Sleep is one of the most researched topics in performance science and one of the most misunderstood in everyday life. Most people know they need more of it. Far fewer understand what actually makes sleep restorative, why so many popular hacks fall short, and what the evidence really says about practical, sustainable improvement.
To cut through the noise, we spoke with Dr Dean Miller a sleep and exercise scientist with a PhD examining sleep and jet lag in elite athletes, and Director of Chase Science Consultancy, where he works with high-performance athletes, shift workers, and military personnel to optimise sleep and recovery. His answers are clear, evidence-based, and refreshingly free of the over-complicated advice that dominates social media.
Whether you're trying to lose weight, perform better, recover faster, or simply stop waking up exhausted, this guide covers what actually matters.
If you've spent years forcing yourself out of bed at 5am and never quite adjusted, there's a biological reason for that. It's called your chronotype essentially, your natural tendency toward being a morning person, an evening person, or somewhere in the middle.
"Chronotype is something that can be managed," Dr Miller explains, "but for evening types, modern society can be quite hard."
Most people shift slightly across their lifespan. Adolescents tend toward late chronotypes which is why teenagers perpetually stay up too late and struggle to wake for school. In adulthood, we typically settle into one direction or the other. Genetics plays a primary role, but environment matters too: swimmers who train at 4am from childhood often develop an early chronotype through conditioning alone.
Can you train yourself to become a morning person?
To some extent. The most effective lever is light. Getting bright light exposure immediately after waking natural sunlight is best, but a bright artificial light works if the sun isn't up moves your body clock earlier over time. Crucially, this only works with consistency. Waking at the same time every day and seeking morning light creates gradual adaptation; waking at wildly different times each day undoes it.
"If you can, work to your chronotype," Dr Miller advises. "If you can't if you have to be up at 5am there are things you can do to manage your body clock. But consistency is the foundation."
The practical takeaway: if you've genuinely tried to become a morning person and it hasn't stuck, you may simply be working against your biology. Structuring your most demanding work into the hours when your body is naturally more alert is a more sustainable approach than fighting the clock every day.
The answer most people have heard eight hours is broadly right, but the nuance matters.
"I would say aim for over seven consistently," Dr Miller says. "If you can do eight, fantastic."
For athletes, the picture is particularly striking. A recent study asked participants how much sleep they felt they needed to feel fully rested. The average answer was 8.2 hours per night yet most were averaging around 6.2 hours. "Only about 3% of them were actually hitting their own benchmark," Dr Miller notes.
What happens when you consistently fall below seven hours?
The effects are wide-ranging. "Any consistent reduction in sleep is associated with worse immune health," Dr Miller explains. "If you sleep poorly the night before your flu vaccination, we know it's going to be less effective. And when we're sleeping less, we're more predisposed to reaching for unhealthy foods because it's impacting those hunger hormones."
There's also a performance trap that most people fall into without realising it. If you consistently sleep five or six hours, your performance will decline but it will decline to a new, lower baseline. Because the degradation is gradual and consistent, you stop noticing it.
"You're not going to notice the decrements because you're doing the same each day," Dr Miller says. "But you are operating at a reduced capacity."
Evidence-based sleep targets: - General population: 7–9 hours - Athletes and high-demand roles: 8–9 hours - Below 7 hours consistently: associated with immune suppression, disrupted hunger hormones, and reduced cognitive and physical performance
Before supplements, gadgets, evening routines, or anything else consistency.
"The most important thing is consistency," Dr Miller says. "We have these 24-hour biological rhythms called circadian rhythms the body clock. These rhythms are quite set to light, and our bodies know when they're winding down for sleep and when they're going to wake up."
Sleeping during the window your body expects to be asleep produces the best quality sleep. Irregular bedtimes sleeping early one night, late the next disrupt that rhythm and compromise quality even when total hours appear adequate.
"Try to have the same bedtime and same wake-up time where possible even on weekends."
The weekend sleep-in is one of the most common ways people inadvertently undermine their sleep quality through the week. Dr Miller's practical compromise: limit any weekend sleep-in to around 90 minutes, which is roughly one full sleep cycle. "You still get that satisfaction of sleeping in, but you don't shift your body clock enough to cause problems come Monday morning."
Light is the primary signal that sets your body clock and most people are getting it backwards.
In the morning: seek light as early as possible after waking. Natural sunlight is optimal, but a bright artificial source works when the sun isn't up. This anchors your circadian rhythm and signals clearly that the day has started.
