Estonian study finds two-way link between long COVID and chronic illness
University of Tartu researchers analyzing data from over 200,000 Estonian Biobank participants found that chronic diseases prolong COVID-19 symptoms, while long COVID in turn raises the risk of new chronic conditions such as diabetes.
A new study by researchers at the University of Tartu shows that long COVID and chronic illness are linked in both directions — each can raise the risk of the other. The team analyzed health and genetic data from nearly 210,000 Estonian Biobank donors, comparing more than 2,000 people with long COVID to roughly 200,000 people in a control group.
Who is most at risk
Long COVID most often affected people aged 40–59, and three-quarters of those with prolonged symptoms were women. The risk was significantly raised by being overweight and by prior chronic kidney disease, asthma or type 2 diabetes. People with chronic obstructive pulmonary disease faced more than double the usual risk of persistent symptoms.
New diagnoses following COVID
During the pandemic, doctors diagnosed new health problems considerably more often in patients who had long COVID. The risk of sleep apnea, for instance, was three times higher than before, while heart rhythm disorders and thyroid disease also became more common. Researchers noted they cannot rule out that long COVID patients simply see doctors more often and are therefore diagnosed more.
Type 2 diabetes drew particular attention: starting in spring 2020, new diabetes cases in the general population rose sharply, exceeding earlier projections. People with a higher genetic predisposition to severe COVID developed diabetes 17 percent more often.
Researchers say the virus affects the body on multiple fronts — existing chronic conditions foster inflammation and immune disturbances that hinder full recovery, while the rise in diabetes cases may reflect the virus's impact on the insulin-producing pancreas. Pandemic-era lifestyle changes, including less physical activity, higher stress and weight gain, also contributed. The findings were published in the journal Frontiers in Public Health.
