Sleeping Well

Our assessments of evidence for each medical benefit fall into one of these categories:

• Strong evidence: consistent, significant effects in several large (or at least one very large) well designed clinical studies or at least two meta-analysesa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of clinical studies of moderate or better quality (or one large meta-analysis) finding similar results
• Good evidence: significant effects in one large or several mid-sized and well-designed clinical studies ( randomized controlled trialsa study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects with an appropriate placebo or other strong comparison control or observational studies that control for confounds)
• Modest evidence: significant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies), or several small studies aggregated into a meta-analysis
• Preliminary evidence: significant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect
• Weak evidence: one or more case studies, supported by animal evidence OR small treatment effects of limited clinical significance OR studies with no controls OR weak trends of effects
• Insufficient evidence: preclinical evidence only OR clinical studies with such poor or unclear methodology that no conclusion can be drawn OR conflicting findings across clinical studies with no preponderance of evidence in one direction; conflicting evidence occurs when studies find conflicting effects (positive effect vs no effect or negative effect) with the same treatment and the same general study population (same cancer type, for example)

• 9% higher cancer mortality, especially lung cancer, among people with cancer with 9 to 10 hours of sleep per day compared to 7 or 8 hours in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 32 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹Stone CR, Haig TR et al. The association between sleep duration and cancer-specific mortality: a systematic review and meta-analysis. Cancer Causes and Control. 2019 May;30(5):501-525.
• 3% higher cancer mortality, especially lung cancer, among people with cancer with 5 to 6 hours of sleep per day compared to 7 or 8 hours in a meta-analysis of 32 observational studies²Stone CR, Haig TR et al. The association between sleep duration and cancer-specific mortality: a systematic review and meta-analysis. Cancer Causes and Control. 2019 May;30(5):501-525.

• Substantially better survival (5 times as high at 2 years) among people with metastatic colorectal cancer who had substantially different day and night activity levels compared to those with more similar activity levels day and night in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study³Mormont MC, Waterhouse J et al. Marked 24-h rest/activity rhythms are associated with better quality of life, better response, and longer survival in patients with metastatic colorectal cancer and good performance status. Clinical Cancer Research. 2000 Aug;6(8):3038-45.
• Better overall survival among people with metastatic colorectal cancer receiving chemotherapy with substantially different day and night activity levels compared to those with more similar activity levels day and night in a small observational study⁴Innominato PF, Giacchetti S et al. Prediction of overall survival through circadian rest-activity monitoring during chemotherapy for metastatic colorectal cancer. International Journal of Cancer. 2012 Dec 1;131(11):2684-92.
• Better first-line progression-free survival with better sleep quality, and better overall survival with shorter sleep latency among people with advanced lung cancer in a small observational study⁵He Y, Sun LY et al. Sleep quality, anxiety and depression in advanced lung cancer: patients and caregivers. BMJ Supportive and Palliative Care. 2020 Apr 6:bmjspcare-2018-001684.
• Better treatment outcomes including survival among people with metastatic colorectal cancer with normal rest/activity patterns compared to people with disrupted rest/activity circadianrecurring naturally on a twenty-four-hour cycle; your sleep-wake cycle reflects your alignment to the daily cycle, and a mismatch is called circadian disruption rhythms in a small observational study⁶Rich T, Innominato PF et al. Elevated serum cytokines correlated with altered behavior, serum cortisol rhythm, and dampened 24-hour rest-activity patterns in patients with metastatic colorectal cancer. Clinical Cancer Research. 2005 Mar 1;11(5):1757-64.
• Better survival among people with metastatic breast cancer who had bigger differences in cortisol levels between day and night compared to similar day and night levels in a mid-sized observational study⁷Sephton SE, Sapolsky RM, Kraemer HC, Spiegel D. Diurnal cortisol rhythm as a predictor of breast cancer survival. Journal of the National Cancer Institute. 2000 Jun 21;92(12):994-1000.
• Greater tumor regression among people with metastatic non-small cell lung cancer receiving chemotherapy with lower alteration of the cortisol rhythm in a small observational study⁸Lissoni P, Messina G et al. Efficacy of cancer chemotherapy in relation to synchronization of cortisol rhythm, immune status and psychospiritual profile in metastatic non-small cell lung cancer. In Vivo. 2008 Mar-Apr;22(2):257-62.