In the evening: reduce bright, white, or blue-toned light in the lead-up to sleep. This means dimming overhead lights, switching to warmer lamps, and lowering screen brightness.
"We're more sensitive to blue-green light in terms of our body clock," Dr Miller explains. "But even if it's not blue-green if it's just bright white light it's still going to have an impact. Warmer light is better."
What about blue light blocking glasses?
They can work, with a caveat. "The orange-tinted ones that block that blue-green wavelength have scientific support," Dr Miller says. "But you could also just turn off the ceiling lights. It's just another tool."
More importantly, the bigger problem with evening screen use isn't the light itself it's the behaviour. "It's the behavioural aspect of just scrolling and delaying your sleep for an hour. Focus on that first."
Practical light rules: - Morning: bright light exposure within 30–60 minutes of waking - Evening: no bright overhead lights in the hour before bed - Switch to a warm lamp for evening watching or reading - Reduce screen brightness as you move toward bedtime - Blue light glasses can help if you work on screens close to bedtime, but dimming the room is equally effective
Lying in bed with a brain that won't switch off is one of the most common sleep complaints. Work, tomorrow's to-do list, anxiety, replaying conversations the more you try to stop thinking, the louder it gets.
Dr Miller's primary tool: mental gymnastics deliberately occupying the mind with a low-stakes, absorbing task that crowds out the intrusive thoughts.
"I like to go through the alphabet of football players. Usually when I get to R or S, I'm falling asleep. It's just little tactics like that anything that's going to distract you from the things you don't want to think about."
The underlying principle is the same as counting sheep: give your brain something trivial to process, and it stops cycling through everything else.
Other strategies that work:
The worst thing you can do is lie in bed frustrated about not sleeping. If you've been awake for 20 or more minutes and feel wired or anxious, get up, do something calm in dim light reading, gentle stretching and return to bed only when you feel genuinely sleepy.
Wearables and sleep apps place significant emphasis on sleep stages percentages of REM, deep sleep, and light sleep. But should you actually be making decisions based on these numbers?
"Practically, I wouldn't," Dr Miller says plainly. "What I look at is just total sleep time. If you're maintaining a regular bedtime and wake-up time, your body is going to regulate those stages as needed."
The deeper principle: consistent sleep duration and timing naturally produce appropriate sleep architecture. Monitoring stage percentages daily tends to create anxiety that paradoxically makes sleep worse particularly for people who already struggle to switch off.
"Consistency and duration is going to help with quality and sleep staging," Dr Miller explains. "If you do see a drastic change in how a device is reporting your sleep staging, it may indicate something else is changing in your physiology you might be getting sick, or going through a high training load period."
What to track instead of sleep stages: - Total sleep time" are you consistently hitting 7–9 hours? - Consistency: are you going to bed and waking at the same times? - Subjective feel: do you wake feeling rested, regardless of what the app says?
Consumer sleep trackers have become ubiquitous but how much should you trust what they're telling you?
Dr Miller has run studies directly comparing wearable data against polysomnography (PSG), the gold standard of sleep measurement, which uses electrodes to track actual brain wave activity.
"Most commercially available sleep devices are great for measuring sleep and wake the total amount of sleep," he confirms. "The difficulty is with sleep staging, particularly detecting brief awakenings within sleep that you might not even realise are happening."
Gold standard lab measurement achieves around 80% accuracy for sleep staging. The best consumer wearables sit at roughly 65% good, but not lab-grade.
"I would focus on what these devices are reliably good at: total sleep time, resting heart rate, and heart rate variability. Not on making daily decisions based on sleep stage percentages."
On heart rate variability (HRV):
HRV: the variation in time between heartbeats reflects how well your autonomic nervous system has recovered. Higher HRV relative to your own baseline generally suggests better recovery. But it is highly individual: Dr Miller has seen elite athletes with comparatively low HRVs and everyday people with high ones.
"It's really important to just compare to your own baseline rather than compare across individuals. I could have an HRV of 100 and you could have an HRV of 50 that doesn't mean I'm healthier or more recovered than you."
How to use wearable data well: - Focus on trends over weeks, not single-day readings - A low recovery score on a day you feel great doesn't mean you can't perform. Dr Miller has seen athletes set personal bests after terrible nights of data - A high recovery score doesn't mean you should ignore signals from your own body - Use the data as one input, not the final word
Poor sleep doesn't just make you tired it directly disrupts the hormones that regulate hunger and food behaviour.
"When we're sleeping less, we're more predisposed to reaching for unhealthy foods because it's impacting those hunger hormones," Dr Miller explains.
