Daylight enhances the immune system’s ability to fight infections

A groundbreaking study by researchers from the University of Auckland in New Zealand, published in Science Immunology, has revealed that exposure to daylight can significantly enhance the immune system’s effectiveness in combating infections.

The research focused on neutrophils, the most abundant type of white blood cells in the human body and a critical part of the body’s first line of defense. These cells are the immune system’s rapid responders, rushing to infection sites to neutralize harmful pathogens.

Using danio fish (zebrafish) as a biological model, the scientists observed that immune responses were strongest in the morning, suggesting a link between immune activity and natural light cycles. This pattern is thought to be an evolutionary adaptation, corresponding with increased exposure to environmental pathogens during the day due to higher activity levels.

The study also found that neutrophils follow a circadian rhythm, making them more efficient in killing bacteria and fungi when exposed to daylight. These rhythms are regulated by internal biological clocks present in most cells, which synchronize with environmental cues like light and dark.

“This discovery opens exciting possibilities for developing therapies that align with or enhance the circadian rhythm of neutrophils,” said Associate Professor Christopher Hall, the study’s lead author. He added that light-based regulation of immune function may help improve treatments for infections, especially in patients with weakened immune systems.

The findings underscore the growing body of evidence linking circadian biology with immune function, and they pave the way for new strategies in immunotherapy that consider the timing and environmental context of treatment.