Circadian syndrome, abbreviated CircS, is a cluster of conditions arising from disruption of circadian rhythms. The researchers analyzed whether this prespecified phenotype was associated with incident Parkinson’s disease during follow-up among people who had not received a Parkinson’s disease diagnosis at the start of the study. Their objectives were threefold: to assess the longitudinal association between CircS and Parkinson’s disease risk, to examine whether that association varied according to genetic susceptibility, and to determine whether CircS contained risk information beyond that captured by metabolic syndrome.

Associations were estimated using Cox proportional hazards regression, and the researchers reported hazard ratios with 95% confidence intervals. The principal result was an adjusted hazard ratio of 1.22 for participants with circadian syndrome compared with those without it, indicating a 22% higher estimated risk associated with the syndrome after the model accounted for sociodemographic, lifestyle and genetic factors. The confidence interval of 1.11–1.34 quantifies the uncertainty around that estimate. In the same adjusted analysis, metabolic syndrome showed no independent association with incident Parkinson’s disease.

The relationship between circadian-syndrome burden and Parkinson’s disease was not linear. Compared with participants without CircS, those with component scores of 5, 6 and 7 had adjusted hazard ratios of 1.51, 1.88 and 5.74, respectively. Their 95% confidence intervals were 1.21–1.88 for a score of 5, 1.36–2.61 for a score of 6 and 2.90–11.37 for a score of 7. A test of the dose-response relationship confirmed significant nonlinearity, with P for nonlinearity below 0.0001. The estimate for the highest score was therefore substantially larger than those for scores of 5 and 6, although its wide confidence interval also showed that the magnitude of the estimate was imprecise.

The study also detected an interaction between circadian syndrome and Parkinson’s disease polygenic risk score. CircS was associated with the greatest increase in Parkinson’s disease risk among participants in the low-genetic-risk group. These findings do not establish that circadian disruption causes Parkinson’s disease or that treating CircS would prevent it; as an observational cohort analysis, the study reports associations rather than causal effects. Nevertheless, the results suggest that the prespecified CircS phenotype may capture information about Parkinson’s disease risk beyond metabolic syndrome and that circadian health could become a focus for future prevention research.

Subject of Research: Association between circadian syndrome and incident Parkinson’s disease in a UK Biobank cohort

Article Title: Circadian syndrome and incident Parkinson’s disease: a population-based cohort study

Article References: Xu, X., Hou, C., Zhao, F., Lv, Y., Tan, X., & Chen, L. (2026). Circadian syndrome and incident Parkinson’s disease: a population-based cohort study. npj Parkinson's Disease. https://doi.org/10.1038/s41531-026-01545-y

Image Credits: AI Generated

DOI: 10.1038/s41531-026-01545-y

Keywords: circadian syndrome, Parkinson’s disease, UK Biobank, population cohort, incident Parkinson’s disease, polygenic risk, metabolic syndrome, circadian disruption, hazard ratio, Circadian, syndrome, incident

The problem the researchers set out to solve is one of fragmentation. Liver aging involves several distinct cellular processes that are usually measured in isolation: the ploidy of hepatocytes, meaning how many copies of the genome each liver cell carries; the frequency of binucleated cells, which carry two nuclei; the proliferative activity of the tissue; and the accumulation of senescent cells that have permanently exited the cell cycle. Each of these features tells part of the story, but none of them alone describes the overall regenerative phenotype of the organ. The team’s answer was to combine them into single numerical descriptors that can be tracked over time and compared across experimental groups.

The first of these measures is the Index of Regenerative Reserve, abbreviated IRR. It is defined as the proportion of binucleated hepatocytes divided by the mean hepatocyte ploidy. The logic behind this ratio reflects the biology of the liver. Binucleated hepatocytes are generally associated with a state in which cells have completed cell-cycle events without dividing, and their abundance has been linked to regenerative flexibility. Mean ploidy, meanwhile, rises as hepatocytes undergo repeated rounds of genome duplication without cell division, a process known as polyploidization that becomes more prominent with age and chronic injury. By placing the proportion of binucleated cells over the average ploidy, the index captures the balance between these two faces of hepatocyte cell-cycle adaptation in a single value.

