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Showing 64 of 64 sources.
- Source [1]
NHLBI, 2022
Read the source (opens in a new tab)Insomnia: Causes and Risk Factors
National Heart, Lung, and Blood Institute (NIH) · 2022
Schedule and environment changes, stress, caffeine, alcohol, nicotine, screens near bedtime and clock-watching worry can cause or raise the risk of insomnia; menopause hormone changes can cause sleep problems.
- Source [2]
NHLBI, 2022
Read the source (opens in a new tab)Insomnia: Symptoms
National Heart, Lung, and Blood Institute (NIH) · 2022
Waking during the night is the most common insomnia symptom, more common in older adults; waking too early is also common.
- Source [3]
NHLBI, 2022
Read the source (opens in a new tab)Insomnia: Diagnosis
National Heart, Lung, and Blood Institute (NIH) · 2022
Talk to a doctor if poor sleep affects daily activities; keep a sleep diary for 1 to 2 weeks before the visit; a sleep study can look for problems such as sleep apnea.
- Source [4]
NINDS, 2025
Read the source (opens in a new tab)Brain Basics: Understanding Sleep
National Institute of Neurological Disorders and Stroke (NIH) · 2025
We cycle through non-REM and REM sleep several times a night; deep stage 3 sleep comes in longer periods in the first half of the night and REM periods lengthen later in the night.
- Source [5]
Ohayon et al., 2004
Read the source (opens in a new tab)Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals: developing normative sleep values across the human lifespan
Sleep · 2004
In healthy adults, time awake after first falling asleep increases with age while slow-wave sleep and sleep efficiency decrease.
- Source [6]
Bonnet & Arand, 2007
Read the source (opens in a new tab)EEG arousal norms by age
Journal of Clinical Sleep Medicine · 2007
Brief arousals occur in healthy sleepers, are an integral part of the sleep process, and become more frequent with age.
- Source [7]
Weitzman et al., 1971
Read the source (opens in a new tab)Twenty-four hour pattern of the episodic secretion of cortisol in normal subjects
Journal of Clinical Endocrinology and Metabolism · 1971
Classic study charting cortisol across 24 hours in healthy people, describing its release as episodic rather than steady. Historical background only.
- Source [8]
Chan & Debono, 2010
Read the source (opens in a new tab)Replication of cortisol circadian rhythm: new advances in hydrocortisone replacement therapy
Therapeutic Advances in Endocrinology and Metabolism · 2010
Citing a 24-hour study of 33 healthy people, cortisol is lowest around midnight, starts rising around 02:00 to 03:00, and peaks around 08:30.
- Source [9]
Fries et al., 2009
Read the source (opens in a new tab)The cortisol awakening response (CAR): facts and future directions
International Journal of Psychophysiology · 2009
Cortisol follows a daily cycle with a sharp rise after waking, influenced by sex, health status, health behavior and perceived stress.
- Source [10]
Stalder et al., 2016
Read the source (opens in a new tab)Assessment of the cortisol awakening response: Expert consensus guidelines
Psychoneuroendocrinology · 2016
The morning cortisol rise spans roughly the first 30 to 45 minutes after waking, and valid measurement depends on precisely timed saliva samples starting at waking.
- Source [11]
Adam et al., 2017
Read the source (opens in a new tab)Diurnal cortisol slopes and mental and physical health outcomes: A systematic review and meta-analysis
Psychoneuroendocrinology · 2017
Across 80 studies, a flatter morning-to-evening cortisol slope was associated with poorer mental and physical health (average r = 0.147).
- Source [12]
Leproult et al., 1997
Read the source (opens in a new tab)Sleep loss results in an elevation of cortisol levels the next evening
Sleep · 1997
In healthy young men, partial or total sleep loss was followed by 37% and 45% higher evening cortisol the next day, and a delayed evening quiet period.
