Even though most adults need 7-9 hours of sleep in a 24-hour day, exactly when our bodies naturally tend to fall asleep and wake up each day can vary. Scientists believe that people have inherent differences in when they sleep and wake best. This natural pattern is a chronotype. Whether you’re a night owl (an evening person), or a lark (morning person) is partly determined by your genetics.
If you know your natural tendency it might help you understand how you adjust to a particular shift schedule. For example, if you’ve always been a night person and feel most productive in the evening hours, an evening shift might work best for you, because your circadian rhythm allows you to be alert in those hours. If you’ve always woken up early and felt sharp and energetic in the morning, a night shift may be particularly hard for you. Some people fall in the middle of the two tendencies. If you don’t have a strong day or night tendency (and your employer is flexible) you may try different shift hours to see which fits best for you.
Certain people are also more affected by schedule changes overall—their internal clock has a harder time adjusting, and changes in sleep hit them harder than others. These people should be diligent about protecting their sleep time if they are working night or rotating shifts.
Source: National Sleep Foundation