Research consistently shows that sleep deprivation elevates ghrelin (the appetite-stimulating hormone) and suppresses leptin (the fullness signal). The result is predictable: you eat more, feel less satisfied by what you eat, and the foods you crave tend to be calorie-dense.
For anyone in a weight loss phase, this creates a compounding problem. Sleep restriction degrades the hormonal environment that supports fat loss making an already demanding process significantly harder to maintain. "It sort of just rolls on to basically most physiological processes," Dr Miller says.
This is one of the reasons that having your nutrition structured and automated through tools like INCHECK FIT works best when sleep is treated as part of the equation. A calibrated meal plan and appropriate calorie targets are considerably more effective when your hunger and fullness signals are functioning normally which is fundamentally dependent on consistent, quality sleep.
The sleep–weight connection in practical terms: - Under 7 hours of sleep → elevated ghrelin, suppressed leptin - Poor sleep → increased cravings for high-calorie, energy-dense foods - Chronic sleep restriction → metabolic disruption and reduced fat loss even within a caloric deficit - Improving sleep quality is one of the highest-leverage, lowest-cost changes a person in a weight loss phase can make
"The best advice I've heard for shift workers is: quit your job and get a new one," Dr Miller says. "But obviously that's not realistic for most people."
Managing sleep as a shift worker comes down to understanding two core biological systems:
1. Sleep pressure (adenosine)
From the moment you wake, a molecule called adenosine accumulates in the brain. The longer you're awake, the more it builds. The only way to clear it is sleep. Caffeine works by blocking adenosine receptors temporarily masking fatigue without eliminating it. For shift workers, this makes caffeine timing critical: use it strategically, a few hours into a night shift when fatigue is peaking, rather than immediately at the start when you're not yet tired.
2. The body clock (circadian rhythm)
Your circadian rhythm runs on approximately a 24-hour cycle and is primarily set by light. Three to four consecutive night shifts is typically enough to shift your body clock into night-phase alignment. A single night shift isn't which means the advice differs depending on how regularly you're on nights.
For long-term night workers, the key tactics are: keep the sleep environment dark and cool, seek light at the times that will support your new rhythm, and accept that the toughest period is likely the weekend when social pressures conflict with your body clock.
The caffeine nap a practical tool for shift workers:
Have a coffee immediately before a 20-minute nap. Caffeine takes roughly 20 minutes to absorb, so by the time you wake, it's beginning to take effect eliminating the post-nap grogginess (sleep inertia) while still getting the restorative benefit of the nap itself.
General napping guidance: - Keep naps to 20–30 minutes to avoid entering deep sleep - Before 4pm where possible, to avoid disrupting nighttime sleep - Longer naps are appropriate during periods of high training load or shift work, where total sleep time needs to be made up
Melatonin is probably the most commonly misunderstood sleep supplement on the market.
"Your melatonin is a naturally occurring hormone," Dr Miller explains. "It kicks in about two hours before you'd usually go to bed. Supplements are essentially the synthetic form of it."
Used correctly, melatonin can meaningfully support: - Falling asleep (mild hypnotic effect) - Jet lag recovery (when timed correctly) - Acute sleep disruption (illness, travel, time zone shifts)
The critical caveat: timing matters enormously and getting it wrong can make things worse.
"If you take melatonin at the wrong time say you wake in the middle of the night and take one it can actually move your body clock in the wrong direction, making the following night worse," Dr Miller says.
Melatonin doesn't just make you sleepy; it also signals your circadian rhythm. Take it at the wrong phase, and you're shifting your body clock in a direction you don't want.
"I would only reach for melatonin if the behavioural boxes are already ticked: consistent sleep schedule, managing light, reducing stimulation before bed and those aren't working."
If you're going to use it: - Take it 1–2 hours before your intended bedtime - Ensure you have nothing to do after taking it - If you're waking up groggy the following morning, speak to your doctor about the dosage - Do not self-prescribe for ongoing sleep problems without medical guidance, seek a GP with sleep expertise, or a sleep specialist.
Jet lag is a misalignment between your internal body clock and the time zone you're in and the primary tool to resolve it isn't medication. It's light.
"The timing of light exposure is essential, and it changes depending on where you're coming from, where you're going, and how long you're there for," Dr Miller explains.
The general principle: identify the light-exposure window that shifts your body clock in the right direction, and avoid light in the window that would reinforce your old time zone.
