Sleep is usually the last item on the list, looked at once the training, the eating and the medication are sorted. In our clinic it more often belongs at the other end. Poor sleep is one of the more common explanations we find for why an otherwise sensible plan is underdelivering, which is why we ask about it before escalating anything else.
That is not a wellness claim. It is physiology that has been measured directly, and the measurements are worth knowing.
Dr Samra works through the whole picture in the sleep lecture of our education series: https://www.youtube.com/watch?v=1hpZAgNeQfY
Six nights is enough to move your glucose
Spiegel, Leproult and Van Cauter restricted eleven healthy young men to four hours in bed a night for six nights, then measured the same men again after six nights of twelve hours in bed. Glucose tolerance was lower in the sleep restricted state. Evening cortisol was raised, and sympathetic nervous system activity was increased (Spiegel and colleagues, 1999).
Eleven men is a small study, and four hours a night is more restriction than most people impose on themselves. What it establishes is direction and speed. This is not a slow accumulation across decades. Carbohydrate handling shifts inside a week, worth holding alongside what we have written about individual responses to food.
What the brain does while you are not using it
Sleep is also when the brain clears its own waste. Xie and colleagues showed in mice that natural sleep was associated with roughly a sixty per cent expansion of the interstitial space in the brain, sharply increasing the exchange of cerebrospinal fluid with interstitial fluid and the rate at which beta amyloid was cleared (Xie and colleagues, 2013).
That is animal work, and it should be read as mechanism rather than as a finding about people. So let us be plain: nobody can tell you that better sleep will prevent dementia, and we are not going to. What can be said is that protecting deep sleep is biologically reasonable, at low cost and low risk, with plausible benefit across several systems at once.
Both ends of the curve carry risk
Sleep duration and cardiovascular outcomes do not sit on a straight line. Cappuccio and colleagues pooled fifteen prospective studies covering 474,684 people. Short sleep carried a higher risk of developing or dying from coronary heart disease, at a relative risk of 1.48. Long sleep carried elevated risk too, for coronary heart disease, stroke and total cardiovascular disease (Cappuccio and colleagues, 2011). Yin and colleagues later modelled the dose response across prospective cohorts and found the same U shape, with the lowest risk at around seven hours (Yin and colleagues, 2017). Jin and colleagues found that shape again in a United States cohort, where sleeping under five hours or more than nine hours both carried elevated all cause and cardiovascular mortality against a seven hour reference (Jin and colleagues, 2022).
The two ends mean different things. Persistently short sleep is a cardiometabolic signal worth investigating rather than reassuring, and belongs in the same conversation as the rest of a person's cardiovascular risk picture. Persistently long and unrefreshing sleep usually points at something underneath it. The American Academy of Sleep Medicine and the Sleep Research Society recommend adults sleep at least seven hours a night on a regular basis (Watson and colleagues, 2015).
Hours in bed is not the same as sleep
Duration is the easy number, not the whole measurement. Deep sleep dominates the early cycles and carries most of the physical repair. Rapid eye movement sleep lengthens towards morning and carries most of the emotional and cognitive work. A night broken by arousals you never notice loses disproportionately from both, even when the time in bed looks reasonable.
Obstructive sleep apnoea is a common reason for that, and more common than older estimates suggested. In the HypnoLaus study, Heinzer and colleagues ran home sleep studies on 2,121 adults aged 40 to 85 and found moderate to severe sleep disordered breathing in 49.7 per cent of men and 23.4 per cent of women. Higher indices were independently associated with hypertension, with diabetes, and with metabolic syndrome (Heinzer and colleagues, 2015).
Which is why waking unrefreshed, blood pressure that will not come down, or glycaemic drift in an adherent patient are all worth investigating rather than reassuring.
What we do with that
Sleep is assessed the way everything else is assessed: with validated instruments, then read against the rest of the data rather than on its own. Where the history points to sleep disordered breathing, the referral is to a sleep physician. Where the picture is chronic insomnia, the evidence supports cognitive behavioural therapy ahead of a sedative. Trauer and colleagues pooled twenty randomised trials covering 1,162 adults and found time to fall asleep improved by about nineteen minutes and sleep efficiency by about ten per cent, sustained beyond the end of treatment, with no adverse outcomes reported (Trauer and colleagues, 2015).
Within the Exercise Medicine Healthspan Program, sleep is read alongside body composition, cardiorespiratory fitness, strength, glucose, lipids and blood pressure. On its own it is a complaint. Alongside the rest, it is often the explanation.
Next step
If a plan is not delivering and sleep has not been properly examined, that is the least expensive place to look. Speak to your GP about a referral, or get in touch with Progressive Sports Medicine to ask about a comprehensive assessment.
Dr Samra's full lecture on sleep covers each of these mechanisms in depth: https://www.youtube.com/watch?v=1hpZAgNeQfY
The complete education series sits here: https://www.youtube.com/playlist?list=PLS1jg3x2hOTMexo2ieEO8CSYtNXmYNdGj, and new material goes up on our channel: https://www.youtube.com/@ProgressiveSportsMedicine
References
- Spiegel K, Leproult R, Van Cauter E. Impact of sleep debt on metabolic and endocrine function. The Lancet. 1999;354(9188):1435 to 1439. https://doi.org/10.1016/S0140-6736(99)01376-8
- Xie L, Kang H, Xu Q, et al. Sleep drives metabolite clearance from the adult brain. Science. 2013;342(6156):373 to 377. https://doi.org/10.1126/science.1241224
- Cappuccio FP, Cooper D, D'Elia L, Strazzullo P, Miller MA. Sleep duration predicts cardiovascular outcomes: a systematic review and meta analysis of prospective studies. European Heart Journal. 2011;32(12):1484 to 1492. https://doi.org/10.1093/eurheartj/ehr007
- Yin J, Jin X, Shan Z, et al. Relationship of sleep duration with all cause mortality and cardiovascular events: a systematic review and dose response meta analysis of prospective cohort studies. Journal of the American Heart Association. 2017;6(9):e005947. https://doi.org/10.1161/JAHA.117.005947
- Jin Q, Yang N, Dai J, et al. Association of sleep duration with all cause and cardiovascular mortality: a prospective cohort study. Frontiers in Public Health. 2022;10:880276. https://doi.org/10.3389/fpubh.2022.880276
- Watson NF, Badr MS, Belenky G, et al. Recommended amount of sleep for a healthy adult: a joint consensus statement of the American Academy of Sleep Medicine and Sleep Research Society. Journal of Clinical Sleep Medicine. 2015;11(6):591 to 592. https://doi.org/10.5664/jcsm.4758
- Heinzer R, Vat S, et al. Prevalence of sleep disordered breathing in the general population: the HypnoLaus study. The Lancet Respiratory Medicine. 2015;3(4):310 to 318. https://doi.org/10.1016/S2213-2600(15)00043-0
- Trauer JM, Qian MY, Doyle JS, Rajaratnam SMW, Cunnington D. Cognitive behavioral therapy for chronic insomnia: a systematic review and meta analysis. Annals of Internal Medicine. 2015;163(3):191 to 204. https://doi.org/10.7326/M14-2841