- Source [13]
Drake et al., 2013
Read the source (opens in a new tab)Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed
Journal of Clinical Sleep Medicine · 2013
400 mg of caffeine disrupted sleep whether taken at bedtime, 3 hours or 6 hours before bed, compared with placebo.
- Source [14]
Lovallo et al., 2005
Read the source (opens in a new tab)Caffeine stimulation of cortisol secretion across the waking hours in relation to caffeine intake levels
Psychosomatic Medicine · 2005
Caffeine raised daytime cortisol; in regular users the response was reduced but not eliminated.
- Source [15]
Ebrahim et al., 2013
Read the source (opens in a new tab)Alcohol and sleep I: effects on normal sleep
Alcoholism: Clinical and Experimental Research · 2013
In healthy volunteers, alcohol at all doses sped sleep onset and consolidated the first half of the night but increased sleep disruption in the second half.
- Source [16]
Chang et al., 2015
Read the source (opens in a new tab)Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness
Proceedings of the National Academy of Sciences of the United States of America · 2015
Versus a printed book, reading a light-emitting e-reader before bed meant longer time to fall asleep, less melatonin, a later body clock and lower next-morning alertness.
- Source [17]
Blume et al., 2019
Read the source (opens in a new tab)Effects of light on human circadian rhythms, sleep and mood
Somnologie · 2019
The master body clock is kept aligned to the 24-hour day by light signals from the eyes, and light at night alters circadian rhythms and sleep.
- Source [18]
Maki et al., 2024
Read the source (opens in a new tab)Sleep disturbance associated with the menopause
Menopause · 2024
Menopause-related sleep disturbance is characterized by frequent night-time awakenings and more time awake after sleep onset, linked to hormone changes, hot flashes and mood symptoms.
- Source [19]
NHLBI, 2025
Read the source (opens in a new tab)Sleep Apnea: Symptoms
National Heart, Lung, and Blood Institute (NIH) · 2025
Sleep apnea symptoms include loud snoring, gasping, breathing that stops and starts, daytime sleepiness, insomnia and waking often at night to urinate.
- Source [20]
Carney et al., 2012
Read the source (opens in a new tab)The consensus sleep diary: standardizing prospective sleep self-monitoring
Sleep · 2012
Insomnia experts, with input from good sleepers and people with insomnia or sleep apnea, developed a standardized Consensus Sleep Diary.
- Source [21]
Schutte-Rodin et al., 2008
Read the source (opens in a new tab)Clinical guideline for the evaluation and management of chronic insomnia in adults
Journal of Clinical Sleep Medicine (AASM) · 2008
The AASM guideline recommends collecting sleep diary data before and during insomnia treatment.
- Source [22]
Cadegiani & Kater, 2016
Read the source (opens in a new tab)Adrenal fatigue does not exist: a systematic review
BMC Endocrine Disorders · 2016
A systematic review of 58 studies found no substantiation that adrenal fatigue is an actual medical condition.
- Source [23]
Endocrine Society, 2022
Read the source (opens in a new tab)Adrenal Fatigue
Endocrine Society · 2022
The Endocrine Society states no scientific proof supports adrenal fatigue as a true medical condition.
- Source [24]
NIDDK, 2018
Read the source (opens in a new tab)Cushing's Syndrome
National Institute of Diabetes and Digestive and Kidney Diseases (NIH) · 2018
Diagnosing a cortisol disorder requires history, exam and lab tests; no one test is perfect, so doctors usually use two; cortisol normally drops at night.
- Source [25]
Nieman et al., 2008
Read the source (opens in a new tab)The diagnosis of Cushing's syndrome: an Endocrine Society Clinical Practice Guideline
Journal of Clinical Endocrinology and Metabolism · 2008
People with an abnormal first cortisol test should see an endocrinologist and have a second test before any diagnosis.
- Source [26]
Temple et al., 2017
Read the source (opens in a new tab)The Safety of Ingested Caffeine: A Comprehensive Review
Frontiers in Psychiatry · 2017
Caffeine peaks in saliva about 45 minutes and in serum about 2 hours after ingestion, and has a half-life of 3 to 7 hours in adults; oral contraceptives tend to double the half-life, it is longer during pregnancy, and smoking doubles the rate of caffeine clearance.