• “Short sleep duration has been consistently associated with increased risk of obesity” in a review of 11 meta-analysesa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study⁹Antza C, Kostopoulos G, Mostafa S, Nirantharakumar K, Tahrani A. The links between sleep duration, obesity and type 2 diabetes mellitus. Journal of Endocrinology. 2021 Dec 13;252(2):125-141.
• Moderately higher risk of obesity among both adults and children with inadequate sleep compared to other people in a very large meta-analysis of 30 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies¹⁰Cappuccio FP, Taggart FM et al. Meta-analysis of short sleep duration and obesity in children and adults. Sleep. 2008 May;31(5):619-26.
• A link between higher body mass index, higher body weight, or larger waist circumference and either short sleep duration or long sleep duration in a large observational study; sleep duration of 6 to 7 hours is associated with the lowest measures of obesity¹¹Brady EM, Bodicoat DH et al. Sleep duration, obesity and insulin resistance in a multi-ethnic UK population at high risk of diabetes. Diabetes Research and Clinical Practice. 2018 May;139:195-202.

Shorter self-reported sleep duration is linked to an increased incidence of type 2 diabetes. Decreasing either the amount or quality of sleep decreases insulin sensitivity and decreases glucose tolerance.¹²Nedeltcheva AV, Scheer FA. Metabolic effects of sleep disruption, links to obesity and diabetes. Current Opinion in Endocrinology, Diabetes, and Obesity. 2014 Aug;21(4):293-8.

• Twice the risk of being diagnosed with prediabetes and type 2 diabetes among short sleepers (5–6 hours per day), and almost 60% higher risk of developing type 2 diabetes among long sleepers (more than 8 hours per day) compared to normal sleepers (7–8 hours per day) in a review of 10 meta-analysesa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study¹³Antza C, Kostopoulos G, Mostafa S, Nirantharakumar K, Tahrani A. The links between sleep duration, obesity and type 2 diabetes mellitus. Journal of Endocrinology. 2021 Dec 13;252(2):125-141.
• High levels of insulin (hyperinsulinemia), blood sugar (hyperglycemia), and overall insulin resistance among healthy young men experiencing 4 nights of sleep restriction of 4 hours per night compared to controls in a small RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects¹⁴Liu PY, Lawrence-Sidebottom D et al. Clamping cortisol and testosterone mitigates the development of insulin resistance during sleep restriction in men. Journal of Clinical Endocrinol Metab. 2021 Aug 18;106(9):e3436-e3448.
• Higher fasting insulin levels among people with longer sleep durations compared to short durations in a large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study¹⁵Brady EM, Bodicoat DH et al. Sleep duration, obesity and insulin resistance in a multi-ethnic UK population at high risk of diabetes. Diabetes Research and Clinical Practice. 2018 May;139:195-202.
• A weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently) toward a better marker of blood sugar among people with sleep disturbances who reported better sleep quality in response to sleep interventions in a meta-analysis of a subset of 22 intervention studies¹⁶Kothari V, Cardona Z, Chirakalwasan N, Anothaisintawee T, Reutrakul S. Sleep interventions and glucose metabolism: systematic review and meta-analysis. Sleep Medicine. 2021 Feb;78:24-35.

• Higher leptin to adiponectin ratios among people with longer sleep durations compared to short durations in a large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study¹⁷Brady EM, Bodicoat DH et al. Sleep duration, obesity and insulin resistance in a multi-ethnic UK population at high risk of diabetes. Diabetes Research and Clinical Practice. 2018 May;139:195-202.

