A New Study Links Stress & Sleep Issues With Lower Levels Of Key Immune Cells
For years, “stress makes you sick” was thought of more as a wellness cliché than a biological fact. But a growing body of research suggests there’s real truth behind the phrase. Chronic stress doesn’t just affect how you feel emotionally; it can alter immune function at the cellular level, changing how well your body defends itself against illness.
A study published in Frontiers in Immunology found that anxiety and insomnia were both associated with significantly lower levels of natural killer (NK) cells, one of the immune system’s first lines of defense. And the more severe the anxiety, the steeper the drop.
In other words: chronic stress doesn’t just feel bad. It may actively thin the immune army meant to protect you.
But first: What are killer cells and what role do they play in the immune system?
Natural killer cells are part of the innate immune system, your body’s rapid-response team. They patrol the bloodstream and tissues, identifying and destroying infected, damaged, or abnormal cells before problems can escalate.
There are two key subtypes:
- CD16+CD56dim cells, which make up the majority of circulating NK cells and are highly cytotoxic, meaning they directly destroy harmful cells
- CD16+CD56high cells, which help regulate immune signaling and inflammation
When NK cell numbers drop too low, the immune system may struggle to contain infections or abnormal cell growth early on—raising long-term health risks.
Study shows that stress, anxiety, & sleep issues lower NK cells
Researchers examined 60 female university students between the ages of 17 and 23. The participants completed validated questionnaires assessing self-reported anxiety and insomnia symptoms, then provided blood samples so researchers could measure different NK cell populations.
To start, the mental health responses were bleak: 75% reported anxiety symptoms, with approximately 17% and 13% falling into moderate and severe categories. In addition, 53% of the students experienced sleep difficulties consistent with insomnia.
Startling findings aside, what they found in the blood samples were even more revealing.
- Students reporting anxiety symptoms had both lower numbers and lower percentages of circulating NK cells, including the most protective cytotoxic subtypes.
- The severity mattered: Mild anxiety showed minimal, non-significant changes, whereas moderate to severe anxiety was linked to a notably reduced proportion of NK cells
- Sleep issues compounded the issue. Among students with sleep disturbances, higher anxiety scores were associated with an even greater decline in total peripheral NK cells.
This suggests a close relationship—more psychological stress, fewer immune defenders.
Important limitations to keep in mind
How to support your body (and immune system) through stress
While no single habit can “fix” stress, previous research consistently shows that certain lifestyle habits can improve your body’s response to stress, both acute and chronic.
- Regular physical movement: Exercise has been shown in robust research to improve mental resilience, particularly as it relates to anxiety, depression, and even sleep.
- Practices that calm the nervous system: Studies have shown that meditation, breathwork, and yoga all contribute to improved mental health.
- A balanced, nutrient-dense diet: The gut is both our “second brain”and one of the most critical immune organs—making diet a particularly important part of stress and immunity management. For an extra immune system boost, try these 23 foods.
Ultimately, supporting mental health—and by extension immune health—requires a full-body approach. Managing stress isn’t about eliminating it entirely, but about building daily practices that support nervous system balance, sleep quality, movement, and nourishment. When those systems are supported together, the immune system is better equipped to do its job.
Related read: 13 habits to support your immune system this cold & flu season
The takeaway
We tend to think of stress as something that lives in the mind. Racing thoughts. Shallow sleep. That constant edge you can’t quite shake. But new research suggests stress may also be quietly reshaping your immune system in serious and meaningful ways that leave your body more vulnerable to illness and long-term health risks.
This study is a reminder that having reliable, consistent stress management practices isn’t just for your emotional or mental well-being—it can help your whole body flourish in the immediate and long-term.