How Circadian Rhythms affect ADHD, and Vice Versa

There are many people affected by having such a misaligned internal clock, but it’s all the more common for people with ADHD. It’s not just occasional either, it’s persistent… a daily battle at night telling yourself it’s time to go to bed, or trying to fall asleep instead of ruminating if you do go to bed earlier, and then in the morning you feel like you’ve barely slept. Then comes tiredness, which exacerbates existing ADHD challenges, while reducing ADHD-related strengths.

There are reasons why people with ADHD experience this more. It’s a deep biological mechanism, all to with the circadian rhythm.

I was discussing this with my research supervisor, who mentioned that it relates to one of the reasons why neurodivergence like ADHD even exists. When viewed through an evolutionary lens, the advantages become clear (London Psychiatry Clinic, n.d.). His own example, which fits well with the general consensus in evolutionary psychology (Evolution and ADHD, 2024) was as follows:

“When most of the prehistoric group were sitting down to warm themselves by the fire, regaling the day’s activities to the others… some members were still needed be on guard and patrol the area, remaining alert to the sabre-tooth tiger… survival depended on diversity for all sorts of things, including timings of sleep and wakefulness” – Prof Brian Garrod

There’s been plenty of research inline with that (discussed and referenced below), including how Circadian Rhythms affect far more than just sleep. And some of this research shows other links between the internal timing system and ADHD. Having an understanding of this, may even provide a few ways to ease some of the everyday struggles people with ADHD face.

Understanding Circadian Rhythms and Chronotypes

Circadian rhythms are 24-hour(ish) biological cycles which regulate a wide array of physical and mental functions. Most of us associate them with sleep, but they actually influence much more, such as hormone levels, body temperature, blood pressure, digestion, immune function, and even when we’re best at thinking or problem-solving (Lunsford-Avery et al., 2024).

These rhythms are driven by a “master clock” in the brain. It’s called the suprachiasmatic nucleus, or SCN, and is located in the hypothalamus. The SCN synchronises all the individual clocks found in virtually every cell of the body (yes, every cell has its own little clock too!). Think of it like the Greenwich Meridian, in relations to people’s watches and the times showing on their smart phones. Just like the Greenwich Meridan, the SCN keeps time using input from the positioning of the Earth and Sun, in other words – from light.

When light hits particular, specialised cells in your eyes, it tells the SCN whether it’s day or night, which helps to reset your internal rhythm accordingly. But light isn’t the only cue. The SCN is impacted by other environmental factors too, including meal times, exercise, and even social interactions – all of which can shift these rhythms slightly. When these cues are misaligned (e.g. during jet lag) problems like poor sleep, grogginess, and impaired focus can arise. This misalignment will commonly affect people with ‘late chronotypes’ (Coogan & McGowan, 2017).

Chronotypes are differences in how people experience these rhythms. The term itself refers to your body’s natural preference for when you sleep, wake, and function best. Morning people (AKA ‘Larks’) feel alert early in the day, while evening people (AKA ‘Owls’) thrive later, but the majority of people tend to fall somewhere in the middle (Coogan & McGowan, 2017).

A person’s chronotype is shaped by genetics, age, and environment. For example, children often lean towards morningness, shift dramatically to eveningness during adolescence, and then gradually back to earlier again as they get older. Seasonal light changes and geography also play a role in this, where bedtimes will be later if the Sun is still out. But more recently, wearable tech and behavioural analysis has provided data that’s been used to work out some of the differences between people’s chronotype – however, this data will be skewed by social demands… including alarm clocks! (Vetter, 2020).

If you are ADHD, you’ll know exactly how this connects together – because you’ll very likely be an ‘Owl’ who keeps trying to get better at being a ‘Lark’. In other words, people with ADHD very commonly have late chronotypes (Coogan & McGowan, 2017), or even extra-late chronotypes – and late chronotypes aren’t well suited to the hours of wakefulness that modern society demands. Research shows that people with ADHD may have different rhythms for cognitive performance, physical activity, and sleep – all of which makes the whole chronotype concept more complex than previously understood (Lunsford-Avery et al., 2024).

ADHD and Sleep

Lots of studies show that sleep issues are far more common in people with ADHD than in the general population. Up to 80% of adults with ADHD and over half of children report sleep disturbances, compared to around 25% in control groups (Bijlenga et al., 2019; Coogan & McGowan, 2017).

