Sleep Debt: Can You Carry Over Sleep From Yesterday?

Sleep is a complex and mysterious process that remains only partially understood by experts. While it is possible to make up for lost sleep, it doesn't work in the way we might think. You can't store sleep, and while naps can be refreshing, they do not replace a full night's sleep. However, research shows that afternoon naps, when timed correctly, do not negatively impact nighttime sleep. In fact, people who take afternoon naps obtain as much or more sleep in a 24-hour period than those who don't nap. That being said, it's important to prioritize consistent, quality sleep to avoid the negative consequences of sleep deprivation, which can include an increased risk of diabetes, a weakened immune system, and high blood pressure.

Napping can be beneficial, but only if done correctly

Napping can be beneficial for adults, and there is no need to feel lazy for indulging in daytime sleep. A short nap in the mid-afternoon can boost memory, improve job performance, lift your mood, make you more alert, and ease stress. However, napping for too long can affect sleep quality overnight and may lead to health problems. It is important to keep naps short, with 10 to 30 minutes being ideal, as anything longer can result in sleep inertia, which is a period of grogginess and confusion after waking up.

The best time for a nap is in the afternoon, between 1 pm and 3 pm, when humans naturally experience a dip in alertness. Napping at this time can help improve nighttime sleep, especially when combined with moderate exercise in the evening. Napping can be especially beneficial for older individuals, as it increases their total sleep time and provides measurable cognitive benefits without causing daytime drowsiness.

Napping can be a great way to boost your energy and productivity, but it should be done in moderation and at the right time of day. By keeping naps short and timed correctly, you can maximize the benefits and avoid any negative consequences.

The drawbacks of napping

While napping can be beneficial, it is important to be aware of its potential drawbacks. Firstly, napping for too long can negatively impact your sleep quality at night, leading to a disrupted sleep schedule and sleep disorders such as insomnia. This is especially true if you become dependent on naps instead of consistent nighttime sleep. Additionally, there is an increased risk of certain health problems associated with napping. For older adults, daytime napping is linked to self-reported sleep problems, such as frequent waking during the night.

Furthermore, a study in China found a correlation between napping for more than 90 minutes and high blood pressure in middle-aged and older women. Another study focusing on older Chinese individuals discovered that naps exceeding 30 minutes were associated with a higher prevalence of non-alcoholic fatty liver disease. An analysis of multiple studies also suggested that daily napping for over 60 minutes could increase the risk of developing type 2 diabetes. Moreover, a large-scale study in France found that napping was more prevalent among individuals with anxiety, depression, obesity, high blood pressure, and type 1 and type 2 diabetes.

It is worth noting that the relationship between napping and nighttime sleep is not yet fully understood, and more research is needed to determine how the frequency and duration of naps influence overall well-being. However, it is recommended that adults take naps at least eight hours before bedtime, typically before 3 pm, to minimise the potential disruption to their nighttime sleep.

Catching up on lost sleep

Sleep is a restorative activity that helps the brain to catalogue information and heal the body. While you sleep, your brain creates new pathways that help you navigate the day ahead. Sleeping also heals and repairs your blood vessels and heart.

Although you can make up for lost sleep, it's not quite the same as getting the sleep you need in the first place. When you do catch up, it takes extra time for your body to recover. According to a 2016 study, it takes four days to fully recover from one hour of lost sleep.

• Go to sleep 15 minutes earlier each night until you reach your desired bedtime.
• Avoid sleeping later than two hours past your normal wake-up time, even on weekends.
• Keep electronics in a separate room.
• Review your evening routine to see if anything is keeping you up too late.
• Stop using electronics two hours before bedtime.
• Make sure your bedroom is dark, quiet, and cool.
• Avoid caffeine late at night.
• Exercise no later than three hours before bedtime.
• Avoid naps, except for 20-minute power naps.

If you experience chronic sleep debt, the above recommendations may not be enough. Instead, you may need to make some long-term changes.

