Circadian Rhythm Disruption and PCOS

Polycystic Ovary Syndrome (PCOS) is often framed as a reproductive or metabolic condition. Irregular cycles. Elevated androgens. Insulin resistance. Weight gain. Acne. Infertility.

But step back, and a different pattern starts to emerge.

Many people with PCOS also report poor sleep, delayed sleep timing, difficulty waking in the morning, persistent fatigue, and a sense that their body never quite switches off at night.

Increasingly, PCOS looks less like a single hormonal problem and more like a system-level timing disorder, one where the circadian system (and especially cortisol rhythms) play a central role.

A Quick Reset: What the Circadian System Actually Does

Your circadian rhythm is not just a sleep clock. It’s a 24-hour timing system that coordinates:

• Glucose metabolism

• Steroidogenesis

• Inflammation and immune signalling

• Cortisol release and recovery

In other words, every major hormone involved in PCOS (insulin, cortisol, LH, and  testosterone) all follow circadian regulation (1,2).

When those rhythms are strong and well-timed, physiology runs efficiently.
When they’re flattened, or misaligned, systems begin to interfere with one another.

This brings us to one of the most underappreciated concepts in circadian biology: amplitude.

Circadian rhythms aren’t just about when something happens (phase). They’re also about how much things rise and fall over the day (amplitude).

In practical terms:

• Cortisol should rise sharply in the morning and fall deeply at night

• Glucose tolerance should peak earlier in the day

• Ovarian and adrenal hormone production should follow predictable timing

Multiple studies suggest that people with PCOS show evidence of circadian disruption, including altered sleep timing, reduced rhythm robustness, and abnormal cortisol patterns (3). This matters because cortisol is not just a stress hormone. It’s a regulator of several physiological subsystems.

Cortisol as the Missing Link in PCOS

Cortisol sits at the intersection of circadian biology, metabolism, and reproductive endocrinology.

Here’s why disrupted cortisol rhythms may worsen PCOS:

Cortisol and Insulin Resistance

Chronically elevated or mistimed cortisol reduces insulin sensitivity and increases hepatic glucose production, even independent of body weight. Insulin resistance, in turn, drives excess ovarian androgen production. (4)

Cortisol and Androgen Excess

The adrenal glands contribute significantly to circulating androgens. Dysregulation of the hypothalamic–pituitary–adrenal (HPA) axis has been documented in PCOS and may exacerbate hyperandrogenism (4).

Cortisol and Sleep

Sleep disturbances are more common in PCOS, independent of BMI. Short or delayed sleep further blunts cortisol amplitude, reinforcing circadian misalignment

Cortisol and Inflammation

Flattened cortisol rhythms are associated with elevated baseline inflammation and impaired immune regulation, both of which are frequently observed in PCOS.

Taken together, cortisol is not merely correlated with PCOS. It may act as a physiological amplifier that keeps symptoms entrenched.

The light at the end of the tunnel

If cortisol is the output, light is the input.

Light is the strongest signal your circadian system receives.

Morning light exposure, particularly within the first hour after waking, strengthens signalling from the brain’s master clock to downstream systems, including the HPA axis that regulates cortisol.

Studies suggest that light therapy can improve the signs and symptoms associated with PCOS. (5)

A Different Way to Think About PCOS

PCOS is not only a disorder of hormone levels, but of hormone timing.

Many physiological systems depend on coordinated rises and falls across the circadian cycle. When this temporal organization is disrupted, circadian amplitude is reduced and downstream metabolic and reproductive dysfunction can emerge. If you only remember one thing from this blog, remember that your health is strongly shaped by your light exposure; making it a dimension of PCOS physiology that is at least partially modifiable.

References:

1. Bass, J. and Takahashi, J.S. (2010) ‘Circadian integration of metabolism and Energetics’, Science, 330(6009), pp. 1349–1354. doi:10.1126/science.1195027.

2. Kennaway, D.J. (2005) ‘The role of circadian rhythmicity in reproduction’, Human Reproduction Update, 11(1), pp. 91–101. doi:10.1093/humupd/dmh054.

3. Heydari, T. and Ramdass, P.V.A.K. (2025) ‘Circadian rhythm disruption and polycystic ovary syndrome: A systematic review and meta-analysis’, AJOG Global Reports, 5(2), p. 100479. doi:10.1016/j.xagr.2025.100479.

4. Kodaman, P.H. and Duleba, A.J. (no date) ‘Metabolic and endocrine effects of statins in polycystic ovary syndrome’, Contemporary Endocrinology, pp. 241–258. doi:10.1007/978-1-59745-108-6_15.

5. Chu, W. et al. (2020) ‘Continuous light-induced PCOS-like changes in reproduction, metabolism, and gut microbiota in Sprague-Dawley Rats’, Frontiers in Microbiology, 10. doi:10.3389/fmicb.2019.03145.