Sleep duration significantly affects life expectancy. Adequate sleep is essential for the proper functioning of physiological systems as the living human body is sustained by a daily cycle of repair and growth that take place during sleep. As such, Without proper sleep, restorative cycles are not fully completed and the risk of dying prematurely increases.

The 7 Hour Sweet Spot

Importantly, the sweet spot for most adult is 7 hours of sleep per night. Specifically, individuals who sleep 6 hours or less or 9 hours or more per day have a higher risk of mortality.¹ The figure below illustrates the U-Shaped relationship between sleep duration and mortality. There is actually a dose-response relationship between sleep duration and all-cause mortality. Meaning that every hour of sleep, or lack off, outside the 7 hours optimal point, increases the risk of mortality.  Interestingly, the curve is steeper on the right side. Indicating that heavy sleeper have higher risk of all-cause mortality than sleep-deprived individuals.

How Insufficient Sleep Affects Life Expectancy

Compared to individuals who sleep on average 7 hours per day, individuals who sleep less than 5 hours per day are 70 % more likely to die from influenza and pneumonia² , 66% more likely to die from cardiovascular diseases ³, 33 % more likely to die from motor vehicle accident ⁴, 26 % more likely to die from a fall ⁵ and 9 % more likely to die from diabetes ⁶. Below are the reasons why insufficient sleep leads to these conditions.

Influenza and pneumonia

The reason why individuals with inadequate sleep habits die more frequently from infections like influenza and pneumonia is that sleep regulates the immune system and help control inflammation. Specifically, during sleep, the body produces cytokines, which are proteins that help to fight off infections and inflammation. These cytokines are essential for the proper functioning of the immune system and they help to coordinate the body’s response to pathogens and foreign invaders. As such, chronic sleep deprivation or poor sleep quality leads to an increased risk of infections.

In addition to cytokine production, sleep also helps to regulate the balance between the sympathetic and parasympathetic nervous systems, which play a key role in immune function. During sleep, the body is able to shift into a parasympathetic state, which is associated with a reduced stress response and an increased ability to fight off infections.

Cardiovascular diseases

Sleep invokes the activation of the parasympathetic nervous system, which is responsible for promoting relaxation and restorative processes in the body. It is often referred to as the “rest and digest” system, as it helps to conserve energy and promote digestion. Activation of the parasympathetic system causes the heart rate to slow down, blood vessels to dilate and digestion to increase. It also promotes the release of hormones that promote relaxation and well-being, such as serotonin and oxytocin.

Fall and Motor vehicle accidents

Sleep deprivation impairs cognitive function and increase the risk of accidents, including motor vehicle accidents, falls and occupational accidents. That is because Sleep allows the brain to carry out neural restorative processes that underlies one’s awareness and critical judgement. Namely, during sleep, the body redirects energy and resources towards restorative processes that are critical for cellular repair and regeneration. All cells in the body are affected by a deficient regenerative process caused by inadequate sleep and ill-functioning neural cells have a significantly increase the risk of accidents because of the lapses in attention and errors in judgement it causes. 

How Excessive Sleep Affects Life Expectancy

Excessive sleep, particularly consistently sleeping longer than 9 hours per day is associated with an increased risk of premature death. While insufficient sleep can be the cause of certain conditions, excessive sleep can act as both the effect and the cause of certain conditions that eventually leads to death. That is, excessive sleep duration can be a symptom of underlying health conditions. Namely, chronic conditions such as cardiovascular diseases, immunological conditions, sleep apnea, diabetes, obesity and depression often cause individuals to sleep longer. Furthermore, excessive sleep exacerbates chronic conditions through the disruption of the circadian rhythms (aka, the body clock) which leads to dysregulation of the cardiovascular and immune systems. The imbalance that results further increase the risk of death in individuals that are already affected by chronic conditions. That is a reason why the risk of death rises more steeply on the right side of the U-shaped graph above.  

Specifically, compared to individuals who sleep on average 7 hours per day, individuals who sleep more than 9 hours per day are 81% more likely to die from cardiovascular diseases³, 49 % more likely to die from influenza and pneumonia², 7 % more likely to die from diabetes⁶ and 5 % more likely to die from a fall ⁵.

Closing Remarks

Predicting life expectancy is complex and needs to take many factors into consideration. Youlldie allows to visualize how sleep interacts with other factors like gender, race, world region, income, education, alcohol, tobacco, physical activity, blood pressure, body mass index and family history to statistically predict life expectancy.

1. Jin Q, Yang N, Dai J, Zhao Y, Zhang X, Yin J, Yan Y. Association of Sleep Duration With All-Cause and Cardiovascular Mortality: A Prospective Cohort Study. Front Public Health. 2022 Jul 15;10:880276. doi: 10.3389/fpubh.2022.880276. PMID: 35910926; PMCID: PMC9334887. https://pubmed.ncbi.nlm.nih.gov/35910926/.
2. Patel SR, Malhotra A, Gao X, Hu FB, Neuman MI, Fawzi WW. A prospective study of sleep duration and pneumonia risk in women. Sleep. 2012 Jan 1;35(1):97-101. doi: 10.5665/sleep.1594. PMID: 22215923; PMCID: PMC3242694. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3242694/
3. Jin Qiman, Yang Niannian, Dai Juan, Zhao Yuanyuan, Zhang Xiaoxia, Yin Jiawei, Yan Yaqiong. Association of Sleep Duration With All-Cause and Cardiovascular Mortality: A Prospective Cohort Study, Frontiers in Public Health, vol 10, 2022, DOI=10.3389/fpubh.2022.880276. https://www.frontiersin.org/articles/10.3389/fpubh.2022.880276
4. Gottlieb DJ, Ellenbogen JM, Bianchi MT, Czeisler CA. Sleep deficiency and motor vehicle crash risk in the general population: a prospective cohort study. BMC Med. 2018 Mar 20;16(1):44. doi: 10.1186/s12916-018-1025-7. PMID: 29554902; PMCID: PMC5859531. https://pubmed.ncbi.nlm.nih.gov/29554902/
5. Noh JW, Kim KB, Lee JH, Lee Y, Lee BH, Kwon YD. Association between Sleep Duration and Injury from Falling among Older Adults: A Cross-Sectional Analysis of Korean Community Health Survey Data. Yonsei Med J. 2017 Nov;58(6):1222-1228. doi: 10.3349/ymj.2017.58.6.1222. PMID: 29047248; PMCID: PMC5653489. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5653489/
6. Shan Z, Ma H, Xie M, Yan P, Guo Y, Bao W, Rong Y, Jackson CL, Hu FB, Liu L. Sleep duration and risk of type 2 diabetes: a meta-analysis of prospective studies. Diabetes Care. 2015 Mar;38(3):529-37. doi: 10.2337/dc14-2073. PMID: 25715415. https://diabetesjournals.org/care/article/38/3/529/37556/Sleep-Duration-and-Risk-of-Type-2-Diabetes-A-Meta