• Altered rhythm of granulocytes―important in fighting bacterial infections―among healthy young men with significant daily (diurnal) rhythms at baseline when experiencing 29 hours of extended wakefulness compared to baseline in a small uncontrolled triala study in which a therapy is used, but without a comparison group against which to judge outcomes; an uncontrolled trial is considered a weak study design¹⁸Ackermann K, Revell VL et al. Diurnal rhythms in blood cell populations and the effect of acute sleep deprivation in healthy young men. Sleep. 2012 Jul 1;35(7):933-40.

• Higher markers of inflammation among people with metastatic colorectal cancer with disrupted rest/activity circadianrecurring naturally on a twenty-four-hour cycle; your sleep-wake cycle reflects your alignment to the daily cycle, and a mismatch is called circadian disruption rhythms compared to people with better rhythms in a small observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study¹⁹Rich T, Innominato PF et al. Elevated serum cytokines correlated with altered behavior, serum cortisol rhythm, and dampened 24-hour rest-activity patterns in patients with metastatic colorectal cancer. Clinical Cancer Research. 2005 Mar 1;11(5):1757-64.
• Higher markers of inflammation among healthy volunteers with sleep deprivation or restriction compared to baseline or controls in small RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects and clinical trials²⁰Motivala SJ. Sleep and inflammation: psychoneuroimmunology in the context of cardiovascular disease. Annals of Behavioral Medicine. 2011 Oct;42(2):141-52.

• Alterations in fecal microbiome among women who had sleep disturbance before breast cancer surgery compared to those with less sleep disturbance in a small observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study²¹Yao ZW, Zhao BC et al. Relationships of sleep disturbance, intestinal microbiota, and postoperative pain in breast cancer patients: a prospective observational study. Sleep and Breathing. 2020 Nov 19.
• No evidence of an effect on the fecal microbiome among healthy volunteers with short-term lack of sleep (sleep restriction) compared to baseline in a small uncontrolled triala study in which a therapy is used, but without a comparison group against which to judge outcomes; an uncontrolled trial is considered a weak study design²²Zhang SL, Bai L et al. Human and rat gut microbiome composition is maintained following sleep restriction. Proceedings of the National Academy of Sciences of the United States of America. 2017 Feb 21;114(8):E1564-E1571.

The relationship between pain and anxiety is bidirectional—each can trigger and impact the other.²³Thielking PD. Cancer pain and anxiety. Current Pain and Headache Reports. 2003 Aug;7(4):249-61; Theobald DE. Cancer pain, fatigue, distress, and insomnia in cancer patients. Clinical Cornerstone. 2004;6 Suppl 1D:S15-21.

• Lower levels of anxiety among people with breast cancer reporting feeling refreshed after sleep, and higher levels among people reporting sleep disturbance in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study²⁴Cho OH, Hwang KH. Association between sleep quality, anxiety and depression among Korean breast cancer survivors. Nursing Open. 2021 May;8(3):1030-1037.
• Higher levels of anxiety among people with lung cancer who reported poor sleep quality compared to other people in a mid-sized observational study²⁵Papadopoulos D, Kiagia M, Charpidou A, Gkiozos I, Syrigos K. Psychological correlates of sleep quality in lung cancer patients under chemotherapy: a single-center cross-sectional study. Psycho-Oncology. 2019 Sep;28(9):1879-1886.
• Worse anxiety among people with colorectal cancer with higher preoperative insomnia compared to no insomnia in a mid-sized observational study²⁶Sun GW, Yang YL et al. Preoperative insomnia and its association with psychological factors, pain and anxiety in Chinese colorectal cancer patients. Supportive Care in Cancer. 2020 Jun;28(6):2911-2919.

