Timing is Everything: Circadian Rhythms as a Pillar of Health

At the intersection of circadian science and human health lies a truth too often overlooked: our internal clocks shape nearly every aspect of our biology.

In this piece, co-authored by Dr. Shantha Rajaratnam, Professor of Sleep and Circadian Medicine and a leading global expert on biological rhythms, and Dr. Jonathan Moustakis, medical doctor and co-founder of Lume Health, we explore the powerful role circadian rhythms play in health outcomes, performance, and disease risk.

As Dr. Rajaratnam frequently emphasizes, healthy sleep and circadian timing form the “third pillar” of health, alongside nutrition and physical activity. Together, we’ll draw on decades of research and a shared mission to translate this science into action, illuminating why when you live matters just as much as how you live.

When Circadian Rhythms Fall Out of Sync

Mounting evidence shows that when our circadian rhythms are frequently out of sync, multiple aspects of health can suffer. Researchers are now linking circadian disruption to a startling range of health issues, from metabolic diseases and mood disorders to impaired immunity and even cancer.

• Metabolic Health and Weight: Circadian misalignment has a powerful impact on metabolism. Our bodies evolved to digest food and burn calories during daylight hours, not late at night. When we eat or stay active at biologically inappropriate times, it can throw off metabolic hormones like insulin. Studies indicate that disrupted circadian rhythms (due to factors like shift work, late-night eating, or exposure to light at night) are associated with higher risks of obesity, type 2 diabetes, and metabolic syndrome. For example, one recent review highlighted that night-shift work, irregular meal timing, and nighttime light exposure are all associated with weight gain and poor cardiometabolic outcomes.¹

• Cardiovascular Disease Risk: The stress of operating against our biological clocks can elevate blood pressure and inflammatory markers, contributing to heart disease over time. In fact, shift workers (whose circadian rhythms are chronically disturbed) have higher rates of cardiovascular conditions than non-shift workers.² Over the long term, the accumulation of damage caused by a disrupted biological clock takes a toll. A notable 24-year follow-up study of over 46,000 nurses found that those with long histories of rotating night shifts had significantly lower odds of being relatively healthy at 70 years of age compared to those who never worked night shifts.³ Fewer of the night-shift nurses were free of major chronic diseases by their 70s, suggesting that circadian misalignment accelerated the aging process and development of illness.

• Cancer risk: Even more sobering, the link between circadian disruption and cancer has grown so strong that the World Health Organization’s cancer research arm (IARC) has classified night shift work as “probably carcinogenic to humans”.⁴ The IARC based this 2019 determination on both animal evidence and human studies indicating that disturbances to the light-dark cycle can promote cancer development.

• Mental Health and Cognitive Function: Anyone who has pulled an all-nighter or travelled across time zones knows how this abrupt disruption of circadian rhythms can affect mood and thinking over several days. Research confirms there is a strong two-way relationship between circadian rhythms and mental health. For instance, studies have found that disrupting circadian rhythms, whether through jet lag, shift work, or even exposure to light at night, can precipitate or worsen depressive symptoms in vulnerable people.⁵ Researchers, including Dr. Rajaratnam, have explored how circadian clock disruption might underlie cognitive impairments as well.⁶ There is even emerging evidence tying chronic circadian disruption to a higher risk of neurodegenerative diseases such as dementia over the lifespan.⁷ While this research is still evolving, it underscores that our brain function is tightly intertwined with the rhythms of our internal clock.

This disruption causes damage at a cellular level that, over time, accumulates into diseases ranging from metabolic disorders to cancer and even neurodegenerative disorders. The body simply isn’t designed for living out of sync, particularly in the long term.

In our fast-paced world, it’s easy to ignore the quiet ticking of our biological clocks. But as science continues to show, circadian rhythms influence far more than just sleep- they’re foundational to nearly every aspect of our health. Dr. Rajaratnam often highlights that improving circadian health isn’t just a lifestyle optimization, it’s a neuroscience-based strategy for prevention. When practiced consistently, this approach can lead to improved metabolic health, enhanced mental function, increased emotional resilience, and a reduced risk of chronic disease.

You can begin today. Some of the highest-leverage actions for strengthening your circadian rhythm include:

• Prioritize a Consistent Sleep Schedule: Go to bed and wake up at the same time each day, including weekends. A stable sleep-wake cycle reinforces your body’s natural rhythm.

• Seek Daylight, and ensure Dim Lighting in the evening: Light is the most powerful cue for your master clock. Aim for bright light exposure, particularly in the morning, take your coffee outside, or sit by a sunny window. As evening approaches, dim the lights to signal wind-down time.

When these habits are integrated into your daily routine, the benefits go beyond feeling well-rested. They support your long-term health and well-being, helping not just to add years to your life, but to add life to your years.

Dr. Shanthakumar W. Rajaratnam
Head of School, Psychological Sciences, Monash University

Dr. Jonathan Moustakis
Co-founder and CTO, Lume Health

References

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2. Torquati L, Mielke GI, Brown WJ, Kolbe-Alexander T. Shift work and the risk of cardiovascular disease. A systematic review and meta-analysis including dose-response relationship. Scand J Work Environ Health. 2018 May 1;44(3):229-238. doi: 10.5271/sjweh.3700. Epub 2017 Dec 16. PMID: 29247501.

3. Shi H, Huang T, Schernhammer ES, Sun Q, Wang M. Rotating Night Shift Work and Healthy Aging After 24 Years of Follow-up in the Nurses' Health Study. JAMA Netw Open. 2022 May 2;5(5):e2210450. doi: 10.1001/jamanetworkopen.2022.10450. Erratum in: JAMA Netw Open. 2022 Jun 1;5(6):e2218151. doi: 10.1001/jamanetworkopen.2022.18151. PMID: 35507343; PMCID: PMC9069254.

4. Erren TC, Morfeld P, Groß JV, Wild U, Lewis P. IARC 2019: "Night shift work" is probably carcinogenic: What about disturbed chronobiology in all walks of life? J Occup Med Toxicol. 2019 Nov 27;14:29. doi: 10.1186/s12995-019-0249-6. PMID: 31798667; PMCID: PMC6882045.

5. Walker WH 2nd, Walton JC, DeVries AC, Nelson RJ. Circadian rhythm disruption and mental health. Transl Psychiatry. 2020 Jan 23;10(1):28. doi: 10.1038/s41398-020-0694-0. PMID: 32066704; PMCID: PMC7026420.

6. Ganesan S, Magee M, Stone JE, Mulhall MD, Collins A, Howard ME, Lockley SW, Rajaratnam SMW, Sletten TL. The Impact of Shift Work on Sleep, Alertness and Performance in Healthcare Workers. Sci Rep. 2019 Mar 15;9(1):4635. doi: 10.1038/s41598-019-40914-x. PMID: 30874565; PMCID: PMC6420632.

7. Nassan M, Videnovic A. Circadian rhythms in neurodegenerative disorders. Nat Rev Neurol. 2022 Jan;18(1):7-24. doi: 10.1038/s41582-021-00577-7. Epub 2021 Nov 10. PMID: 34759373.