The second measure, the Integrated Index of Regenerative Status, or IRS, builds on the first by adding two molecular markers as fractional terms. The formula is IRS equals IRR multiplied by the quantity one plus Ki-67, divided by the quantity one plus p21. Ki-67 is a well-established marker of active cell proliferation, so a higher value indicates that more hepatocytes are actively cycling. p21 is a cyclin-dependent kinase inhibitor that enforces cell-cycle arrest and is widely used as a marker of cellular senescence. By multiplying the regenerative reserve by a proliferation-weighted numerator and a senescence-weighted denominator, the IRS is designed to fall when proliferative activity wanes or senescent arrest rises, and to hold steady or increase when the tissue retains its capacity to renew.

To test how these indices behave, the researchers turned to a model of accelerated aging that is unusual among liver studies: chronic circadian disruption. Male Wistar rats were assigned to three lighting conditions. A control group experienced normal light-dark cycles. A second group was kept under constant illumination, a condition the authors describe as dark deprivation, abbreviated DD. A third group experienced the same constant illumination but received melatonin at a dose of 10 milligrams per kilogram of body weight, five times weekly. Animals in all groups were assessed at four time points: 6, 12, 18, and 24 months of age, spanning a substantial fraction of the rat lifespan.

The rationale for this design rests on a growing body of evidence that light at night and disrupted circadian rhythms do more than disturb sleep. Previous work has shown that circadian disruption induced by light-at-night exposure can accelerate aging and promote tumorigenesis in rats, and the circadian clock itself has been shown to regulate hepatic polyploidy through the Mkp1-Erk1/2 signaling pathway. Constant illumination effectively deprives animals of the darkness that signals the pineal gland to produce melatonin, a hormone with antioxidant properties and broad influence over circadian physiology. The third group, in which melatonin was replaced exogenously, allowed the team to ask whether restoring the hormone could protect the liver’s regenerative profile.

The results were striking. In the dark-deprived animals, the Index of Regenerative Reserve fell from 2.00 plus or minus 0.42 at 6 months to 0.386 plus or minus 0.19 at 24 months, a decline of roughly eighty percent over the course of the study. The corresponding Integrated Index of Regenerative Status at 24 months was 0.32 plus or minus 0.17. These numbers depict a liver whose regenerative reserve is progressively eroded under conditions of chronic light exposure, consistent with the idea that circadian disruption drives pro-senescent remodeling of hepatic tissue.

In the animals that received melatonin alongside constant illumination, the picture was entirely different. At 24 months, the IRR in this group stood at 2.285 plus or minus 0.41 and the IRS at 2.08 plus or minus 0.16, values comparable to or even slightly above the starting levels seen in younger animals. In other words, exogenous melatonin appeared to preserve the composite regenerative profile of the liver across nearly the entire observation period, despite the animals being exposed to the same light regime as the unprotected group. The authors note that this finding aligns with their earlier work describing chronic light-induced desynchronosis as a model of accelerated metabolic aging in rats and the preventive role of melatonin in that context.

To explore whether the indices could discriminate between groups in a statistically meaningful way, the team performed an exploratory receiver-operating-characteristic analysis, a method borrowed from diagnostic testing that evaluates how well a continuous measure separates two conditions. The analysis yielded areas under the curve of 0.843 for the IRR and 0.905 for the IRS. An area under the curve of 1.0 represents perfect discrimination, while 0.5 represents chance performance, so values in the mid-0.8 to low-0.9 range indicate substantial, though not perfect, separation between the aging profiles of the dark-deprived and melatonin-treated animals. The IRS, which integrates molecular information on top of the structural measures, showed the stronger discriminatory performance.

The authors are careful about what these numbers do and do not establish. They present the IRR and IRS as experimental composite descriptors of the hepatic regenerative phenotype, and they state explicitly that external validation and direct functional regeneration assays are required before broader biological or clinical interpretation. The indices were developed and tested in a single animal model, and the receiver-operating-characteristic analysis was exploratory rather than confirmatory. Still, the approach addresses a real gap. Human studies have shown that hepatocyte expression of the senescence marker p21 is linked to fibrosis and adverse liver-related outcomes in alcohol-related liver disease, and that early liver regeneration after hepatectomy varies with age, yet clinicians lack integrated quantitative tools to gauge regenerative potential. If validated in independent models and eventually in human tissue, composite indices of this kind could offer a way to monitor how aging, circadian disruption, and interventions such as melatonin reshape the liver’s capacity to renew itself, turning a collection of scattered cellular measurements into a single readable signal of regenerative health.