• Substantially fewer people experiencing unintentional weight loss of 5% or more of body weight among people with metastatic colorectal cancer receiving chemotherapy who had substantially different day and night activity levels compared to those with more similar activity levels day and night in a small observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study²⁷Innominato PF, Giacchetti S et al. Prediction of overall survival through circadian rest-activity monitoring during chemotherapy for metastatic colorectal cancer. International Journal of Cancer. 2012 Dec 1;131(11):2684-92.

• Less appetite loss among people with metastatic colorectal cancer with normal rest/activity patterns compared to people with disrupted rest/activity circadianrecurring naturally on a twenty-four-hour cycle; your sleep-wake cycle reflects your alignment to the daily cycle, and a mismatch is called circadian disruption rhythms in a small observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study²⁸Rich T, Innominato PF et al. Elevated serum cytokines correlated with altered behavior, serum cortisol rhythm, and dampened 24-hour rest-activity patterns in patients with metastatic colorectal cancer. Clinical Cancer Research. 2005 Mar 1;11(5):1757-64.

• Lower levels of depression among people with breast cancer reporting feeling refreshed after sleep, and higher levels among people reporting poor sleep quality or longer sleep latency, and a weak trend toward less depression with longer sleep duration in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study²⁹Cho OH, Hwang KH. Association between sleep quality, anxiety and depression among Korean breast cancer survivors. Nursing Open. 2021 May;8(3):1030-1037.
• Higher levels of depressive symptoms among men recently treated for prostate cancer who reported poor sleep quality compared to those with better sleep quality in a small observational study³⁰Hoyt MA, Bower JE, Irwin MR, Weierich MR, Stanton AL. Sleep quality and depressive symptoms after prostate cancer: the mechanistic role of cortisol. Behavioral Neuroscience. 2016;130(3):351-356.

• Less fatigue among people with metastatic colorectal cancer receiving chemotherapy who had substantially different day and night activity levels compared to those with more similar activity levels day and night in mid-sized³¹Mormont MC, Waterhouse J et al. Marked 24-h rest/activity rhythms are associated with better quality of life, better response, and longer survival in patients with metastatic colorectal cancer and good performance status. Clinical Cancer Research. 2000 Aug;6(8):3038-45. and small³²Innominato PF, Giacchetti S et al. Prediction of overall survival through circadian rest-activity monitoring during chemotherapy for metastatic colorectal cancer. International Journal of Cancer. 2012 Dec 1;131(11):2684-92. observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies
• Higher levels of fatigue among people with lung cancer who reported poor sleep quality compared to other people in a mid-sized observational study³³Papadopoulos D, Kiagia M, Charpidou A, Gkiozos I, Syrigos K. Psychological correlates of sleep quality in lung cancer patients under chemotherapy: a single-center cross-sectional study. Psycho-Oncology. 2019 Sep;28(9):1879-1886.
• More reported fatigue among people with lymphoma who also reported worse sleep quality compared to other people in a mid-sized observational study³⁴Starreveld DEJ, Habers GEA et al. Cancer-related fatigue in relation to chronotype and sleep quality in (non-)Hodgkin lymphoma survivors. Journal of Biological Rhythms. 2021 Feb;36(1):71-83.
• Less fatigue among people with metastatic colorectal cancer with normal rest/activity patterns compared to people with disrupted rest/activity circadianrecurring naturally on a twenty-four-hour cycle; your sleep-wake cycle reflects your alignment to the daily cycle, and a mismatch is called circadian disruption rhythms in a small observational study³⁵Rich T, Innominato PF et al. Elevated serum cytokines correlated with altered behavior, serum cortisol rhythm, and dampened 24-hour rest-activity patterns in patients with metastatic colorectal cancer. Clinical Cancer Research. 2005 Mar 1;11(5):1757-64.

The relationship between pain and sleep disturbance is bidirectional—each can trigger and impact the other.³⁶Theobald DE. Cancer pain, fatigue, distress, and insomnia in cancer patients. Clinical Cornerstone. 2004;6 Suppl 1D:S15-21.

