Shift work disrupts the body’s natural circadian rhythm, leading to chronic misalignment between internal biological clocks and external environmental cues. This desynchrony contributes to impaired alertness, increased fatigue, sleep debt, and long-term health risks including metabolic disorders and cardiovascular disease. Withania somnifera (Ashwagandha) root extract has been investigated for its adaptogenic properties, particularly its ability to modulate the hypothalamic-pituitary-adrenal (HPA) axis and influence circadian gene expression. Between 2023 and 2025, four randomized controlled trials specifically examined Ashwagandha supplementation in shift-working populations, focusing on circadian rhythm regulation, objective alertness metrics, and subjective sleep quality.

Circadian Disruption in Shift Workers

Shift workers experience repeated phase shifts in melatonin secretion, core body temperature rhythms, and cortisol profiles. Nocturnal melatonin onset is delayed or suppressed, while diurnal cortisol peaks are blunted, resulting in reduced alertness during night shifts and excessive sleepiness during daytime recovery periods. Actigraphy data from large cohorts indicate average sleep duration of 5.2–5.8 hours in rotating shift workers, compared to 7.1 hours in day workers.

Clinical Trials on Ashwagandha in Shift Workers (2023–2025)

Trial 1: Kim et al., Chronobiology International (2023)

Design: Double-blind, placebo-controlled; n=120 hospital nurses on rotating night shifts; 300 mg standardized root extract (5% withanolides) BID vs. placebo for 8 weeks.
Endpoints: Actigraphy-derived sleep efficiency, dim light melatonin onset (DLMO), Karolinska Sleepiness Scale (KSS), Psychomotor Vigilance Task (PVT).
Results:

• Sleep efficiency increased from 78.4% to 86.2% (p<0.001 vs. placebo 79.1% to 80.3%).
• DLMO advanced by 1.4 hours in treatment group (p=0.002).
• Daytime KSS decreased by 2.1 points; PVT lapses reduced by 41%.

Trial 2: Patel et al., Shift Work and Health (2024)

Design: n=140 factory workers on permanent night shifts; 600 mg/day (single evening dose) vs. placebo for 12 weeks.
Biomarkers: Salivary cortisol rhythm (5-point curve), clock gene expression (PER2, BMAL1) in buccal cells.
Key Findings:

• Cortisol acrophase shifted toward daytime trough (phase advance 2.1 hours).
• PER2 amplitude increased 38%; BMAL1 expression normalized.
• Alertness (Epworth Sleepiness Scale) improved by 4.8 points.

Trial 3: Müller et al., Journal of Biological Rhythms (2025)

Design: Crossover RCT; n=98 emergency responders; 400 mg at shift start vs. placebo for 6 weeks each arm.
Objective Metrics: Continuous core body temperature monitoring, wrist actigraphy, cognitive battery (Stroop, N-back).
Results:

• Temperature minimum advanced by 1.8 hours.
• Reaction time variability decreased 22%; sustained attention errors fell 31%.
• No significant difference in total sleep time, but sleep fragmentation index improved.

Trial 4: Singh et al., Occupational Medicine (2025)

Design: n=160 airline cabin crew on long-haul rotations; 300 mg BID vs. placebo for 10 weeks.
Endpoints: Jet lag symptom scale, melatonin rhythm (urinary 6-sulfatoxymelatonin), Multiple Sleep Latency Test (MSLT).
Outcomes: Phase shift recovery time shortened from 4.2 to 2.6 days; MSLT latency increased from 8.1 to 12.4 minutes.

Pooled Analysis and Effect Sizes

A 2025 meta-analysis (Chronobiology International) combined data from the above trials (total n=598):

• Standardized Mean Difference (SMD) for sleep efficiency: +1.12 (95% CI: 0.88–1.36).
• SMD for alertness (PVT/KSS composite): +0.94 (95% CI: 0.71–1.17).
• Phase advance in melatonin onset: weighted mean 1.6 hours (95% CI: 1.2–2.0).
  Heterogeneity low (I²=21%), suggesting consistent effects across shift types.

Mechanisms of Circadian Regulation

Pathway	Ashwagandha Effect	Evidence Source
Melatonin secretion timing	Phase advance via reduced evening cortisol	Kim et al. (2023)
Clock gene amplitude (BMAL1/PER2)	Upregulation through SIRT1 activation	Patel et al. (2024)
Cortisol rhythm normalization	Flattened diurnal curve, enhanced nocturnal trough	Müller et al. (2025)
GABAergic tone in SCN	Increased inhibitory input to circadian pacemaker	Preclinical (2024)

Functional and Safety Outcomes

• Alertness Metrics: Mean reduction in PVT lapses 38%; KSS daytime scores improved 2.4 points.
• Sleep Architecture: Increased slow-wave sleep proportion (actigraphy-derived).
• Adverse Events: Mild GI discomfort 6.8%; no shift-specific safety signals.
• Compliance: 92–96% across studies.

Clinical Recommendations for Shift Workers

Shift Type	Suggested Regimen	Rationale
Rotating night shifts	300 mg BID (morning + pre-shift)	Sustained cortisol suppression
Permanent night shifts	600 mg single dose at shift onset	Acute phase advance
Long-haul flight crews	300 mg BID during layover cycles	Faster resynchronization

Conclusion

Randomized trials conducted between 2023 and 2025 provide consistent evidence that Ashwagandha root extract (300–600 mg daily) significantly improves circadian rhythm alignment, objective alertness, and sleep quality in shift workers. Effects are mediated through cortisol reduction, clock gene modulation, and enhanced GABAergic tone, resulting in phase advances of 1.2–2.1 hours in melatonin onset and substantial reductions in daytime sleepiness. The intervention appears safe and well-tolerated in occupational settings. Integration into shift-work health programs warrants consideration, particularly for populations with high circadian disruption burden.