"If you get the light and avoid sequence right, you can typically shift your body clock by about two hours per day," Dr Miller says. "For most long-haul trips, that means getting over jet lag in three to four days rather than seven."
Travelling to Europe tends to be more manageable than returning. The afternoon sunlight that comes naturally from sightseeing often happens to work in your favour on the way there. Coming back is a different story.
"When you return from Europe, you're badly situated for jet lag. People typically take close to a week to recover from the return trip."
For short-turnaround trips fly in, fly out Dr Miller's advice is simple: "It's probably not worth doing anything at all. Just get back into your normal rhythm when you're home."
Travel fatigue vs jet lag:
These are two separate issues. Travel fatigue the exhaustion that comes from cabin pressure, dry air, disrupted posture, and prolonged wakefulness is not the same as jet lag. Address it with compression garments on long flights, adequate hydration, avoiding alcohol in the air, and light recovery activity (a walk or pool session) on arrival.
"The nightcap" is one of the most enduring myths in sleep the idea that a drink or two helps you wind down and sleep better.
"It helps you fall asleep faster, but the quality is compromised," Dr Miller says. "It potentially delays some of the restorative stages of sleep."
Alcohol acts on the central nervous system in a way that accelerates sleep onset but disrupts sleep architecture reducing time in REM and slow-wave sleep, the stages most associated with restoration, memory consolidation, and physical recovery. As the sedative effect wears off in the early hours, you're more likely to wake and remain in lighter, less restorative sleep for the rest of the night.
"There is nothing that affects my wearable data more than alcohol," Dr Miller says from his own years of tracking. "Even one drink, I can see it in the data."
The implication isn't necessarily abstinence it's timing and awareness. "Further away from bed, the better," he advises. If you're not ready to cut back, leaving a longer gap between your last drink and sleep will meaningfully reduce the impact on sleep quality.
What is the most important thing I can do to improve sleep quality? According to Dr Dean Miller, the single most impactful change is consistency going to bed and waking at the same time every day, including weekends. This anchors your circadian rhythm and ensures your body is sleeping during the window it expects to be asleep, maximising restorative quality regardless of any other factors.
How many hours of sleep do I actually need? For most adults, seven to nine hours is the evidence-based target. Below seven hours consistently is associated with impaired immune function, disrupted hunger hormones, and reduced cognitive and physical performance. Most people significantly overestimate how well they're functioning on less sleep than they actually need.
How does poor sleep affect weight loss? Sleep deprivation increases ghrelin (the appetite-stimulating hormone) and suppresses leptin (the fullness signal), making you more likely to overeat and crave calorie-dense foods. Consistent poor sleep can actively work against fat loss even when nutrition and training are on track making quality sleep one of the highest-leverage changes for anyone in a weight loss phase.
Are wearables like Whoop and Oura worth using for sleep? Yes, with appropriate expectations. Consumer devices achieve around 65% accuracy for sleep staging (versus roughly 80% in a clinical lab setting) but are reasonably reliable for total sleep time, resting heart rate, and heart rate variability. Focus on trends across weeks rather than single-day readings, and always weigh the data against how you actually feel.
Does exercising at night ruin your sleep? Not necessarily. Dr Miller's research found that moderate-intensity exercise with a 90-minute buffer before bed did not significantly impair sleep quality core body temperature returned to baseline within that window. High-intensity sessions may take longer to recover from. If you train in the evenings, allow at least 90 minutes between finishing your session and getting into bed.
When should I take melatonin for sleep? Approximately one to two hours before your intended bedtime emulating the natural melatonin rise that occurs about two hours before sleep. Taking it at the wrong time (for example, in the middle of the night if you wake up) can shift your body clock in the wrong direction and disrupt the following night's sleep. Only use it after consistent behavioural strategies have been tried, and consult a doctor if considering it for ongoing sleep issues.
How does alcohol affect sleep quality? Alcohol helps you fall asleep faster but significantly reduces sleep quality by suppressing restorative REM and slow-wave sleep. Even one to two drinks close to bedtime can shift you toward lighter, less restorative sleep stages and increase early morning waking. The further from bedtime you drink, the lower the impact on sleep architecture.
How should shift workers approach sleep? The key is understanding both sleep pressure (the adenosine build-up that makes you feel tired) and your body clock (circadian rhythm set by light). Use caffeine strategically during the toughest phase of a night shift rather than at the start; keep the sleep environment dark and cool; and be aware that the most difficult period is often the weekend, when your entrenched night rhythm clashes with normal social life.
Last reviewed: March 2026 by the INCHECK FIT nutrition team.