- Source [27]
FDA, 2024
Read the source (opens in a new tab)Spilling the Beans: How Much Caffeine is Too Much?
U.S. Food and Drug Administration · 2024
For most adults the FDA has cited 400 mg a day as an amount not generally associated with negative effects, with wide variation in how sensitive people are and how fast they eliminate caffeine; typical 12 fl oz amounts: brewed coffee 113 to 247 mg, black tea 71 mg, green tea 37 mg, caffeinated soft drink 23 to 83 mg, energy drink 41 to 246 mg; decaf coffee typically has 2 to 15 mg per 8 fl oz.
- Source [28]
CDC, 2024
Read the source (opens in a new tab)About Sleep
Centers for Disease Control and Prevention · 2024
Recommended sleep by age: adults 18 to 60 years, 7 or more hours; 61 to 64 years, 7 to 9 hours; 65 years and older, 7 to 8 hours.
- Source [29]
Van Dongen et al., 2003
Read the source (opens in a new tab)The cumulative cost of additional wakefulness: dose-response effects on neurobehavioral functions and sleep physiology from chronic sleep restriction and total sleep deprivation
Sleep · 2003
In healthy adults, 14 nights restricted to 6 hours or less in bed produced cumulative cognitive deficits equivalent to up to 2 nights of total sleep deprivation, while sleepiness ratings suggested participants were largely unaware of the growing deficits.
- Source [30]
NIH ODS, 2025
Read the source (opens in a new tab)Ashwagandha: Is it helpful for stress, anxiety, or sleep? Fact Sheet for Health Professionals
Office of Dietary Supplements (NIH) · 2025
Trials gave ashwagandha extracts once or twice daily, usually for 6 to 12 weeks; common side effects are mild (stomach upset, loose stools, nausea, drowsiness); rare liver injury and thyroid effects are reported; might interact with thyroid, diabetes, blood pressure, immunosuppressant and sedative medicines; Denmark banned ashwagandha in 2023.
- Source [31]
NCCIH, 2023
Read the source (opens in a new tab)Ashwagandha: Usefulness and Safety
National Center for Complementary and Integrative Health (NIH) · 2023
Ashwagandha may be safe short term (up to 3 months); long-term safety is unknown; it may cause drowsiness, stomach upset, diarrhea and vomiting; it should be avoided in pregnancy and breastfeeding; rare liver injury has been linked to supplements.
- Source [32]
Cheah et al., 2021
Read the source (opens in a new tab)Effect of Ashwagandha (Withania somnifera) extract on sleep: a systematic review and meta-analysis
PLoS One · 2021
Five randomized trials, all in India, 400 adults: a small but significant overall effect on sleep versus placebo, larger in people with insomnia, at 600 mg a day or more and over 8 weeks or longer; mental alertness on rising also improved; no serious adverse events were reported.
- Source [33]
Langade et al., 2019
Read the source (opens in a new tab)Efficacy and safety of Ashwagandha (Withania somnifera) root extract in insomnia and anxiety: a double-blind, randomized, placebo-controlled study
Cureus · 2019
60 adults with insomnia took 300 mg of root extract or placebo twice daily with milk or water for 10 weeks; sleep onset latency fell to 29.0 minutes versus 34.0 on placebo, sleep efficiency and PSQI improved, and no adverse events were reported.
- Source [34]
Salve et al., 2019
Read the source (opens in a new tab)Adaptogenic and anxiolytic effects of Ashwagandha root extract in healthy adults: a double-blind, randomized, placebo-controlled clinical study
Cureus · 2019
60 stressed but otherwise healthy adults took 250 or 600 mg a day of root extract or placebo for 8 weeks, after food with milk or water; self-rated sleep quality improved and serum cortisol was lower at 8 weeks in both dose groups, with anxiety scores better than placebo only at 600 mg.