The most common problems are:

• Difficulty falling asleep (often due to racing thoughts)
• Night-time awakenings (thoughts again usually, waking us up)
• Restless sleep (thoughts while we sleep, stopping us from going into properly deep (NREM) sleep)
• Waking ‘unrefreshed’, or worse, with sleep inertia (extreme morning grogginess)

There’s also a recurring pattern described as “perverse sleep”, which is being wide awake at bedtime, and very sleepy at points during the day. All of this points to circadian misalignment rather than just poor sleep hygiene (Lunsford-Avery et al., 2018). Although it could of course be a combination in some cases – We don’t help ourselves by never sticking to a routine of going to bed when we should.

One study found 29% of adults with ADHD were definite evening types, compared to just 16% of controls (Bijlenga et al., 2019). In children, the picture is nuanced: some show a general evening preference, but the strongest links between chronotype and symptom severity emerge within ADHD populations (Lunsford-Avery et al., 2024).

Researchers have identified several overlapping mechanisms:

• Genetic overlap: Circadian genes like BMAL1 and PER2 have been implicated in both ADHD and sleep timing disorders (Coogan & McGowan, 2017).
• Light sensitivity: Some with ADHD show increased sensitivity to evening light, which can delay melatonin production (Arns et al., 2013).
• Dopamine regulation: Disrupted dopamine function (central to ADHD) also plays a role in circadian rhythm regulation (Bijlenga et al., 2019).
• Arousal systems and HPA axis: Both systems link to alertness, sleep regulation, and ADHD symptoms (Lunsford-Avery et al., 2024).

This misalignment may lead to a biological “social jetlag”. It results in a mismatch between internal time and societal demands, which then contributes to cognitive disengagement, executive dysfunction, and even mood symptoms (Fredrick et al., 2022; Lunsford-Avery et al., 2024). Note the keyword there ‘contributes‘. It is not a suggestion that this is the cause of ADHD (it isn’t), but something which affects existing symptoms.

And the consequences go beyond feeling tired. Cognitive impairments often associated with ADHD, like inconsistent focus and continuous, prolonged lapses in attention, are worsened by on-task sleepiness, which basically means drowsiness during tasks that require significant brain activity (Lunsford-Avery et al., 2018).

EEG studies have shown increased ‘slow-wave‘ activity in people with ADHD, which implies an overlap between cognitive ‘under-arousal‘ and sleepiness (Coogan & McGowan, 2017). This is something that will often be misinterpreted as lack of motivation or laziness, when in fact it reflects a biologically driven mismatch between brain state and external demands.

Chronotherapy

There’s a growing number of treatments options for misaligned circadian rhythm. They’re collectively named ‘chronotherapeutic interventions‘. Here’s a brief overview:

• Melatonin supplementation: Melatonin has been shown to reduce sleep onset latency and help shift the circadian phase earlier, particularly in kids and adolescents with ADHD. However, its effect on core ADHD symptoms doesn’t seem to have had much impact to-date (Van der Heijden et al., 2005; Bondopadhyay et al., 2022).
• Light therapy: Timed morning exposure to bright light can help regulate the circadian system. Trials in adults with ADHD have shown reduced symptoms following light therapy (Coogan & McGowan, 2017). But take ‘reduced’ with a pinch of salt there, it’s not the easiest of things to measure and there are many other variables that come into play.
• Activity scheduling: Aligning demanding tasks with periods of peak alertness can improve performance. Which is great, but would require flexibility from work or school to levels they’re highly unlikely to be able to offer (Lunsford-Avery et al., 2024).
• Rethinking medication timing: We’ve all been here – meds that won’t let you sleep should not be taken before bedtime. Researchers suggest it’s best to tailor stimulant or non-stimulant timing to align with individual chronotypes (Lunsford-Avery et al., 2024).
• Wearable technology: There are some relatively new developments in the shape of wearable ‘heat flux sensors’ which measure your core body temperature, and improved ‘actigraphy’ – which measures activity levels (like many phones and smart watches do already, just better) allow for some assessment of each everyone’s circadian alignment (Mendt et al., 2017; Lunsford-Avery et al., 2024). These could also help differentiate between causes… whether sleep problems are behavioural, biological, or both.
• Sleep hygiene: This is a big one, really… while consistent bedtimes aren’t going to work as any kind of a ‘cure’, they can and will help to alleviate some symptoms but enough of an amount that it can improve how we feel day-to-day.
  • Easier said that done, because keeping the motivation and discipline to stick to this (against our nature) is difficult to keep front of mind when needed. As anyone with ADHD knows, setting alarms or notifications doesn’t help much, because seconds after acknowledging them and the required actions, you’ve gotten distracted by something again anyway.
  • Even when you are conscious of the time, trying to argue with yourself on whether you should go to bed each night is pitting the delayed gratification of tomorrow’s reward against whatever dopamine chasing is happening at present. What’s needed here is a ‘routine-maker’ with built in incentives, something to help win that daily argument by tilting things in favour of going to bed now.
  • But that’s if your thoughts will let you sleep at bedtime, anyway – which depends not just on routine but whatever else is going on in your life at the time.

