How many hours should a 21-year-old sleep each day?

Generally, it is appropriate for 21-year-olds to sleep 7–9 hours per day. During periods of heavy academic or work demands, sleep may be reduced to 6 hours temporarily. However, consistently sleeping less than 6 hours or more than 10 hours can negatively affect health. If concerns arise, it's advisable to adjust based on individual physical and mental conditions. Detailed analysis is as follows:

At age 21, individuals are in a stage of physical development and peak energy levels. Seven to nine hours of sleep adequately meet the brain’s need for rest and the body’s need for recovery, support memory consolidation and immune function, and help maintain focus and efficiency during daily study or work, reducing fatigue and problems with concentration.

If special circumstances such as exam preparation or overtime work require it, sleeping around 6 hours per day for a short period can be temporarily tolerated, but this should not extend beyond three consecutive days. Chronic sleep deprivation may lead to endocrine disorders, mood swings, and even impair vision and digestive function. Sleeping more than 10 hours per day may result in lethargy, disrupted circadian rhythms, and reduced daytime productivity.

To promote healthy sleep, maintain a regular schedule by going to bed and waking up at consistent times. Create a quiet and comfortable sleep environment, and avoid behaviors such as using smartphones or staying up late before bedtime. If insomnia persists or you continue feeling fatigued after sleep, consider adjusting lifestyle habits or seek professional medical assistance promptly.