- Source [35]
Björnsson et al., 2020
Read the source (opens in a new tab)Ashwagandha-induced liver injury: a case series from Iceland and the US Drug-Induced Liver Injury Network
Liver International · 2020
Five people who took 450 to 1,350 mg of ashwagandha a day for 1 week to 4 months developed liver injury; all improved after stopping.
- Source [36]
Sharma et al., 2018
Read the source (opens in a new tab)Efficacy and safety of Ashwagandha root extract in subclinical hypothyroid patients: a double-blind, randomized placebo-controlled trial
Journal of Alternative and Complementary Medicine · 2018
In adults with subclinical hypothyroidism, 300 mg of root extract twice daily for 8 weeks lowered TSH and raised T3 and T4 compared with placebo.
- Source [37]
Hidese et al., 2019
Read the source (opens in a new tab)Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults: a randomized controlled trial
Nutrients · 2019
30 healthy adults took 200 mg of L-theanine or placebo before sleep each night for 4 weeks in a crossover trial; sleep latency, sleep disturbance and sleep-medication scores improved more than on placebo, the total sleep score did not differ from placebo, and salivary and serum cortisol did not change.
- Source [38]
Bulman et al., 2025
Read the source (opens in a new tab)The effects of L-theanine consumption on sleep outcomes: a systematic review and meta-analysis
Sleep Medicine Reviews · 2025
19 randomized trials (897 participants): L-theanine was associated with small improvements in self-rated sleep onset, daytime dysfunction and overall sleep quality.
- Source [39]
Owen et al., 2008
Read the source (opens in a new tab)The combined effects of L-theanine and caffeine on cognitive performance and mood
Nutritional Neuroscience · 2008
In 27 healthy adults, 50 mg of caffeine plus 100 mg of L-theanine improved accuracy on an attention-switching task at 60 minutes compared with caffeine alone; caffeine alone raised self-rated alertness versus placebo, the combination did not significantly.
- Source [40]
Giesbrecht et al., 2010
Read the source (opens in a new tab)The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness
Nutritional Neuroscience · 2010
In 44 young adults, 97 mg of L-theanine plus 40 mg of caffeine improved attention-switching accuracy and self-rated alertness and lowered tiredness versus placebo; a regular cup of tea contains about 35 to 61 mg of caffeine and 4.5 to 22.5 mg of L-theanine.
- Source [41]
van der Pijl et al., 2010
Read the source (opens in a new tab)Human disposition of L-theanine in tea or aqueous solution
Journal of Functional Foods · 2010
In 15 young men, L-theanine from tea or water reached its peak in blood about 50 minutes after drinking, with an elimination half-life of about 65 minutes.
- Source [42]
NCCIH, 2025
Read the source (opens in a new tab)“Detoxes” and “cleanses”: what you need to know
National Center for Complementary and Integrative Health (NIH) · 2025
Only a small number of studies have looked at detox programs in people, and they were generally low quality; some programs can be unsafe or falsely advertised; regulators have acted against several companies selling detox products.
- Source [43]
Hill et al., 2008
Read the source (opens in a new tab)Exercise and circulating cortisol levels: the intensity threshold effect
Journal of Endocrinological Investigation · 2008
In 12 trained men, 30 minutes of exercise at 60% and 80% of maximal oxygen uptake raised blood cortisol by about 40% and 83%; 40% did not significantly raise it, and after correcting for plasma volume, low intensity lowered it.
- Source [44]
Ng et al., 2025
Read the source (opens in a new tab)Hyperkalaemic cardiac arrest due to cream of tartar ingestion
Medical Journal of Australia · 2025
A woman who swallowed a large amount of cream of tartar as a home remedy developed dangerously high blood potassium and cardiac arrest; 100 g of cream of tartar contains 16.5 g of potassium.
