8 Hours

Firstly, how long should we sleep? This is one of the key factors affecting the quality of sleep. Let's start with the bottom line. The conclusion is not so strict, but there is a reasonable range between 6-8 hours. Avoid sleeping less than 5 hours or exceeding 9 hours. Sleeping less is not good, but what does it matter if you sleep more? Let's look at the literature.

A study based on a 9-year follow-up of 400,000 people with chronic diseases in China found that compared with people who slept 7-8 hours a day, those who slept less than 5 hours a day had a 10% increase in stroke and a 19% increase in cerebral hemorrhage; while those who slept more than 10 hours a day had similar risk elevations, with stroke increasing by 12% and cerebral hemorrhage increasing by 23%; individuals sleeping under 5 hours or over 10 hours daily faced 23% higher cardiovascular risks.

Sleep and Wake Timing

The second question is what time you go to bed and what time you get up. Does this matter? Yes, it does. Adjusting it well will greatly improve your sleep efficiency. Just like, the same is about 7 hours of sleep a day, but you adjust this time, you get a plus point, outperforming others who also sleep 7 hours daily.

Why is it important to sleep and wake up at the same time? The principle is that the human biological clock is affected by natural light, consistent bedtime, adequate duration, and circadian rhythm alignment are critical.

In November 2021, the University of Oxford published a study in the Journal of the European Society of Cardiology showing that 10:00-10:59 pm is the prime time for the human body to naturally enter the sleep state. In this period sleep helps to significantly reduce the risk of cardiovascular disease, promote rapid deep sleep entry, promote body repair and metabolism, enhance immunity, prevention of chronic diseases.

According to the optimal sleep time of about 7 hours, the best rhythm is to go to bed between 10-11 pm and get up between 6-7 am. You see, it's just enough to ensure that you get enough sleep and keep in sync with your natural biological clock.

Of course, some people say I'm too busy to go to bed at 10 o'clock, so what should I do? Don't worry. What I just said is the best option, not the bottom line. Compared to the very strict bottom line of sleep duration, current research has not found that specific sleep/wake times are inherently harmful. In other words, whether you choose to go to bed at 9.30 pm or stay up until 1 am or 2 am, as long as you get seven hours of sleep, the overall effect will not be too great.

However, there is also some evidence that sleeping late can affect metabolism. This is because our fat metabolism is most active in the late evening, which is also when the pancreatic function is repaired. An experiment that included more than 13,000 subjects found that insulin resistance (HOMA-IR) increased by 1.3 percent after each additional hour of delayed sleep, and sleeping late has also been found to be associated with some early-onset coronary heart disease. Therefore, it is still recommended that you try not to stay up past midnight, and if you already have high blood sugar, high blood cholesterol, obesity, or a family history of diabetes in your home, staying up late is especially inappropriate for you.

Sleep Environment Considerations

Thirdly, you should also pay attention to the humidity. Whether you use electric blankets or not, humidity affects the quality of sleep and also affects the onset of some respiratory diseases. Ideal bedroom humidity is between 50-70%, achievable with a humidifier. Humidifier selection and usage guidelines, I will have a special talk later to tell you.