Night Shift, Illness, and HRV: What the Data Reveal

By R.E. Hengsterman MSN, MA, M.E., RN

Lately, I haven’t been feeling well. Run down. Tired in a way sleep doesn’t quite fix. I’ve been getting over a recent illness while still working nights, doing what most of us do—pushing through and assuming things will eventually level out.

Then my heart rate variability (HRV) dropped to 14.

That’s not just “a rough stretch.” That’s a real-time signal that my autonomic nervous system, the balance between sympathetic fight-or-flight and parasympathetic repair, is overwhelmed.

For shift workers, especially night nurses, that drop isn’t surprising. But it is actionable.

What HRV Is Really Telling Night Shift Nurses

HRV is a window into how flexibly your nervous system can move between gas and brake:

• High HRV → adaptability, recovery, resilience

• Low HRV → chronic strain, impaired recovery, higher cardiometabolic risk

Working nights pushes physiology toward the margins:

• Circadian mismatch: Awake and alert at the biologic low point.

• Fragmented daytime sleep: Light, noise, and life erode deep sleep.

• Inflammatory load: Night work + illness increases allostatic strain.

An acute illness layered on top of this can collapse HRV—exactly what happened when mine dropped to 14.

What the Research Shows: Night Shift Nurses Lose Sleep-Period Recovery

This isn’t anecdotal. We have evidence.

Researchers studying ICU nurses used 36 hours of continuous ambulatory HRV monitoring to compare permanent night nurses (n=11) with permanent day nurses (n=7). Instead of just raw HRV, they evaluated a heart rate variability coherence ratio—a measure of how well the heart, breathing, and baroreflex synchronize, especially during sleep.

Key results:

• Day nurses showed a clear rise in HRV coherence during sleep—a healthy parasympathetic recovery pattern.

• Night nurses did not, even though:

  • Fatigue, sleep quality, and psychomotor vigilance scores weren’t significantly different.

  • Physiologically, they were struggling earlier than symptoms suggested.

The pattern indicates autonomic dysregulation during the sleep period in night workers. Their sleep—their primary recovery window—does not deliver the same restorative parasympathetic support that day workers naturally receive.

Why this matters

Researchers concluded that:

• HRV coherence may serve as a novel biomarker for impaired recovery in night shift workers.

• Interventions like resonant-frequency breathing and HRV biofeedback may improve autonomic balance, cognitive performance, and sleep.

For any night nurse watching their HRV fall into the teens after illness, this study gives clarity: Your physiology is showing the strain before your symptoms do.

How Night Shift Workers Can Raise HRV

You can't change the hours, but you can change how your body survives them.

1. Protect the Recovery Window

Recovery—not willpower—moves HRV upward.

• Full blackout

• Cold room

• 20–30 minutes of wind-down

• Consistent sleep times on off days

Imperfect sleep is still better than inconsistent sleep.

2. Use Breathing to Directly Influence HRV

You can train the same pathways measured in HRV coherence.

Try:

• 4–6 breaths per minute

• Slow inhale, longer exhale

• 5–10 minutes before sleep or after waking

This recalibrates vagal tone.

3. Exercise Strategically

When HRV is low, shift from intensity to consistency.

• 7–12 minutes of moderate activity

• Avoid intense workouts during night stretches

• Save harder sessions for off rotations

Support recovery; don’t compete with it.

4. Remove Known HRV Suppressors

At least during vulnerable weeks:

• Alcohol

• Heavy ultra-processed meals midway through the shift

• Late-shift caffeine

• Staying awake all day post-shift

Each suppresses HRV for 24–72 hours.

5. Respect Transition Days

The move from nights to days is a physiologic inflection point.

• Skip the “stay up all day” punishment method

• Use a 90-minute anchor nap

• Gradually ease into daytime rhythm

Your biology responds better to gradual recalibration.

Where an HRV of 14 Fits In

A post-illness HRV of 14 isn’t a personal failure.

It is:

• A biometric indicator of overload

• A pattern well-documented in night shift physiology

• A prompt to prioritize structured recovery and, if needed, clinical evaluation

Recovery is not the absence of work—it is the work that keeps you in the game.

References

Burch et al., 2019 — Environmental HealthBurch, J.B., Morandi, M.T., Culp, K.M., Wilson, J.L., Suarez, V., Nangle, B.E., Yang, J., & Larkin, K.T. (2019). Heart rate variability coherence: A novel measure for detecting sympathetic and parasympathetic imbalance among permanent night shift workers. Environmental Health, 18, 99. https://doi.org/10.1186/s12940-019-0528-7

Burch et al., 2019 — Applied Psychophysiology & BiofeedbackBurch, J. B., Alexander, M., Balte, P., Sofge, J., Winstead, J., Kothandaraman, V., & Ginsberg, J. P. (2019). Shift Work and Heart Rate Variability Coherence: Pilot Study Among Nurses. Applied Psychophysiology and Biofeedback, 44(1), 21–30. https://doi.org/10.1007/s10484-018-9419-z

About the Author

R.E. Hengsterman is a registered nurse, medical writer, and author of The Shift Worker’s Paradox, with over 30 years of experience in emergency and trauma medicine. His work blends physiologic expertise with lived clinical experience, emphasizing evidence-based strategies for shift worker health.

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This article follows NurseWhoWrites editorial guidelines emphasizing evidence-based practice, transparent sourcing, and real-world clinical experience.