Tag: chronobiology

Association between light exposure patterns and multidimensional health outcomes in individuals with myalgic encephalomyelitis/chronic fatigue syndrome: findings from an observational cross-sectional cohort study

Abstract:

Background: Light is a major environmental factor regulating circadian rhythms, sleep- wake cycles, and mood-related behaviors. Patients with Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) often experience circadian disruption and poor sleep quality, which severely compromise their quality of life; however, the relationship between light exposure and illness severity remains largely unknown.

Methods: An observational cross-sectional cohort secondary study used collected data from 100 ME/CFS patients and 56 healthy controls to explore the impact of spontaneous light exposure on multidimensional health status and circulating biochemical parameters. Demographic and clinical features were assessed using validated patient-reported outcome measures. Light intensity, wrist temperature, and physical activity were continuously monitored at home over one week using wrist-worn actigraphy. Light intensity during predefined intervals and rhythmic variables of light cycle were calculated. Principal component analysis (PCA) was applied to reduce dimensionality of light variables. Multivariable analysis was performed adjusting for age, sex, body mass index, and physical activity.

Results: Following PCA of the light patterns, two components emerged across groups with high consistency: PC1 (explaining 61.7% of the total variance) reflected higher daytime light and rhythm stability, and PC2 (explaining 16.1%) represented nocturnal/early-morning light and rhythm instability. In ME/CFS patients, light variables were more extensively associated with clinical outcomes measures (FIS-40, PSQI and SF-36) than in healthy controls (all p < 0.05). Furthermore, PC2 was associated with higher levels of VCAM-1 and triglycerides, and lower serotonin concentrations (all p < 0.05). Four distinct light patterns were identified based on PCA scores: nocturnal light, healthy, adverse, and low diurnal light. ME/CFS patients exhibiting the healthy light pattern showed significantly lower fatigue, fewer sleep complaints, reduced autonomic dysfunction, and higher quality of life compared to those with the adverse light pattern (all p < 0.05). No significant differences were observed among healthy controls.

Conclusions: Light exposure patterns show distinct associations with symptom variability in ME/CFS compared to healthy controls. More stable daytime light appears to relate to better symptom profiles, whereas irregular exposure and nocturnal light are linked to poorer health outcomes. Although causality cannot be inferred, these findings highlight light exposure as a potentially modifiable, non-invasive target for behavioral interventions aimed at improving the quality of life in ME/CFS, representing a promising emerging for future translational research.

Source: Cambras T, Domingo JC, Sanmartín-Sentañes R, Alegre-Martín J, Castro-Marrero J. Association between light exposure patterns and multidimensional health outcomes in individuals with myalgic encephalomyelitis/chronic fatigue syndrome: findings from an observational cross-sectional cohort study. J Transl Med. 2026 Jul 3. doi: 10.1186/s12967-026-08556-6. Epub ahead of print. PMID: 42399727. https://link.springer.com/article/10.1186/s12967-026-08556-6 (Full text available as PDF file)

Systems neuroendocrinology in ME/CFS and long COVID: a chronobiological framework for hormone-based research

Abstract:

Hormonal dysregulation is increasingly reported in ME/CFS and Long COVID, yet the broader role of neuroendocrine disruption in these conditions remains underexplored. While changes in steroid, peptide, and neuropeptide hormones have been identified, these findings are often considered in isolation and without attention to their timing or integration within broader physiological systems. The hypothalamic-pituitary axes regulate endocrine, immune, autonomic, nervous, and metabolic functions, systems commonly affected in both conditions, yet their circadian and menstrual dynamics are rarely investigated.

In this review, we examine the evidence for neuroendocrine dysfunction in ME/CFS and Long COVID, focusing on hormone output, functional assays, receptor expression, and the coordination of endocrine biorhythms. Sex hormone signalling emerges as a key area of vulnerability, particularly given the female predominance in both conditions and the complexity of reproductive hormone regulation.

We argue that accurate hormone measurement and time-structured sampling, including circadian and menstrual rhythms, are essential for detecting meaningful biological differences. By embedding chronobiology-aware, dense-sampling strategies and integrating multi-omic analyses into multi-system study designs, we outline a framework for investigating dynamic endocrine mechanisms underlying symptom variability and multisystem dysfunction, which may ultimately support the development of more targeted, personalised interventions.

Source: Thomas N, Huang K, Schneider-Futschik EK, Pollack B, Tal MC, Fineberg D, Wang X, Gurvich C, Pretorius R, Bergquist J, Armstrong CW. Systems neuroendocrinology in ME/CFS and long COVID: a chronobiological framework for hormone-based research. Front Neuroendocrinol. 2026 Jun 19:101268. doi: 10.1016/j.yfrne.2026.101268. Epub ahead of print. PMID: 42320559. https://www.sciencedirect.com/science/article/abs/pii/S0091302226000385 (Full text)

Circadian rhythm abnormalities and autonomic dysfunction in patients with Chronic Fatigue Syndrome/Myalgic Encephalomyelitis

Abstract:

Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (CFS/ME) patients frequently show autonomic symptoms which may be associated with a hypothalamic dysfunction. This study aimed to explore circadian rhythm patterns in rest and activity and distal skin temperature (DST) and their association with self-reported outcome measures, in CFS/ME patients and healthy controls at two different times of year.

Ten women who met both the 1994 CDC/Fukuda definition and 2003 Canadian criteria for CFS/ME were included in the study, along with ten healthy controls matched for age, sex and body mass index. Self-reported measures were used to assess fatigue, sleep quality, anxiety and depression, autonomic function and health-related quality of life. The ActTrust actigraph was used to record activity, DST and light intensity, with data intervals of one minute over seven consecutive days. Sleep variables were obtained through actigraphic analysis and from subjective sleep diary. The circadian variables and the spectral analysis of the rhythms were calculated. Linear regression analysis was used to evaluate the relationship between the rhythmic variables and clinical features. Recordings were taken in the same subjects in winter and summer.

Results showed no differences in rhythm stability, sleep latency or number of awakenings between groups as measured with the actigraph. However, daily activity, the relative amplitude and the stability of the activity rhythm were lower in CFS/ME patients than in controls. DST was sensitive to environmental temperature and showed lower nocturnal values in CFS/ME patients than controls only in winter. A spectral analysis showed no differences in phase or amplitude of the 24h rhythm, but the power of the second harmonic (12h), revealed differences between groups (controls showed a post-lunch dip in activity and peak in DST, while CFS/ME patients did not) and correlated with clinical features. These findings suggest that circadian regulation and skin vasodilator responses may play a role in CFS/ME.

Source: Cambras T, Castro-Marrero J, Zaragoza MC, Díez-Noguera A, Alegre J. Circadian rhythm abnormalities and autonomic dysfunction in patients with Chronic Fatigue Syndrome/Myalgic Encephalomyelitis. PLoS One. 2018 Jun 6;13(6):e0198106. doi: 10.1371/journal.pone.0198106. eCollection 2018.  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5991397/  (Full article)