Whether you’re a morning person or a night owl, the science says you should have 7-8 hours of shut-eye per night for optimal health. It’s not just that you’ll think and feel better, but you’ll be protecting yourself from viruses and bacteria.

Natural killer (NK) cells are critical to the innate immune system and certain protective proteins called cytokines need to increase if you have an infection, inflammation or if you’re stressed. Sleep deprivation – and we’re talking just one night! – can significantly reduce the number of those NK cells and protective cytokines.

If you’ve been burning the midnight oil and are vulnerable, then that’s when Leapfrog IMMUNE can spring into action as a back-up to balance your immune system and defend you against germs (sleep and Leapfrog are perfect bedfellows if you’re under the weather).

Kasia Kowalska, a psychologist and psychotherapist in Gdansk, Poland, is a huge advocate for sleep and explains how and why getting enough sleep is fundamental to a healthy life.

Does it matter how long we sleep?

Sleep duration of 7-8 hours is most favourable for a healthy and long life. While there is no one-size-fits-all prescription on how many hours of sleep every person needs, the evidence is clear that for most of us it is 7-8 hours. The scientific studies that have included over 4 million participants from 30 countries show that this sleep duration is optimal for health [1]. For example, compared with 7 hours of sleep, sleeping 6 hours is associated with 6% increase in mortality, 11% higher risk of cardiovascular heart disease and 9% higher risk of type 2 diabetes, and sleeping less than 6 hours is linked to 38% increase in obesity. Another study [2] established that sleeping 5 hours or less (on both weekdays and weekends), is associated with a 65% increase in mortality compared to sleeping 6-7 hours! My advice: be in bed on time.

What impact does lack of sleep have on the immune system?

Not getting enough sleep compromises immunity. In times of Covid there is a lot of focus on ‘immunity-boosting’. So, until a vaccination or a cure exists, our best chance is to act responsibly and rely on natural defences, and immunity is strongly linked to sleep. In one study [3], the participants were infected with rhinovirus and monitored for symptoms of a common cold. Those sleeping less than 7 hours were 2.94 times more likely to develop a cold than those sleeping more. It is chronic sleep deprivation that is detrimental to the immune system [4]. This makes evolutionary sense: an acute sleep loss occurring while in danger may mobilize the system, but exposed to longer sleep loss, the same system eventually starts failing. This is worth considering when many of us are constantly cutting down sleep.

Do we need to rely on sleep so much if we get the flu vaccine to protect us?

Sleep helps vaccines work. Vaccination remains the most effective way to prevent influenza, yet research demonstrates that it can be ineffective in as many as 33-49% cases [5]. This may have various reasons, but sleep plays a role. In a sample of healthy young and middle-aged adults, shorter sleep durations were related to the reduced influenza vaccine response [6]. In a study in which the researchers restricted sleep times of young men to 4 hours for 4 nights before administering the vaccine, ten days after vaccination, mean antibody levels were less than half for those immunised in a state of sleep debt, compared to those sleeping normally [7]. Please have this in mind before you go for your next shot.

What if we’re just too busy to sleep?

7-8 hours of sleep are best for optimal brain performance. Cognitive abilities are about how easily and efficiently we learn, react to change, focus our attention, or find solutions. No doubt, this is key for success at work, school and in personal life. We need those skills, and we certainly don’t want them to be impaired, yet they are if we neglect sleep. According to research on a global sample of over 10,000 people, statistically we achieve the best cognitive performance sleeping 7-8 hours per night [8]. With less sleep, our skills worsen. The effect is most significant for complex skills such as manipulating information to solve problems, and less visible for basic skills such as short-term memory. So, don’t be tempted to think that cutting down sleep can help you achieve more – it is the opposite.

Besides the quantity of hours, how can we get better quality sleep??

Use light & darkness to improve your sleep. Our sleep-wake cycles depend on light & darkness (circadian rhythm), yet we don’t live in a world anymore in which light & darkness provide the natural rhythm for our activity and rest. We are deprived of daylight – spending the days in buildings – and we are deprived of darkness – using technological advances at night. This disrupts sleep severely and some of the easiest ways to restore it are to increase daylight exposure in the morning [9], limit artificial light in the evening [10] and reduce any light pollution at night [11]. This can be as easy as taking a walk to work or sitting closer to a window, dimming lights and shutting off the TV while preparing for sleep, and making your bedroom completely dark.

And the best time to sleep? Between 10pm and 6am when our bodies’ natural circadian rhythm mimics the sunset and sunrise.

Follow Kasia @thescienceofsleeping on Instagram

References

[1] Chaput, J.-P., Dutil, C., Featherstone, R., Ross, R., Giangregorio, L., Saunders, T.J., et al. (2020). Sleep duration and health in adults: an overview of systematic reviews. Appl. Physiol. Nutr. Metab. 45(10 Suppl. 2).
[2] Åkerstedt, T., Ghilotti, F., Grotta, A., Zhao, H., Adami, H.-O., Trolle-Lagerros, Y., & Bellocco, R. (2018). Sleep duration and mortality – Does weekend sleep matter? Journal of Sleep Research, e12712.
[3] Cohen, S., Doyle, W. J., Alper, C. M., Janicki-Deverts, D., & Turner, R. B. (2009). Sleep Habits and Susceptibility to the Common Cold. Archives of Internal Medicine, 169(1), 62.
[4] Bryant, P. A., Trinder, J., & Curtis, N. (2004). Sick and tired: does sleep have a vital role in the immune system? Nature Reviews Immunology, 4(6), 457–467.
[5] Osterholm, M. T., Kelley, N. S., Sommer, A., & Belongia, E. A. (2012). Efficacy and effectiveness of influenza vaccines: A systematic review and meta-analysis. Lancet Infectious Diseases, 12(1), 36–44.
[6] Miller, G. E., Cohen, S., Pressman, S., Barkin, A., Rabin, B. S., & Treanor, J. J. (2004). Psychological stress and antibody response to influenza vaccination: When is the critical period for stress, and how does it get inside the body? Psychosomatic Medicine, 66(2), 215–223.
[7] Spiegel, K., Sheridan, J. F., & Van Cauter, E. (2002). Effect of sleep deprivation on response to immunizaton. Journal of the American Medical Association, 288(12), 1471–1472.
[8] Wild , C. J., Nichols, E. S., Battista, M. E., Stojanoski, B., & Owen, A. M. (2018). Dissociable effects of self-reported daily sleep duration on high-level cognitive abilities.
[9] Figueiro, M. G., Steverson, B., Heerwagen, J., Kampschroer, K., Hunter, C. M., …, Rea, M. S. (2017). The impact of daytime light exposures on sleep and mood in office workers. Sleep Health, 3(3), 204–215.
[10] Gooley, J. J., Chamberlain, K., Smith, K. A., Khalsa, S. B. S., Rajaratnam, S. M. W., … Lockley, S. W. (2011). Exposure to Room Light before Bedtime Suppresses Melatonin Onset and Shortens Melatonin Duration in Humans. The Journal of Clinical Endocrinology & Metabolism, 96(3), E463–E472.
[11] Falchi, F., Cinzano, P., Elvidge, C. D., Keith, D. M., & Haim, A. (2011). Limiting the impact of light pollution on human health, environment and stellar visibility. Journal of Env. Management, 92(10), 2714–2722.