Natural killer (NK) cells play a critical role in protecting the body from illness. They act quickly to eliminate invading pathogens, foreign substances, and infected cells before these threats can spread. Some NK cells travel through the bloodstream (circulatory), while others remain in tissues and organs. When NK cell levels are too low, the immune system may not function properly, increasing vulnerability to disease.
Anxiety, Insomnia, and Immune Function
Anxiety disorder and insomnia are both known to interfere with normal immune activity. As these conditions become more common, researchers in Saudi Arabia set out to explore how anxiety and sleep problems might be linked to changes in NK cells among young female students. Their findings were published in Frontiers in Immunology.
“We found that in students with insomnia symptoms, count and percentage of total NK cells and their sub-populations were declined,” said first author Dr Renad Alhamawi, an assistant professor of immunology and immunotherapy at Taibah University. “Students with general anxiety symptoms, on the other hand, had a lower percentage and number of circulatory NK cells and their sub-populations, compared to symptom-free students.”
Who Took Part in the Study
A total of 60 female students aged 17-23 participated in the study. Each student completed three questionnaires covering sociodemographic information along with symptoms related to anxiety and insomnia. Reports of anxiety and sleep problems were self-reported. Survey results showed that about 53 percent of participants experienced sleep disturbances consistent with insomnia, while 75 percent reported anxiety symptoms. Roughly 17 percent and 13 percent fell into the moderate and severe anxiety categories.
Blood samples were also collected to measure NK cell levels and identify specific subtypes. NK cells fall into two main categories. CD16+CD56dim cells make up most NK cells in the nervous system that connects the central nervous system to the rest of the body (peripheral NK cells). These cells are cytotoxic, meaning they can damage or kill cells that pose a threat. The second group, CD16+CD56high cells, appears less often and is involved in producing proteins that act as chemical messengers and help regulate immune responses. Both groups are classified as circulatory NK cells.
Anxiety Severity and NK Cell Declines
The analysis showed that students reporting anxiety symptoms had both lower percentages and lower numbers of circulatory NK cells and their sub-populations compared to students without symptoms. The extent of anxiety mattered. Those with moderate or severe anxiety showed a clearly reduced percentage of circulatory NK cells, while students with minimal or mild anxiety showed only a small decline that was not statistically significant. Among students with insomnia symptoms, higher anxiety scores were linked to lower proportions of total peripheral NK cells.
How Stress May Undermine Immunity
Reduced NK cell levels can weaken immune defenses and may increase the risk of illness, cancer, and mental health conditions, including depression. “Understanding how these psychological stressors influence the distribution and activity of immune cells, especially peripheral NK cells, may provide valuable insights into the mechanisms underlying inflammation and tumorigenesis,” Alhamawi explained.
Study Limits and Future Research
The research team noted several limitations. The study focused only on young females, a group in which anxiety and sleep disorders have been rising at a disproportionate rate. This narrow sample limits how broadly the findings can be applied. The researchers emphasized that future studies should include people of different ages, sexes, and geographic backgrounds to better understand how anxiety and insomnia affect NK cell levels and function.
Lifestyle Factors and Long-Term Health
Previous research suggests that healthy habits, such as regular physical activity, stress management, and a balanced diet, can support NK cell numbers and performance. Even so, anxiety and insomnia can disrupt multiple systems in the body, including the immune system, and may contribute to chronic and inflammatory diseases.
“Such impacts ultimately compromise overall health and quality of life,” concluded Alhamawi.
Reference: “Insomnia and anxiety: exploring their hidden effect on natural killer cells among young female adults” by Renad M. Alhamawi, Fatmah A. Halawani, Sima F. Hakeem, Hadeel A. Alslimi, Ebraheim M. Alhamawi, Ahmed M. Aljohani, Ibrahim N. Mohammed, Heba M. Zahid and Yahya A. Almutawif, 9 October 2025, Frontiers in Immunology.
DOI: 10.3389/fimmu.2025.1698155
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