A large, case-control study from Sweden finds that people with long COVID have higher rates of depression, anxiety, fatigue, and headache both before and after diagnosis. The findings, published last week in BMC Medicine, draw on medical records from more than 53,000 adults and suggest a link between long COVID and preexisting conditions.
Across the three time periods examined—in 2019, in the year leading up to diagnosis, and in the six months afterward—people diagnosed with long COVID consistently had higher rates of depression, anxiety, headache, and fatigue-related conditions than those in the control group, with a higher frequency of all studied diagnoses in the year before and six months after a long COVID diagnosis. Fatigue-related diagnoses and headache had the most significant association with long COVID.
While the risks of fatigue syndrome after a COVID infection in women and for headache in men declined slightly in the six months after diagnosis compared with the year before, they remained above pre-pandemic levels. (Two-thirds of participants were women.)
It’s estimated that around 10% to 30% of people with a previous COVID diagnosis are affected by long COVID, with some longitudinal studies reporting rates as high as 46%.
Symptom burden before diagnosis doesn’t imply causation
The study authors emphasize that higher rates of depression, anxiety, headache, and fatigue before COVID infection don’t imply that they cause post-COVID symptoms. Instead, they propose that shared biological pathways such as chronic inflammation, neuroinflammation, autonomic dysfunction, and immune responses, may explain the association between pre- and post-diagnosis symptom burden. Psychosocial factors may also play a role.
The study’s strengths include its large, population-based design and matching cases and controls by age, sex, and socioeconomics (to reduce confounding bias). Limitations include potential surveillance bias (patients with prior mental health diagnoses may seek care more often) and difficulty distinguishing new-onset symptoms from preexisting conditions.
“Our results support the hypothesis that individuals who develop long COVID may represent a distinct clinical phenotype characterized by an increased burden of mental health-related symptoms, both before and after infection with SARS-CoV-2” the authors conclude.