Subject of Research: Quantitative composite indices of liver regenerative potential in a rat model of accelerated aging under circadian disruption and melatonin treatment

Article Title: Quantitative assessment of liver regenerative potential during accelerated aging: regenerative reserve and regenerative status indices

Article References: Areshidze, D. A., Kozlova, M. A., Anurkina, A. I., & Moskalev, A. (2026). Quantitative assessment of liver regenerative potential during accelerated aging: regenerative reserve and regenerative status indices. Biogerontology, 27(6), Article 179. https://doi.org/10.1007/s10522-026-10527-9

Image Credits: AI Generated

DOI: 10.1007/s10522-026-10527-9

Keywords: liver aging, hepatocyte polyploidy, binucleated hepatocytes, cellular senescence, melatonin, circadian disruption, regenerative capacity, Ki-67, p21, Biogerontology, Quantitative, assessment

The stakes are considerable. In industrialized societies, roughly 15 to 20 percent of the workforce labours outside the conventional daytime window of 6 a.m. to 6 p.m., staffing hospitals, mines, factories and transport networks through early mornings, evenings and nights. This pattern of work is consistently linked to elevated risks of cardiovascular disease, breast cancer and type 2 diabetes. The mechanisms appear to be multifactorial, involving circadian disruption, disturbed sleep, psychosocial stress and lifestyle behaviours, but one piece of the puzzle has remained frustratingly blurry: how much shift workers actually move and sit during their unpredictable days.

Traditional research tools struggle with this question. Self-report recall questionnaires ask people to summarize weeks or months of behaviour, an approach prone to memory errors and one that rarely accounts for the wild variation in shift schedules. A nurse finishing a night shift on Tuesday and starting an early shift on Thursday experiences fundamentally different days, and a single retrospective questionnaire flattens that complexity into a misleading average. EMA takes the opposite approach, pinging participants on their phones at scheduled moments and asking what they were doing in the preceding few minutes, capturing behaviour as it unfolds in its natural context.

In the study, the team recruited 128 workers in and around Brisbane, Ipswich and Toowoomba in south-east Queensland, ultimately analysing data from 120 participants, 58 percent of whom were female with a mean age of 36 years. The cohort included 69 shift workers, most of them nurses and paramedics, alongside 51 non-shift workers drawn from office settings. After downloading the SEMA3 smartphone app, participants were divided into three groups: shift workers receiving prompts tailored to their individual shift schedules, shift workers receiving standardized prompts, and non-shift workers receiving standardized prompts.

The prompting protocol was technically precise. Every participant received five surveys per day at three-hour intervals over seven to ten days, with the duration adjusted for shift workers so that data covered all their work patterns and days off. Tailored prompts were calculated from each worker’s anticipated shift schedule and wake-sleep pattern, then adjusted whenever the schedule changed. For night-shift workers, prompts ran from 10 p.m. to 10 a.m.; for evening shifts, from 1 p.m. to 1 a.m. Standardized prompts, by contrast, arrived between 10 a.m. and 10 p.m. regardless of schedule, deliberately avoiding hours when workers were likely asleep. Each survey contained five questions asking about current activity, its duration, its location, and any sitting involved, and took an average of just 24 seconds to complete. Unanswered surveys vanished after 30 minutes.

The recruitment results were strikingly strong. About 78 percent of invited workers enrolled, and every one of the 128 enrolled participants completed the study, with retention defined as responding to at least one prompt on four of seven days for non-shift workers and seven of ten days for shift workers. Those who declined mostly cited unwillingness to travel to the university for in-person meetings. Across the study, 4,482 prompts were sent, and 64 percent of surveys were started and completed, slightly below the 70 percent target the researchers set based on prior EMA literature, but comfortably within the wide 58 to 92 percent range reported in comparable studies.

The comparison between prompting strategies produced a nuanced picture. Shift workers on standardized prompts showed the lowest compliance at 57 percent, while tailored-prompt shift workers and non-shift workers reached 64 and 68 percent respectively, a difference that was not statistically significant. Interestingly, tailored-prompt shift workers answered more surveys on their days off than on working days, and were more likely to respond during day and evening shifts than during night shifts. Non-shift workers, meanwhile, responded more reliably on weekdays than weekends. The first prompt of the day attracted the highest response rate at 26 percent, while the fifth and final prompt drew only 14 percent, suggesting that engagement fades as the day wears on regardless of occupation.

Notably, compliance showed no relationship with age, gender, body mass index or marital status, an encouraging sign that EMA does not systematically exclude certain demographic groups. The researchers also found that reported activities differed across groups, with work duties the most frequently logged activity at 16.4 percent of responses, followed by phone or computer use, and non-shift workers reporting the highest levels of physical activity and television watching. Caring for children was the least reported activity at just one percent.