Regardless of the above, one thing is clear – the first step towards finding solutions is understanding each of our own circadian biology, so that we can begin to reshape our environments to work with, not against, our body’s natural rhythms. For us with ADHD, this could mean more than improved sleep, it could also mean a boost to better focus, fewer misunderstandings, and a stronger foundation for our strengths around creativity, innovation, and thought exploration.

References

• Bijlenga, D., Vollebregt, M. A., Kooij, J. J. S., & Arns, M. (2019). The role of the circadian system in the etiology and pathophysiology of ADHD: Time to redefine ADHD? ADHD Attention Deficit and Hyperactivity Disorders, 11(1), 5–19. https://doi.org/10.1007/s12402-016-0214-5
• Bondopadhyay, S., Fredrick, J. W., & Gruber, R. (2022). Sleep and ADHD: Research review and clinical update. Journal of Child Psychology and Psychiatry, 63(2), 121–140.
• London Psychiatry Clinic (n.d.). Hunter-gatherers to modern Biohackers: Understanding Neurodivergence. https://www.londonpsychiatry.clinic/blog/hunter-gatherers-to-modern-biohackers#:~:text=According%20to%20a%20landmark%20study,they%20provided%20a%20survival%20advantage.&text=Imagine%20the%20advantage%20these%20traits,zeroes%20in%20on%20moving%20prey.
• Coogan, A. N., & McGowan, N. M. (2017). A systematic review of circadian function, chronotype and chronotherapy in attention deficit hyperactivity disorder. ADHD Attention Deficit and Hyperactivity Disorders, 9(3), 129–147. https://doi.org/10.1007/s12402-016-0214-5
• Evolution and ADHD. (2024, March 4). Columbia University Department of Psychiatry. https://www.columbiapsychiatry.org/research/research-areas/child-and-adolescent-psychiatry/sultan-lab-mental-health-informatics/research-areas/evolutionary-psychiatry/evolution-and-adhd#:~:text=In%20the%20context%20of%20hunter,resource%20utilization%20and%20environmental%20navigation.
• Fredrick, J. W., Bondopadhyay, S., & Gruber, R. (2022). Chronotype and cognitive disengagement in youth. Journal of Adolescent Health, 70(2), 275–282.
• Lunsford-Avery, J. R., Davis, J. L., & Willoughby, M. T. (2024). Circadian rhythm dysfunction and clinical heterogeneity in paediatric ADHD: A critical need for innovation in assessment and treatment. JCPP Advances, 5(1), e12281. https://doi.org/10.1002/jcv2.12281
• Lunsford-Avery, J. R., & Kollins, S. H. (2018). Editorial Perspective: Delayed circadian rhythm phase: A cause of ADHD symptoms in adolescence? Journal of Child Psychology and Psychiatry, 59(9), 913–914. https://doi.org/10.1111/jcpp.12941
• Mendt, S., et al. (2017). Circadian assessment using wearable heat flux sensors. Journal of Thermophysiology, 34(4), 245–253.
• Van der Heijden, K. B., Smits, M. G., Van Someren, E. J. W., & Gunning, W. B. (2005). Prediction of melatonin efficacy by pretreatment dim light melatonin onset in children with idiopathic chronic sleep onset insomnia. Journal of Sleep Research, 14(2), 187–194.
• Vetter C. (2020). Circadian disruption: What do we actually mean?. The European journal of neuroscience, 51(1), 531–550. https://doi.org/10.1111/ejn.14255