• More reported pain within 6 months of completing cancer treatment among people with ovarian cancer regularly going to bed after midnight compared to earlier times in an observation from a mid-sized RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects³⁷Crane TE, Miller A, Skiba MB, Donzella S, Thomson CA. Association of chronotype and pain at baseline in ovarian cancer survivors participating in a lifestyle intervention (NRG/GOG 0225). Journal of Clinical Oncology. 2020;38(suppl) abstr 6018).
• More severe acute pain after surgery among women who had sleep disturbance before breast cancer surgery compared to those with less sleep disturbance in a small observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study³⁸Yao ZW, Zhao BC et al. Relationships of sleep disturbance, intestinal microbiota, and postoperative pain in breast cancer patients: a prospective observational study. Sleep and Breathing. 2020 Nov 19.
• Worse pain among people with colorectal cancer with higher preoperative insomnia compared to no insomnia in a mid-sized observational study³⁹Sun GW, Yang YL et al. Preoperative insomnia and its association with psychological factors, pain and anxiety in Chinese colorectal cancer patients. Supportive Care in Cancer. 2020 Jun;28(6):2911-2919.
• More opioid use in the first year after mastectomy among people with breast cancer with sleep disturbance compared to no sleep disturbance in a mid-sized observational study⁴⁰Azizoddin DR, Soens MA et al. Perioperative sleep disturbance following mastectomy: a longitudinal investigation of the relationship to pain, opioid use, treatment, and psychosocial symptoms. Journal of Clinical Oncology. 2021 Oct 1;39(28_suppl:192.

• Better quality of life among people with metastatic colorectal cancer who had substantially different day and night activity levels compared to those with more similar activity levels day and night in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study⁴¹Mormont MC, Waterhouse J et al. Marked 24-h rest/activity rhythms are associated with better quality of life, better response, and longer survival in patients with metastatic colorectal cancer and good performance status. Clinical Cancer Research. 2000 Aug;6(8):3038-45.
• Better performance status and emotional and social function among people with metastatic colorectal cancer with normal rest/activity patterns compared to people with disrupted rest/activity circadianrecurring naturally on a twenty-four-hour cycle; your sleep-wake cycle reflects your alignment to the daily cycle, and a mismatch is called circadian disruption rhythms in a small observational study⁴²Rich T, Innominato PF et al. Elevated serum cytokines correlated with altered behavior, serum cortisol rhythm, and dampened 24-hour rest-activity patterns in patients with metastatic colorectal cancer. Clinical Cancer Research. 2005 Mar 1;11(5):1757-64.
• Better quality of life during chemotherapy among people with better sleep scores compared to worse sleep scores in a small observational study⁴³Block KI, Block PB et al. Making circadian cancer therapy practical. Integrative Cancer Therapies. 2009 Dec;8(4):371-86.

• Higher levels of stress among people with lung cancer who reported poor sleep quality compared to other people in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study⁴⁴Papadopoulos D, Kiagia M, Charpidou A, Gkiozos I, Syrigos K. Psychological correlates of sleep quality in lung cancer patients under chemotherapy: a single-center cross-sectional study. Psycho-Oncology. 2019 Sep;28(9):1879-1886.

• A weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently) toward lower diet quality within 6 months of completing cancer treatment among people with ovarian cancer regularly going to bed after midnight compared to earlier times in an observation from a mid-sized RCT⁴⁵Crane TE, Miller A, Skiba MB, Donzella S, Thomson CA. Association of chronotype and pain at baseline in ovarian cancer survivors participating in a lifestyle intervention (NRG/GOG 0225). Journal of Clinical Oncology. 2020;38(suppl) abstr 6018).

• Higher risk of GERD among people with objective sleep disturbance or sleep apnea compared to other people in a review⁴⁶Jung HK, Choung RS, Talley NJ. Gastroesophageal reflux disease and sleep disorders: evidence for a causal link and therapeutic implications. Journal of Neurogastroenterology and Motility. 2010 Jan;16(1):22-9.