• Stick to a regular sleep schedule.
• Establish a bedtime routine with relaxing activities such as reading, taking a bath, or doing yoga.
• Avoid activities that might inhibit sleep, such as screen time, vigorous exercise, heavy meals, and consuming alcohol or caffeine, a few hours before bedtime.
• Create a soothing sleep environment by keeping the bedroom dark, quiet, and cool, and using comfortable bedding.
• Take steps for better sleep during the day, such as getting exposure to sunshine and physical activity early in the day.

Sleep debt and its effects

Sleep debt, also known as sleep deficit, is the difference between the amount of quality sleep you got and the amount of quality sleep you needed. It can make you feel even more tired than normal, and you may need to sleep more to feel rested.

Health Risks of Sleep Debt

• Increased risk of colorectal cancer: Sleep debt can lead to a 36% increased risk of developing colorectal cancer.
• Weaker immune system: Sleep debt can cause a decrease in natural killer cells, which are important for fighting off illnesses.
• Increased risk of type 2 diabetes: Research has shown that people with sleep debt are nearly three times more likely to develop type 2 diabetes.
• Higher risk of heart disease: Sleep debt is associated with a 48% increased risk of developing heart disease.
• High blood pressure: Sleep debt can lead to an increased risk of high blood pressure.
• Increased susceptibility to illness: Sleep debt can make you three times more likely to catch a cold.
• Drowsy driving: Sleep debt can increase the risk of car crashes, with 6,000 fatal crashes in the US each year caused by drowsy driving.
• Poor judgement: Sleep debt can impair judgement, leading to risky behaviours such as driving while tired.
• Unhealthy eating: Sleep debt can lead to increased cravings for sweet, salty and savoury foods.
• Weight gain: Sleep debt can cause higher levels of the hunger hormone ghrelin and lower levels of the appetite-control hormone leptin, leading to a 50% higher risk of obesity.
• Dementia: Sleep debt can increase the risk of dementia by 33%.
• Brain ageing: Sleep debt can age your brain by 3-5 years.

Tips for improving sleep quality

While it is possible to make up for lost sleep, it is not advisable to rely on this as a regular practice. Catching up on sleep takes extra time for your body to recover, and chronically losing sleep can lead to health issues. Here are some tips to improve your sleep quality:

• Stick to a sleep schedule: Go to bed and wake up at the same time every day, even on weekends. Consistency can significantly impact your sleep quality.
• Make time for sleep: Choose a bedtime that allows you to get the recommended amount of sleep for your age, usually seven to nine hours for adults.
• Establish a bedtime routine: Engage in relaxing activities before bed, such as reading, listening to soothing music, or practising relaxation techniques like mindfulness or meditation.
• Avoid bright lights and electronics before bed: The light from electronic devices can disrupt your body's natural sleep-wake functions and suppress melatonin production. Try to disconnect an hour or two before bedtime.
• Maintain a cool, dark, and quiet bedroom environment: Keep your bedroom cool, between 65 to 68 degrees Fahrenheit, and minimise noise and light. Consider using blackout curtains, earplugs, or a white noise machine.
• Get natural light exposure during the day: Sunlight exposure helps regulate your body's internal clock. If natural light is not accessible, you can use a light therapy box.
• Exercise regularly, but not too close to bedtime: Daily exercise improves sleep quality, but intense exercise close to bedtime may hinder your ability to settle down for sleep. Aim for at least 20 minutes of exercise daily, finishing at least three hours before bed.
• Limit caffeine and alcohol intake: Avoid caffeine at least eight hours before bedtime, and refrain from alcohol in the hours leading up to bedtime, as it can negatively impact sleep quality.
• Optimise your bedroom environment: Ensure your bed is comfortable and inviting, with a supportive mattress and pillow. Keep your bedroom well-ventilated and minimise allergens and carbon dioxide levels.
• Avoid late dinners and limit evening snacks: Eating late at night can disrupt sleep quality. Finish dinner a few hours before bed, and opt for a light snack if needed.
• Limit fluid intake before bed: Reduce your fluid intake in the evening to minimise the likelihood of nocturnal urination, which can interrupt your sleep.
• Consider supplements: Discuss the use of supplements like melatonin, valerian, chamomile, or glycine with your healthcare provider.

Frequently asked questions