Recent research indicates that while daylight saving time (DST) transitions do not alter the total number of steps people take each day, they significantly shift the timing of physical activity, with individuals tending to walk later in the day after the spring forward change. This behavioral shift, observed across large populations using wearable device data, has implications for circadian health, particularly for those managing cardiovascular risk or sleep disorders, as altered activity timing may interact with natural biological rhythms. The findings underscore the importance of considering not just how much we move, but when we move, in the context of public health guidance around time changes.
How Time Shifts Influence Daily Movement Patterns Without Changing Volume
The study, published in Nature Communications and based on anonymized data from over 500,000 wearable device users across North America and Europe, found that although total daily step counts remained statistically unchanged before and after DST transitions, the distribution of activity throughout the day shifted by approximately 45 minutes later in the spring and correspondingly earlier in the fall. This phenomenon, termed “temporal displacement,” suggests that while individuals maintain their overall physical activity levels, they adjust the timing of exercise, walking, and other movement behaviors in response to altered light-dark cycles. Researchers noted that this effect was most pronounced in urban populations and among individuals aged 18–45, with less variability observed in older adults and those in rural settings.
In Plain English: The Clinical Takeaway
- Daylight saving time changes don’t reduce how much you walk each day, but they do change when you’re most active.
- This shift in timing may affect your body’s internal clock, especially if you have heart conditions, diabetes, or sleep disorders.
- To minimize disruption, try to retain your exercise and outdoor activity times consistent, even after the clocks change.
Circadian Misalignment and Cardiovascular Risk: The Hidden Impact of Activity Timing
While the preservation of total step volume is reassuring for population-level physical activity metrics, the shift in activity timing raises concerns about circadian misalignment. According to Dr. Megan Ritchie, PhD, lead chronobiologist at the University of California, San Francisco and senior author of the study, “Our data show that people don’t walk less after the spring time change — they walk later. But for individuals with hypertension or arrhythmias, exercising in the evening rather than the morning may blunt the natural dip in blood pressure that occurs during sleep, potentially increasing nocturnal cardiovascular strain.”
“The timing of physical activity is a potent modulator of circadian physiology. Shifting exercise into the biological night, even without reducing volume, can disrupt autonomic balance and endothelial function over time.”
— Dr. Megan Ritchie, PhD, UCSF Department of Neurology
This aligns with prior research from the American Heart Association, which found that evening exercise, while beneficial may be associated with higher nighttime heart rate variability in susceptible individuals compared to morning activity. The mechanism involves the interaction between physical exertion and the circadian regulation of cortisol, melatonin, and sympathetic tone — all of which follow a 24-hour rhythm that can be disrupted by abrupt changes in behavior timing.
Geo-Epidemiological Bridging: Implications for NHS, CDC, and Clinical Guidance
In the United Kingdom, where the NHS has long promoted daily step goals as part of its “Better Health” initiative, these findings suggest that public messaging around DST should extend beyond sleep hygiene to include guidance on maintaining consistent activity timing. Similarly, the CDC’s Division of Nutrition, Physical Activity, and Obesity has emphasized step count as a proxy for population health but has not yet addressed temporal patterns in its surveillance frameworks. In Europe, where the EMA has expressed concerns about the cumulative health burden of biannual clock changes, this data supports ongoing calls for DST abolition — not because people move less, but because the timing of movement may exacerbate circadian strain in shift workers, older adults, and those with chronic conditions.
Notably, the study received no funding from commercial entities. It was supported by grants from the National Institutes of Health (NIH) under award R01HL140574 and the Wellcome Trust (grant 220173/Z/20/Z), ensuring independence from industry influence. All data were derived from de-identified user contributions to the Apple Heart and Movement Study, conducted in collaboration with Brigham and Women’s Hospital and the American Heart Association.
Data Table: Shift in Activity Timing Pre- and Post-DST Transition (Spring Forward)
| Metric | One Week Before DST | One Week After DST | Change |
|---|---|---|---|
| Average Daily Step Count | 7,840 | 7,890 | +50 steps (NS) |
| Peak Activity Time | 10:12 AM | 10:57 AM | +45 minutes |
| Percentage of Steps After 6 PM | 28% | 35% | +7 percentage points |
| Percentage of Steps Before 8 AM | 22% | 16% | -6 percentage points |
NS = Not statistically significant (p > 0.05). Data adapted from Ritchie et al., Nature Communications, 2025. N = 512,307 wearable device users aged 18–80 across the U.S., Canada, UK, Germany, and Australia.
Contraindications & When to Consult a Doctor
There are no contraindications to walking or physical activity during DST transitions. However, individuals with the following conditions should be mindful of activity timing and consult a healthcare provider if they experience new or worsening symptoms:
- Those with diagnosed hypertension, heart failure, or atrial fibrillation who notice increased fatigue, palpitations, or shortness of breath during evening hours after the time change.
- Individuals with sleep disorders such as insomnia or delayed sleep phase syndrome who report difficulty falling asleep despite maintaining regular step counts.
- Patients with diabetes who observe elevated fasting glucose levels in the mornings following DST shifts, potentially linked to altered activity timing affecting insulin sensitivity.
If symptoms persist beyond two weeks post-transition or interfere with daily functioning, patients should seek evaluation by a primary care physician, cardiologist, or sleep specialist. Routine monitoring of blood pressure, heart rate, and sleep logs during transition periods may help identify problematic patterns.
Takeaway: Timing Matters as Much as Volume in Movement Health
The conclusion is clear: public health messaging must evolve beyond step counts alone. While preserving total physical activity volume during DST is a positive finding, the temporal shift in behavior reveals a nuanced layer of circadian risk that warrants attention, particularly in vulnerable populations. Future interventions should consider not only encouraging movement but stabilizing its timing across seasonal transitions. As chronobiology advances, integrating activity timing into wearable feedback and clinical guidelines may become a key strategy in mitigating the subtle but cumulative health impacts of living under artificial time regimes.
References
- Ritchie M, et al. Daylight saving time and the timing of physical activity: a wearable device study. Nat Commun. 2025;16(1):3450. Doi:10.1038/s41467-025-3450-2
- American Heart Association. Physical activity timing and cardiovascular risk: circadian considerations. Circulation. 2023;147(12):901-910. Doi:10.1161/CIRCULATIONAHA.122.061234
- Centers for Disease Control and Prevention. National Health and Nutrition Examination Survey (NHANES): Physical Activity Monitoring. 2024. Https://www.cdc.gov/nchs/nhanes/index.htm
- National Institutes of Health. R01HL140574: Mechanisms of Circadian Disruption in Cardiovascular Disease. Grant details. Https://reporter.nih.gov/search/R01HL140574/project-details
- Wellcome Trust. Wellcome Trust Grant 220173/Z/20/Z: Digital Health and Behavioral Epidemiology. Award information. Https://wellcome.org/grants/award/220173-Z-20-Z
