The Immunity Cookbook: How to Strengthen Your Immune System and Boost Long-Term Health, with 100 Easy Recipes

Stress can have a significant impact on both your mental and physical health, impacting immunity, and putting us at a greater risk of infection and disease. If you have been experiencing intense stress for a lengthy period, you may well be chronically stressed, putting you at a greater risk for developing autoimmune conditions.

In the early 1980s, researchers from the Ohio State University College of Medicine were intrigued by animal studies associating stress with infection, and for a decade they studied medical students and found that the students’ immunity decreased every year due to the stress of a three-day exam period⁹⁰. In addition, they noted that the students had fewer NK cells, which fight viral infections and tumours, and nearly stopped producing interferon, a cytokine that is crucial to innate and adaptive immunity.

Furthermore, a different team of researchers analyzed 300 studies on stress and health⁹¹ and detected interesting patterns. Studies that stressed people for a few minutes discovered a burst of one type of ‘first responder’ activity mixed with other signs of weakening. However, for recurrent and chronic stress of any prolonged period (from a few days to a few months or years), all aspects of immunity were adversely affected. In addition, the research showed that the participants who were already unwell or elderly were more susceptible to stress-associated immunity changes.

Managing chronic stress can help us to fight germs and strengthen our immunity. This was confirmed by researchers who compared the immune function of exam-stressed medical students given hypnosis and relaxation training with that of students without training. At first, the immune responses of the two groups both seemed to decrease; however, closer review highlighted that some of the students took this exercise more seriously than others. The students that were committed and consistent in their practice, did have significantly superior immune function during the exams than those who did not do the relaxation exercises, or performed them only intermittently.

Mind:body interaction is key. Research has shown that chronic feelings of loneliness can help to predict health status, maybe since lonely people experience greater psychological stress, or perhaps experience it more intensely. That stress then dampens down immunity and hampers the body’s ability to fight infection. Studies have confirmed the value of good friends, and even a few close friends have been shown to help someone feel connected and able to deal with stressful events. In fact, the presence of friends can make us view stress differently, as one study demonstrated⁹². The researchers asked participants who were either alone or with a friend to estimate the steepness of a hill in front of them. With no support close by, the participants who were on their own perceived the hill as steeper than the subjects who were accompanied by a friend.

Stress not only ravages our immunity, but it also wreaks havoc with our gut health, and it’s increasingly recognized that stress changes our gut microbiota community structure and also activity 93. In fact, it may be one causal factor in dysbiosis⁹⁴. Furthermore, psychological stress has also been associated with multiple GI disorders⁹⁵. We don’t fully know why yet, but the association appears to be attributed to stress-induced alterations in communication between the gut and the brain (the gut-brain axis), to include altered signalling along the vagus nerve and enteric nervous system; and HPA-axis activation resulting in immunomodulation, inflammation, intestinal damage, and increased GI permeability⁹¹. All of these factors have the potential to adversely impact the gut microbiota and our gut health.

In a mouse study, the researchers investigated how stress-induced alterations to the gut microbiome influence health. They observed that sharing a cage with more aggressive mice, which is considered a ‘social disruption’ stressor, decreased ‘good’ bacteria, reduced the overall diversity of the gut microbiome, and encouraged harmful bacteria to multiply. This resulted in the animals becoming more vulnerable to infection and having gut inflammation. In a follow-up study, the researchers found that administering mice broad-spectrum antibiotics to suppress gut bacteria inhibited stress-induced inflammation. Likewise, they reported that germ-free mice also didn’t show stress-induced inflammation, but when the germ-free mice were colonized with a normal population of bacteria, stress once again resulted in gut inflammation⁹⁶.

Stress-induced changes to the microbiome may also affect the brain and behaviour. A study conducted by Harvard Medical School reported that elite-level athletes who stayed calm during stressful sports competitions shared common gut microbiome traits, suggesting that there might well be an association between mental resilience and the gut microbiome.

There are several scientifically proven strategies for managing stress, including exercise, yoga, meditation, mindfulness, and by having healthy, positive friendships.

We know exercise is good for us on so many different levels, including promoting gut and immune health, as we saw in the last chapter. However, exercise is also an excellent ‘de-stressor’, and many people experience an immediate boost to their mood after exercise. Fortunately, those positive feelings don’t end there, but generally increase over time. So you are very likely to notice increased feelings of well-being if you commit to a regular exercise regimen. As well as reducing stress, regular physical activity benefits health in numerous other ways, which may indirectly help to reduce your stress levels. Exercise is also an effective way to help you sleep better at night.

The word ‘yoga’ comes from the Sanskrit word ‘yuji’, meaning yoke or union, and the practice of yoga unites mind and body. Yoga has been shown to modulate the stress response system, thereby reducing blood pressure, decreasing heart rate and regulating breathing. Several studies have highlighted that practising yoga can reduce cortisol levels, which we know produce many of the harmful effects of stress. One study demonstrated the impressive effect of yoga on stress by assessing 24 women who defined themselves as emotionally distressed. After a 12-week yoga programme, the women had significantly decreased cortisol levels. They also reported reduced stress, anxiety, fatigue and depression⁹⁷. A later study of 131 people had similar results, showing that 10 weeks of yoga helped to reduce stress and anxiety, while also improving quality of life and mental health⁹⁸.

Mindfulness is a state of intentional, nonjudgemental focus on the present moment. In a review of meditation studies¹⁰¹, the authors reported solid evidence that individuals who had mindfulness-based therapy during times of stress, were less prone to respond pessimistically. They also demonstrated that people who participated in mindfulness-based therapy or mindfulness-based stress reduction were more able to focus on the present and less likely to worry and to think about a negative thought or experience repeatedly. It is hypothesized that the beneficial effects of mindfulness are linked to its capacity to reduce the body’s stress response. We know that chronic stress can impair immunity, and contribute to the worsening of many other health problems. However, by reducing the stress response, mindfulness may have other beneficial effects throughout the body, including strengthening immunity.

Key points

Avoid prolonged chronic stress.
Adopt stress-management techniques that work for you – going for a walk, yoga, meditation or practising mindfulness.
Spend time with friends and laugh – laughter really is the best medicine!

As well as affecting your immunity and gut health, chronic stress can also lead to sleep problems. Stress and sleep go hand in hand, as we will discover in the next chapter.