The authors are candid about why compliance fell short of the goal. Unlike some comparable workplace studies, their protocol sent no reminders and offered no monetary incentives, only personalized feedback on participants’ responses and movement. Evidence from meta-analyses suggests both reminders and incentives can lift completion rates, and an office-worker study that paid participants 20 dollars achieved higher compliance. The 30-minute expiry on unanswered prompts may also have cost responses. There are practical limits, too: workers in mining, manufacturing or retail may simply be unable to reach their phones during shifts, and the standardized 10 a.m. to 10 p.m. window may have missed early-morning and late-night behaviour entirely.

Even so, the study stands as one of the few to adapt EMA prompting to actual shift schedules, and its message is cautiously optimistic. Enrollment and retention were high, participant burden was demonstrably low, and the method generated thousands of within-person data points that traditional questionnaires could never capture. Beyond measurement, the researchers note that repeated real-time monitoring may itself make workers more aware of their habits, potentially prompting them to break up long stretches of sitting. If future studies can boost compliance through reminders, incentives and smarter tailoring, EMA could become the foundation for health promotion programs that know precisely when, and why, shift workers need support most.

Subject of Research: Feasibility of ecological momentary assessment for measuring physical activity and sedentary behaviour in shift and non-shift workers

Article Title: Feasibility of ecological momentary assessment in measuring physical activity and sedentary behaviour in shift and non-shift workers

Article References: Monnaatsie, M., Biddle, S. J., & Kolbe-Alexander, T. (2024). Feasibility of ecological momentary assessment in measuring physical activity and sedentary behaviour in shift and non-shift workers. Journal of Activity, Sedentary and Sleep Behaviors, 3(1), Article 24. https://doi.org/10.1186/s44167-024-00063-7

Image Credits: AI Generated

DOI: 10.1186/s44167-024-00063-7

Keywords: shift work, ecological momentary assessment, physical activity, sedentary behaviour, smartphone surveys, occupational health, EMA compliance, circadian disruption, nurses, mHealth, study feasibility, Feasibility

The study, published in BMC Endocrine Disorders by a team led by Kuoqing Zhang and Jianhui Wu of North China University of Science and Technology, draws on the Beijing-Tianjin-Hebei Health Effects Cohort. Between 2017 and 2018, the researchers enrolled 2,296 employees of a petroleum enterprise in Hebei Province, collecting detailed questionnaire data on work schedules and smoking history through trained interviewers, alongside baseline health examinations. From 2019 through 2025, the participants returned for annual follow-ups, allowing the team to track who developed new-onset hypertension-diabetes comorbidity over time. Because the study was prospective, meaning exposures were measured before disease appeared, it avoids much of the recall bias and reverse-causation ambiguity that weaken cross-sectional occupational studies.

To quantify shift exposure, the investigators calculated a Weighted Shift Index, a composite measure that captures not merely whether someone works shifts but how intense those schedules are, weighting factors such as the frequency of night rotations and the cumulative burden of circadian disruption. Smoking was similarly graded with a Smoking Index that reflects both intensity and duration of the habit. Rather than forcing these continuous measures into arbitrary cutoffs alone, the team also used restricted cubic splines, a flexible statistical technique that lets the data reveal the true shape of the dose-response relationship. That analysis proved revealing: the association between the Weighted Shift Index and comorbidity risk was non-linear, meaning risk did not climb in a straight line with increasing shift burden but followed a curved trajectory, with certain thresholds of exposure marking steeper rises.

Over the seven-year follow-up window, 8.6 percent of the cohort developed hypertension-diabetes comorbidity. That figure may sound modest, but in occupational health terms it represents a substantial burden of preventable cardiovascular and metabolic disease in a working population, many of whom are in the prime of their productive lives. When the researchers applied multivariate-adjusted modified Poisson regression, a method well suited to estimating relative risks in cohort data where outcomes are not rare, the picture sharpened considerably. Workers with high-intensity shift schedules faced a 69 percent higher risk of developing the comorbidity compared with their peers, with a relative risk of 1.693 and a confidence interval that excluded the null value with strong statistical confidence.

Smoking told an equally sobering story, and with an unexpected twist in the dose-response curve. Moderate smokers carried roughly double the risk of never-smokers, with a relative risk of 2.046, while heavy smokers were not far behind at 1.937. The fact that moderate smoking appeared slightly riskier than heavy smoking in this cohort is a curiosity the authors report transparently; it may reflect survivor effects, behavioral compensation, or chance variation within the confidence intervals, which overlap substantially between the two categories. What matters most is the consistent signal: both moderate and heavy smoking significantly elevated comorbidity risk, each with a p-value of 0.001, reinforcing the well-established vascular toxicity of tobacco smoke while adding a specific new outcome to its ledger.