Short sleep durations (less than 6 hours): preliminary (conflicting) evidence of slightly higher risk of cancer mortality among people with short sleep durations

• 8% higher cancer mortality among people without cancer at baseline with 4 to 5 hours total sleep time compared to 8-hour sleep times in a very large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 14 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies⁴⁷Li Y, Cai S et al. Association between total sleep time and all cancer mortality: non-linear dose-response meta-analysis of cohort studies. Sleep Medicine. 2019 Aug;60:211-218.
• 5% higher cancer mortality among people without cancer at baseline with less than 6 hours sleep compared to more sleep in a meta-analysis of 11 observational studies⁴⁸Ma QQ, Yao Q, Lin L, Chen GC, Yu JB. Sleep duration and total cancer mortality: a meta-analysis of prospective studies. Sleep Medicine. 2016 Nov-Dec;27-28:39-44.
• No evidence of an effect on cancer-related mortality among people without cancer at baseline with short sleep duration in a meta-analysis of 23 studies⁴⁹Gallicchio L, Kalesan B. Sleep duration and mortality: a systematic review and meta-analysis. Journal of Sleep Research. 2009 Jun;18(2):148-58.

Long sleep durations (9 hours or more): good evidence of slightly to moderately higher cancer mortality among people without cancer at baseline with long sleep durations

• 5% increased cancer mortality among people without cancer at baseline with more than 8 hours, and especially 9 or more hours, of sleep time compared to 8 hours of sleep in a very large meta-analysis of 14 observational studies⁵⁰Li Y, Cai S et al. Association between total sleep time and all cancer mortality: non-linear dose-response meta-analysis of cohort studies. Sleep Medicine. 2019 Aug;60:211-218.
• 11% higher cancer mortality among people with 9–10 hours of sleep compared to less sleep in a meta-analysis of 11 observational studies⁵¹Ma QQ, Yao Q, Lin L, Chen GC, Yu JB. Sleep duration and total cancer mortality: a meta-analysis of prospective studies. Sleep Medicine. 2016 Nov-Dec;27-28:39-44.
• 21% higher cancer-related mortality among people without cancer at baseline with long sleep (more than 9 hours on a typical night) compared to average sleepers in a meta-analysis of 23 studies⁵²Gallicchio L, Kalesan B. Sleep duration and mortality: a systematic review and meta-analysis. Journal of Sleep Research. 2009 Jun;18(2):148-58.

Insomnia symptoms or napping: no evidence of higher cancer mortality among people with insomnia symptoms or who take daytime naps in combined analyses of studies

• No link between cancer-related mortality and insomnia symptoms among people without cancer at baseline compared to other people in a very large meta-analysis of 29 observational studies⁵³Ge L, Guyatt G et al. Insomnia and risk of mortality from all-cause, cardiovascular disease, and cancer: systematic review and meta-analysis of prospective cohort studies. Sleep Medicine Reviews. 2019 Dec;48:101215.
• No evidence of an effect on cancer-related mortality among people without cancer at baseline taking daytime naps compared to other people in a meta-analysis of 4 observational studies⁵⁴Zhong G, Wang Y, Tao T, Ying J, Zhao Y. Daytime napping and mortality from all causes, cardiovascular disease, and cancer: a meta-analysis of prospective cohort studies. Sleep Medicine. 2015 Jul;16(7):811-9.

Short sleep durations (less than 6 hours): no evidence of an effect on risk of breast cancer among people with short sleep duration in a combined analysis of studies

• No evidence of an effect on risk of breast cancer among people with short sleep duration compared to other people in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 28 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies⁵⁵He C, Anand ST, Ebell MH, Vena JE, Robb SW. Circadian disrupting exposures and breast cancer risk: a meta-analysis. International Archives of Occupational and Environmental Health. 2015 Jul;88: 533-47.

