García-Borreguero, D, Dale, J K, Rosenthal, N E et al. · Psychiatry research · 1998 · DOI
Many people experience changes in energy, mood, appetite, and sleep across different seasons, often feeling worse in winter. This study tested whether ME/CFS patients experience these same seasonal changes. The researchers found that ME/CFS patients actually show much less seasonal variation in their symptoms compared to healthy people, suggesting their fatigue and other symptoms stay relatively constant year-round rather than fluctuating with the seasons.
This finding is clinically significant because it suggests ME/CFS has a fundamentally different physiological basis than seasonal mood disorders, which may inform treatment approaches. Understanding that ME/CFS symptoms remain stable across seasons helps clinicians and patients recognize that symptom fluctuations may be driven by factors other than environmental seasonality, such as disease-specific mechanisms or activity patterns.
This study does not prove that seasonal factors never influence individual ME/CFS patients—there may be patient subgroups with seasonal sensitivity not detected in group-level analysis. It also does not establish why ME/CFS patients lack seasonal variation; the underlying biological mechanism remains unclear. The cross-sectional design cannot determine causation or whether this reduced seasonal sensitivity is a primary feature of ME/CFS or a secondary consequence of the illness.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
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