The body's biological rhythm is more than its sleep schedule: daily energy patterns, mood, immune capacity, metabolism, and stress responses depend greatly on hormonal timing. Cortisol is among the most important of these hormones. Although usually called the “stress hormone,” it also regulates life's basic rhythm as a hormone of awakening, energy, and adaptation. It should rise naturally in the morning, preparing the body biochemically to start the day.

The morning cortisol peak (Cortisol Awakening Response – CAR) is a key marker of a healthy biological clock. Modern life, stress, poor sleep, chronic inflammation, and especially the biological effects of cancer treatment can substantially disrupt it. In patients receiving cancer treatment, cortisol is generally more irregular: the morning rise may weaken, daytime levels fluctuate, and evening levels remain high. This is more than hormonal disruption; it means fatigue, sleep problems, appetite changes, mood swings, and significantly reduced quality of life.

Morning walking is one of the few behavioral interventions affecting the biological clock. Morning light combined with light-to-moderate walking creates a “hormonal resynchronization effect.” Like a medicine, morning walking can therefore regulate circadian timing and cortisol rhythms. For cancer patients, this is particularly valuable: restoring rhythms disrupted by treatment offers strong physical and psychological support.

Cortisol: Daily Rhythm and Basic Biology

Cortisol is released from the adrenal glands' zona fasciculata and controlled by the hypothalamic–pituitary–adrenal (HPA) axis. Stress, infection, inflammation, sleep, and physical activity influence its release. It is incomplete to view it solely as a stress hormone, because cortisol is also a key determinant of the awakening response.

1. CAR (Cortisol Awakening Response): The Morning Peak

Cortisol begins rising approximately 30 minutes before awakening.
It reaches the day's highest level within 30–45 minutes after waking.
This rise provides fundamental biological preparation for daytime energy, cognitive performance, and stress tolerance.

A blunted CAR has been associated with depression, chronic fatigue, impaired immunity, and cancer-related treatment fatigue (CRF).

2. The Daily Cortisol Curve

Morning: High (awakening peak)
Midday: Moderate
Evening: Low
Night: Lowest

Stress, poor sleep, chemotherapy, and inflammation “flatten” this curve. A flattened curve means biological activity lacks rhythm and the body struggles to regulate its stress–rest cycle.

How Does Morning Walking Affect Cortisol Balance?

Exercise may temporarily increase cortisol; this is biologically normal. Regular exercise, however, recalibrates the HPA axis. Morning walking's special effect comes from its timing, creating a synchronizing signal aligned with the biological clock.

1. Effects on the Awakening Peak

May strengthen an irregular CAR.
Keeps the morning cortisol rise within physiological limits.
Provides more stable energy throughout the day.

Clinical studies have shown a “normalizing effect” of morning exercise, particularly in people with disrupted cortisol rhythms.

2. Morning Light + Walking

Morning light at 445–480 nm can suppress melatonin and reset cortisol timing through the SCN (the biological clock center). Walking strengthens this signal considerably.

The biological clock's “start the day” signal becomes clearer.
Melatonin delay decreases and sleep quality improves.
The HPA axis operates more steadily.

3. Psychoneuroimmunological Effects

Morning walking increases prefrontal cortex activity that modulates stress responses, reduces amygdala reactivity, and suppresses unnecessary large cortisol fluctuations.

Reduced inflammatory cytokines (IL-6, TNF-α)
Increased NK (natural killer) cell activity
Normalization of sympathetic–parasympathetic balance

Why Are Cortisol Rhythms Disrupted in Cancer Patients?

The daily cortisol curve is often irregular in cancer patients, reflecting multiple biological and psychological mechanisms. Cancer-related inflammation, sleep disturbances, pain, dietary changes, and direct biochemical treatment effects substantially influence the HPA axis.

1. Chemotherapy and the HPA Axis

Chemotherapy alters the cytokine balance.
Increased IL-1β, IL-6, and TNF-α may flatten cortisol rhythms.
After chemotherapy, the morning cortisol peak weakens in many patients.

2. Immunotherapy and Cortisol

PD-1/PD-L1 and CTLA-4 inhibitors may trigger inflammatory activity affecting cortisol responses through increased autoimmune reactions. Disrupted cortisol–ACTH dynamics have been reported in some patients.

3. Steroid Use

Steroids given with chemotherapy, such as dexamethasone and prednisone:

Suppress endogenous cortisol production.
Temporarily “switch off” the HPA axis.
After steroid withdrawal, cortisol rhythms may struggle to recover.

CRF is closely associated with disrupted cortisol rhythms.

Weak morning peak → low energy
High evening cortisol → poor sleep
Flattened curve → persistent fatigue

Morning walking is considered one of the strongest behavioral approaches to CRF treatment.

A Comprehensive Morning Walking Guide for Cancer Patients

For cancer patients, morning walking is more than physical activity; it is a therapeutic tool for improving biological rhythms. Each patient's program must nevertheless be individualized.

1. Safety Check Before Starting

Postpone walking if fever, infection, leukopenia, or neutropenia is present.
If platelets are < 30,000, limit walking because of fall and bleeding risks.
Soft ground is essential for patients with bone metastases.
Strenuous walking is not recommended with severe anemia (Hb < 8 g/dL).

2. The Best Time to Walk

According to scientific evidence, the optimal window is:

30–90 minutes after waking
Between 07:00–10:00 in the morning
In natural sunlight if possible

3. Duration and Pace

a) Beginners:

10–15 minutes at a gentle pace
3–4 days per week
Add 3–5 minutes each week to reach 30 minutes

b) Intermediate:

5 days per week × 25–30 minutes
Use the breathing-and-talking test to check intensity

c) Patients in good general condition:

150 minutes of moderate walking per week (ACSM/ASCO recommendation)

4. Adjusting Walks Around Treatment Days

A gentle pace in the 24 hours after chemotherapy.
On days with severe nausea, walking time may be reduced by 40%.
Check pulse and blood pressure on steroid days.

5. For Neuropathy, Pain, and Balance Problems

Trainers with nonslip soles
Short steps if balance is impaired
If going outside is not possible, walk circuits indoors for 5-10 minutes

6. Long-Term Effects of Morning Walking

Stronger CAR
Improved sleep quality
Reduced fatigue symptoms
Improved appetite and metabolic balance
Lower chronic stress

V. References

De Nys L, et al. Physical Activity, Cortisol and Sleep. Psychoneuroendocrinology. 2022.
Bower JE, et al. Cortisol Dysregulation in Cancer-Related Fatigue. Brain Behav Immun. 2016.
Kim N, et al. Exercise Timing and Circadian Rhythms. 2023.
Moyers SA, et al. Physical Activity and Cortisol Regulation. 2023.
Huang HP, et al. Home-Based Walking Program in Chemotherapy. Int J Nurs Pract. 2019.
Rogers LQ, et al. Activity and Sleep in Breast Cancer Survivors. 2017.
Vignjević Petrinović S, et al. Stress–Cancer Interaction. Front Physiol. 2023.
ACS/ASCO Exercise Guidelines for Cancer Survivors. 2021.
Rimmele U, et al. Morning Exercise Impact on Stress Response. Sci Rep. 2016.

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Cortisol Imbalance in Cancer Patients: How Does a Morning Walk Help?

Cortisol: Daily Rhythm and Basic Biology