The study’s most consequential finding, however, lies in the interaction analysis. Using the classic epidemiological framework of the relative excess risk due to interaction, the attributable proportion, and the synergy index, the team tested whether shift work and smoking act on the same disease pathway in a way that multiplies harm. For high-intensity shift work combined with heavy smoking, the attributable proportion reached 0.573, with a confidence interval of 0.025 to 1.121. In practical terms, this suggests that more than half of the comorbidity risk observed in this doubly exposed group could be attributed to the interaction itself, the part of the risk that exists only because the two exposures co-occur. It is the statistical signature of a genuine synergistic effect, the kind of biological amplification that occupational health guidelines rarely account for.

What biological mechanisms could underlie such synergy? The authors and the broader literature point to overlapping pathways of metabolic and vascular injury. Shift work disrupts the circadian regulation of cortisol, melatonin, blood pressure dipping during sleep and glucose homeostasis, promoting insulin resistance, sympathetic overactivation and chronic low-grade inflammation. Smoking, meanwhile, delivers nicotine and combustion products that impair endothelial function, increase oxidative stress and worsen insulin sensitivity. When a circadian-disrupted metabolism meets a chemically stressed vasculature, the combined insult may exceed the sum of its parts, accelerating the convergence of hypertension and type 2 diabetes into a single comorbid state. Intriguingly, the study also found that moderate-intensity shift work showed a certain protective effect, hinting that the relationship between schedule disruption and metabolic health may be more nuanced than a simple more-is-worse model, though the authors urge caution in over-interpreting that single result.

The choice of study population is not incidental. Petroleum workers represent a large, globally distributed workforce exposed to a distinctive cluster of occupational hazards: irregular schedules dictated by continuous operations, physically demanding tasks, psychological stress, and in many regions, high smoking prevalence shaped by workplace culture. Hypertension-diabetes comorbidity is particularly insidious in this context because each condition worsens the other; elevated blood pressure accelerates the vascular complications of diabetes, while hyperglycemia damages the kidneys and vessels that regulate blood pressure. Workers who develop the pairing face compounded risks of atherosclerotic cardiovascular disease, stroke, chronic kidney disease and retinopathy, often at ages well before such diseases typically strike.

For employers and regulators, the findings translate into a concrete intervention logic. Because the synergy between heavy smoking and high-intensity shift work accounts for a large share of the excess risk in the most vulnerable group, reducing either exposure should yield outsized benefits for that population. Workplace smoking cessation programs, circadian-aware rostering that limits the intensity and frequency of night rotations, and routine screening for blood pressure and fasting glucose among shift workers emerge as evidence-backed priorities. The study was funded by China’s National Key Research and Development Program and approved by the ethics committee of North China University of Science and Technology, with all participants providing written informed consent, underscoring the rigor behind the data.

As night-shift economies expand worldwide, from energy extraction to logistics to healthcare, this study adds a compelling data point to a growing scientific consensus: the timing of work is not a neutral variable in human health. When circadian disruption and chemical exposures such as tobacco collide in the same body, the resulting disease risk can be far greater than occupational safety frameworks currently assume. For the petroleum workers of Hebei Province, and for shift workers everywhere who smoke, the message from this seven-year cohort is unambiguous. The combination is not merely additive. It is a multiplier, and it is modifiable.

Subject of Research: Effects of shift work and smoking on new-onset hypertension-diabetes comorbidity in Chinese petroleum workers

Article Title: Association of shift work and smoking with new-onset hypertension-diabetes comorbidity in Chinese petroleum workers: a prospective cohort study

Article References: Zhang, K., Zhang, H., Liu, L., Wang, D., Zhang, M., Ma, X., Li, X., Xue, L., Wang, G., Yu, M., & Wu, J. (2026). Association of shift work and smoking with new-onset hypertension-diabetes comorbidity in Chinese petroleum workers: a prospective cohort study. BMC Endocrine Disorders. https://doi.org/10.1186/s12902-026-02570-x

Image Credits: AI Generated

DOI: 10.1186/s12902-026-02570-x

Keywords: hypertension-diabetes comorbidity, shift work, smoking, petroleum workers, prospective cohort study, occupational health, circadian disruption, cardiovascular risk, type 2 diabetes, interaction effect, relative risk, China