- Source [45]
NIH ODS, 2021
Read the source (opens in a new tab)Potassium: Fact Sheet for Consumers
Office of Dietary Supplements (NIH) · 2021
Adults are advised 2,600 mg (women) or 3,400 mg (men) of potassium a day; orange juice is a listed source; food potassium is not shown to harm healthy people with normal kidneys, but people with kidney disease, or taking ACE inhibitors, ARBs or potassium-sparing diuretics, can develop high blood potassium.
- Source [46]
FDA, 2024
Read the source (opens in a new tab)Voluntary sodium reduction goals (Edition 2): guidance for industry
U.S. Food and Drug Administration · 2024
The Dietary Guidelines advise people aged 14 and older to limit sodium to 2,300 mg a day; salt is 39% sodium by weight.
- Source [47]
Lin et al., 2011
Read the source (opens in a new tab)Effect of kiwifruit consumption on sleep quality in adults with sleep problems
Asia Pacific Journal of Clinical Nutrition · 2011
24 adults with self-reported sleep problems ate two kiwifruit 1 hour before bed for 4 weeks; diary sleep onset fell from 34.3 to 20.4 minutes and diary total sleep time rose from 354.5 to 395.3 minutes; on actigraphy, total sleep time and efficiency rose but sleep onset and night waking changes were not significant.
- Source [48]
Kanon et al., 2023
Read the source (opens in a new tab)Acute effects of fresh versus dried Hayward green kiwifruit on sleep quality, mood, and sleep-related urinary metabolites in healthy young men with good and poor sleep quality
Frontiers in Nutrition · 2023
In 24 young men, a single evening serving of dried kiwifruit powder improved morning sleepiness, alertness on waking and vigor versus water; fresh kiwifruit mostly showed trends.
- Source [49]
Howatson et al., 2012
Read the source (opens in a new tab)Effect of tart cherry juice (Prunus cerasus) on melatonin levels and enhanced sleep quality
European Journal of Nutrition · 2012
In 20 healthy adults, 30 mL of tart cherry concentrate twice a day for 7 days raised urinary melatonin and increased actigraphy total sleep time to about 419 minutes versus about 380 on placebo, with less daytime napping.
- Source [50]
Mah & Pitre, 2021
Read the source (opens in a new tab)Oral magnesium supplementation for insomnia in older adults: a systematic review and meta-analysis
BMC Complementary Medicine and Therapies · 2021
Three trials in 151 older adults, 320 to 729 mg of magnesium a day as oxide or citrate for 20 days to 8 weeks: sleep onset was 17.4 minutes shorter than placebo; total sleep time was not significantly different.
- Source [51]
NIH ODS, 2021
Read the source (opens in a new tab)Magnesium: Fact Sheet for Consumers
NIH Office of Dietary Supplements · 2021
Adults need 310 to 420 mg a day; supplements should stay within 350 mg a day for adults (the limit excludes food); high supplement intakes can cause diarrhea, nausea and cramping; aspartate, citrate, lactate and chloride forms are more easily absorbed; supplements can interact with some medicines.
- Source [52]
Yamadera et al., 2007
Read the source (opens in a new tab)Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes
Sleep and Biological Rhythms · 2007
In volunteers with ongoing unsatisfying sleep, 3 g of glycine before bed improved self-rated sleep quality, shortened time to sleep onset and to slow-wave sleep on polysomnography, and reduced daytime sleepiness.
- Source [53]
Bannai et al., 2012
Read the source (opens in a new tab)The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers
Frontiers in Neurology · 2012
In 7 analysed men whose sleep was cut by 25% for three nights, 3 g of glycine before bed reduced fatigue and improved reaction time on the first day; sleepiness only showed a trend.
- Source [54]
Stutz et al., 2019
Read the source (opens in a new tab)Effects of evening exercise on sleep in healthy participants: a systematic review and meta-analysis
Sports Medicine · 2019
Across 23 studies, evening exercise did not harm sleep and slightly increased slow-wave sleep; the exception was vigorous exercise ending one hour or less before bed, which might impair sleep onset, total sleep and efficiency.
