Sleep Isn’t a Secondary Symptom: What the Evidence Says About Sleep and Mental Health
Updated: 1 hour ago
If you deal with anxiety, depression, or ADHD, you may have heard that poor sleep is something that will resolve itself after treatment (particularly in the case of anxiety).
Clinical psychiatric research points the other way: disrupted sleep frequently drives and maintains mental health struggles, rather than trailing behind them.
In a presentation for Columbia Psychiatry, sleep researcher Dr. Philip Gehrman outlined the clinical data: chronic insomnia and circadian disruption regularly precede depressive episodes, spike daytime anxiety, and impair executive function. Even when psychological symptoms begin to lift, leaving sleep unaddressed significantly increases the odds of a remission of symptoms.
The impacts of stabilising your sleep can be profound for your mental health. Almost every disorder in the DMS VII has some mention of sleep disturbance in it's diagnostic criteria. Unlike other diagnostic criteria, sleep is also highly measurable with common wearable and beside devices able to measure sleep length and quality to the minute.
Dr. Philip Gehrman made this point and also pointed to the fact that sleep is quite often easily improved, at little cost and the research points to it being a cost effective and time efficient strategy to not only quickly improve mental health outcomes, though also maintain them. He advocates treating sleep disturbance and especially circadian disruption early in therapy, as it is often a common driver of common symptoms such as anxiety and low mood.
The Two Clocks Running Your Brain
Sleep is governed by two interacting biological systems:
Sleep Pressure (Process S): A chemical drive that builds up for every hour you remain awake, making you physically tired by the end of the day.
The Circadian Clock (Process C): A 24-hour internal rhythm managed by your brain's suprachiasmatic nucleus, calibrated primarily by environmental light.
When these systems fall out of sync, you end up with that familiar, frustrating state: drained all day, yet wired and restless the moment your head hits the pillow.
Foundational Habits To Correct Sleep Disturbance
1. Prioritise Morning Sunlight (Outside, Not Through Glass)
If you only change one habit, make it this one. Light is the primary input your brain uses to set its master clock, and timing is everything.
The habit: Step outside within 30 to 60 minutes of waking. Aim for 10 to 15 minutes on a clear morning, or 20 to 30 minutes if it's overcast. Drink your morning coffee on the porch, eat breakfast outside, or take a quick walk around the block.
Why it matters: Morning sunlight hits specialised cells in your eyes that signal your brain to halt melatonin production and trigger an early, natural rise in cortisol. This clears morning brain fog and starts a biological countdown for melatonin release about 14 to 16 hours later. Crucially, window glass filters out the specific blue-green wavelengths your eyes need to register this signal. Sitting by a closed window or driving to work with the windows up won't cut it—you need direct, unfiltered outdoor light. This also applies to sunglasses.
2. Lock In a Regular Bedtime
Most of us know this one, though it's true what your grandmother told you! Your body’s internal systems run on predictability.
The habit: Pick a realistic target bedtime and keep it consistent across the week, aiming to stay within a 30- to 60-minute window.
Why it matters: Going to sleep at wildly different times keeps your circadian clock in a perpetual state of drift. When your bedtime shifts by two or three hours from night to night, your body cannot anticipate when to lower core body temperature, regulate blood pressure, or release sleep-promoting hormones. That irregular timing fractures sleep architecture, meaning even if you clock eight hours in bed, the quality of that sleep is significantly degraded.
3. Cut Down on Late-Night Screens
The habit: Put away phones, tablets, and laptops at least 30 to 60 minutes before you plan to sleep. Keep the phone out of arm's reach from the bed.
Why it matters: As highlighted in both circadian neuroscience and clinical sleep research, bright artificial light late at night directly suppresses the natural melatonin surge your brain relies on to initiate sleep. Worse, nighttime light exposure shifts your master clock later, tricking your central nervous system into believing it is still daytime. Beyond the light itself, the dopamine loops and emotional reactivity triggered by scrolling, reading news, or answering late emails activate your autonomic nervous system, keeping your brain in an alert, vigilant state when it needs to be down-regulating.
Breaking the Cycle
Many of my clients come to me with poor sleep and circadian disruption. They describe being sleep and often napping during the day only to wake up tired and unable to sleep at night. They also report daytime anxiety and low mood.
Correcting this early in therapy can highlight what symptoms are driven by circadian disruption and insufficient rest. Normally, it takes about a week of waking up at a set time, getting sunlight in the eyes within 30-60 minutes of waking and going to bed at a semi-regular time to reset the internal clock. The clinical timeframe to reset this is actually 3 days, though often life gets in the way, or the mind refuses to comply initially so we allow a week. It is very achievable and I have seen it have a profound impact.
Perfect sleep is not the goal and unrealistic, although getting a semi-regular bed time with morning sunlit is achievable for almost everyone and the science points to it being one of the most impactful and time efficient ways we have to improve our mental health.