Depressive symptoms are common in people with asthma, but increasing evidence suggests they may be driven by biological processes that differ from those seen in major depressive disorder.
Researchers from Hiroshima University in Japan, working with collaborators, have identified a biological difference in how depression appears in adults with asthma.
Their study found that people with asthma who report depressive symptoms have higher levels of a protein called brain-derived neurotrophic factor, or BDNF, in their blood. This stands in contrast to major depressive disorder, where BDNF levels are typically lower.
The results, published in The Journal of Allergy and Clinical Immunology: In Practice, suggest that depression linked to asthma may arise through different biological pathways than primary depression.
Depressive symptoms in people with asthma are often associated with poorer disease control and greater severity. While low BDNF is a recognized feature of major depressive disorder, the protein also plays important roles outside the brain.
It is produced in the lungs as well, where levels increase during airway inflammation. In this setting, BDNF can influence nerve signaling and inflammatory responses, which may heighten airway sensitivity and worsen asthma symptoms. These overlapping roles raise the question of whether depression in asthma follows the same biological mechanisms seen in primary depression.
Asthma depression follows different biology
To investigate this further, the researchers examined 140 adults diagnosed with asthma. They measured blood concentrations of BDNF and evaluated symptoms of depression and anxiety. Participants also wore motion sensors that tracked their daily physical activity, allowing the team to explore connections between disease severity, movement levels, and mental health.
“Unlike major depressive disorder, patients with asthma who have depressive symptoms show higher, not lower, serum BDNF levels. Moreover, elevated BDNF is associated with greater asthma severity,” says study corresponding author Hiroshi Iwamoto, associate professor at Hiroshima University’s Graduate School of Biomedical and Health Sciences. “These results suggest that the biological mechanisms underlying depressive symptoms in asthma may be different from those in major depressive disorder.”
The study also found that individuals who were less physically active tended to report worse mood. This suggests that the physical limitations caused by asthma may contribute to emotional distress. The researchers propose that BDNF may serve as an indicator of physiological strain or inflammation in the body, which could help explain why depression in asthma does not follow the same biological pattern as major depressive disorder.
Physical activity linked to mood
The findings further emphasize the role of daily activity. Even after taking asthma severity into account, participants with lower levels of physical activity experienced more depressive symptoms.
“The next step is to clarify the causal pathways linking asthma severity, BDNF and depressive symptoms through longitudinal and interventional studies,” adds Iwamoto. Addressing asthma and mental health together, rather than separately, may provide the greatest benefit for patients.
Reference: “Brain-Derived Neurotrophic Factor Levels Are Associated With Depressive Symptoms in Patients With Asthma” by Kazuma Kawamoto, Hiroshi Iwamoto, Tsunahiko Hirano, Akihito Yokoyama, Kazuto Matsunaga, Noboru Hattori, 10 November 2025, The Journal of Allergy and Clinical Immunology: In Practice.
DOI: 10.1016/j.jaip.2025.11.001
This work was partially supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
The open access publication costs for this paper were supported by Hiroshima University.
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