- Source [55]
Bell et al., 2023
Read the source (opens in a new tab)Integrating deloading into strength and physique sports training programmes: an international Delphi consensus approach
Sports Medicine - Open · 2023
Coaches agreed a deload is a planned period of reduced training stress to lower physical and psychological fatigue and promote recovery, most often by cutting sets and reps; they also agreed scientific studies on deloading are limited.
- Source [56]
Badrick et al., 2008
Read the source (opens in a new tab)The relationship between alcohol consumption and cortisol secretion in an aging cohort
Journal of Clinical Endocrinology and Metabolism · 2008
In 3,670 older civil servants, men's cortisol rose about 3% per weekly unit of alcohol, and heavy drinkers had a flatter daytime cortisol decline.
- Source [57]
Martens et al., 2010
Read the source (opens in a new tab)Effects of single macronutrients on serum cortisol concentrations in normal weight men
Physiology & Behavior · 2010
In 10 men, a carbohydrate lunch shake raised cortisol over 3 hours compared with water, while protein and fat shakes did not differ from water.
- Source [58]
Balban et al., 2023
Read the source (opens in a new tab)Brief structured respiration practices enhance mood and reduce physiological arousal
Cell Reports Medicine · 2023
In a remote one-month trial, 5 minutes a day of breathwork, especially cyclic sighing with long exhales, improved mood and lowered resting breathing rate more than the same time spent in mindfulness meditation.
- Source [59]
Laborde et al., 2022
Read the source (opens in a new tab)Effects of voluntary slow breathing on heart rate and heart rate variability: a systematic review and a meta-analysis
Neuroscience and Biobehavioral Reviews · 2022
Across 223 studies, voluntary slow breathing increased vagally mediated heart rate variability during the practice, right after a single session and after multi-session programs.
- Source [60]
Ekholm et al., 2020
Read the source (opens in a new tab)A randomized controlled study of weighted chain blankets for insomnia in psychiatric disorders
Journal of Clinical Sleep Medicine · 2020
In 120 adults with insomnia and depression, bipolar disorder, anxiety or ADHD, an 8 kg chain blanket for 4 weeks led to a 50% drop in insomnia score in 59.4% of users versus 5.4% with a light control blanket; wrist actigraphy showed no significant sleep changes.
- Source [61]
Dutta et al., 2025
Read the source (opens in a new tab)Efficacy of yoga nidra in managing sleep disorders: a systematic review of randomized controlled trials
Journal of Integrative and Complementary Medicine · 2025
Six randomized trials with 244 participants mostly reported better sleep onset, total sleep and sleep efficiency with yoga nidra; the authors call it promising but say high-quality trials are needed.
- Source [62]
Rhee et al., 2025
Read the source (opens in a new tab)Breaking social media fads and uncovering the safety and efficacy of mouth taping in patients with mouth breathing, sleep disordered breathing, or obstructive sleep apnea: a systematic review
PLOS ONE · 2025
Across 10 studies with 213 people, 8 found no evidence that mouth taping helps mouth breathing, sleep-disordered breathing or sleep apnea; 2 suggested slight improvement in some people with mild sleep apnea; 4 described an asphyxiation risk with significant nasal obstruction.
- Source [63]
MedlinePlus, 2024
Read the source (opens in a new tab)Autonomic Nervous System Disorders
National Library of Medicine (NIH) · 2024
The autonomic nervous system controls involuntary actions such as heartbeat and blood vessel width; disorders of it can occur alone or with diseases such as diabetes or Parkinson's, and cause problems with blood pressure, heart, breathing and swallowing.
- Source [64]
Cleveland Clinic, 2022
Read the source (opens in a new tab)Autonomic Nervous System
Cleveland Clinic · 2022
The sympathetic branch drives the fight-or-flight response, the parasympathetic branch handles rest-and-digest processes, and the enteric branch manages digestion.
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