Due to the demands of modern life, many people believe that sleeping only 5–6 hours a night is enough to maintain good health. However, science shows that this is not an optimal amount of sleep—and it may even be dangerous if sustained over time.

Adults should ideally sleep between 7 to 9 hours per night. This is the amount of sleep that best supports both physical and mental well-being. When the body only gets 5 to 6 hours of sleep a day, several physiological and psychological functions can become impaired—ranging from memory and immunity to hormonal balance and life expectancy—according to the health site Medical News Today (UK).

If you consistently sleep only 5–6 hours a night, your body may undergo the following changes:

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Weakened Immune System

One of the most serious consequences of insufficient sleep is a weakened immune system. A study from the University of California, San Francisco (USA) found that people who sleep less than 6 hours per night are four times more likely to catch a cold compared to those who sleep 7 hours or more.

Deep sleep is when the body produces cytokines—molecules that help fight inflammation and respond to viruses and bacteria. Lack of sleep lowers cytokine levels, slowing the immune response. As a result, the body becomes more prone to illness and takes longer to recover.

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Reduced Life Expectancy

Research published in the Journal of Sleep Research shows that long-term sleep deprivation (less than 6 hours per night) increases the risk of early death, especially from cardiovascular disease, diabetes, obesity, and cancer.

Inadequate sleep affects the regulation of insulin, cortisol (stress hormone), and blood pressure. Another study in the European Heart Journal found that people sleeping fewer than 6 hours had a 48% higher risk of heart disease and a 15% higher risk of stroke compared to those who sleep 7–8 hours.

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Higher Risk of Accidents

Sleep deprivation can be just as dangerous as drinking alcohol when it comes to driving. Surveys show that people who sleep only 5–6 hours per night are twice as likely to be involved in traffic accidents as those who sleep 7–9 hours.

The reason is that lack of sleep leads to slower reflexes, reduced concentration, and daytime drowsiness, all of which increase the likelihood of mistakes at work, behind the wheel, and even serious workplace accidents.

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Visible Physical Signs

We may try to mask fatigue with coffee or makeup, but the body always finds a way to signal distress. According to Medical News Today, signs such as puffy eyes, dark circles, dull skin, and premature wrinkles often appear with prolonged sleep deprivation.