Heart attacks rarely arrive with warning, but many patients notice a strange pattern: mornings often seem worse.
Doctors have long observed that heart attacks occurring early in the day tend to cause more extensive damage than those at night, even when treatment is similar.
Scientists have been searching for an explanation that goes beyond blood pressure and stress hormones. New research now points to the body’s own immune system as a critical factor.
Timing inside the body
According to a peer-reviewed study published in the Journal of Experimental Medicine, researchers at Yale University School of Medicine found that neutrophils, a type of immune cell, follow a daily rhythm that affects how aggressively they behave.
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During daytime hours, these cells are more active and more likely to damage healthy tissue while responding to injury.
Using mouse models of heart attack, the team showed that neutrophils contribute more strongly to heart muscle damage when an attack happens in the morning.
This helps explain why earlier cardiac events often lead to larger areas of injury and poorer recovery.
Switching to night mode
The researchers tested a drug called ATI2341 that interferes with the internal clock of neutrophils.
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By shifting the cells into a “night-like” state, the immune response became less destructive.
Neutrophils moved toward the center of damaged tissue instead of spreading along its edges, limiting harm to surrounding healthy heart muscle.
Importantly, the altered immune behavior did not weaken the body’s ability to fight bacterial or fungal infections, a common risk with immune-suppressing treatments.
Potential clinical impact
The findings suggest that targeting immune cell timing could become a new way to reduce heart damage after a cardiac event, without compromising overall immunity.
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While the work is still experimental and limited to animal studies, it opens a path toward treatments that fine-tune inflammation rather than shutting it down entirely.
Researchers say future studies will need to explore whether similar strategies are safe and effective in humans, and whether timing treatments to the body’s internal clock could improve recovery after heart attacks.
Sources: Eurekalert and Rupress
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