Long sleep durations (more than 9 hours): good evidence of lower risk of breast cancer among people with long sleep durations

• 21% lower risk of hormone-related cancers, including breast cancer, among people with longer sleep duration compared to other people in a very large meta-analysis of 12 observational studies⁵⁶Zhao H, Yin JY et al. Sleep duration and cancer risk: a systematic review and meta-analysis of prospective studies. Asian Pacific Journal of Cancer Prevention. 2013;14(12):7509-15.

• Almost 50% higher risk of colorectal adenomas among people sleeping less than 6 hours per night compared to those sleeping at least 7 hours per night in a large observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foodsstudy⁵⁷Thompson CL, Larkin EK et al. Short duration of sleep increases risk of colorectal adenoma. Cancer. 2011 Feb 15;117(4):841-7.
• 29% higher risk of colorectal cancer among people with sleep duration longer than 9 hours compared to less sleep in a very large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 12 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies⁵⁸Zhao H, Yin JY et al. Sleep duration and cancer risk: a systematic review and meta-analysis of prospective studies. Asian Pacific Journal of Cancer Prevention. 2013;14(12):7509-15.

• 76% higher risk of Barrett’s esophagus among people sleeping more than 6 hours a night compared to less than 6 in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 3 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies⁵⁹Zhao Z, Yin Z, Zhang C. Lifestyle interventions can reduce the risk of Barrett’s esophagus: a systematic review and meta-analysis of 62 studies involving 250,157 participants. Cancer Medicine. 2021;10(15):5297-5320.

• 21% lower risk of hormone-related cancers, including endometrial cancer, among people with sleep duration longer than 9 hours compared to less sleep in a very large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 12 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies⁶⁰Zhao H, Yin JY et al. Sleep duration and cancer risk: a systematic review and meta-analysis of prospective studies. Asian Pacific Journal of Cancer Prevention. 2013;14(12):7509-15.

• 21% lower risk of hormone-related cancers, including epithelial ovarian cancer, among people with sleep duration longer than 9 hours compared to less sleep in a very large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 12 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies⁶¹Zhao H, Yin JY et al. Sleep duration and cancer risk: a systematic review and meta-analysis of prospective studies. Asian Pacific Journal of Cancer Prevention. 2013;14(12):7509-15.
• No evidence of an effect of sleep quality on overall risk of ovarian cancer, but 27% lower risk of invasive serous subtype ovarian cancer among postmenopausal women with restful or very restful sleep quality compared to average sleep quality in a very large observational study⁶²Liang X, Harris HR et al. Sleep characteristics and risk of ovarian cancer among postmenopausal women. Cancer Prev Res (Phila). 2021 Jan;14(1):55-64.
• No evidence of an effect of insomnia on overall risk of ovarian cancer, but 36% higher risk of invasive serous subtype ovarian cancer among postmenopausal women with insomnia compared to no insomnia in a very large observational study⁶³Liang X, Harris HR et al. Sleep characteristics and risk of ovarian cancer among postmenopausal women. Cancer Prev Res (Phila). 2021 Jan;14(1):55-64.

• 21% lower risk of hormone-related cancers, including prostate cancer, among people with sleep duration longer than 9 hours compared to less sleep in a very large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 12 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies⁶⁴Zhao H, Yin JY et al. Sleep duration and cancer risk: a systematic review and meta-analysis of prospective studies. Asian Pacific Journal of Cancer Prevention. 2013;14(12):7509-15.

• 21% lower risk of hormone-related cancers, including thyroid cancer, among people with sleep duration longer than 9 hours compared to less sleep in a very large meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 12 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies⁶⁵Zhao H, Yin JY et al. Sleep duration and cancer risk: a systematic review and meta-analysis of prospective studies. Asian Pacific Journal of Cancer Prevention. 2013;14(12):7509-15.