Stress and immunity

It's been a rough winter this year for many of us, with a lot of illness around. And while diet, exercise, sleep and hygiene can all make a difference, Dr Marissa Kelaher says stress is an area that's not discussed much, despite the fact it has a huge effect on our immune system.

Studies looking at how stress affects immunity are intriguing and give us a better insight into the role of stress and health. Our sympathetic (fight or flight) nervous system communicates directly with our immune (lymphatic) tissue via nerve fibres. Even previous stress and trauma can be remembered by our immune system and is part of why there is such a strong link between stress and conditions like autoimmune disease and allergies.

Cortisol (our stress hormone) also impacts immunity by altering our immune response and white blood cells. Plus, stress affects immunity via its impact on our day-to-day life. When we are stressed, we are more likely to do things that are bad for our immune system (such as eating poorly, not sleeping, not exercising, withdrawing from social contact, and smoking or drinking alcohol.

Short and long-term stress affect us differently. Acute stresses (lasting a few minutes or hours) actually help our immunity by boosting immune cell numbers and activity. This is part of our survival response, as it helps our body cope with threat or injury. It's also how 'hormetic' stresses such as exercise, fasting, or cold-water bathing work by creating a short controlled stressor that stimulates our immune system.

Chronic stress has a very different effect, by suppressing immunity, and making us more likely to catch infections. This is why infections such as herpes or shingles can reactivate during times of stress.

One of the first studies looking at this was in the 1980s, where blood samples were taken from medical students before and during end of year exams. It showed that T cell and NK cell (white blood cell) levels dropped significantly under stress, and the severity correlated with stress levels.

Hundreds of studies have looked into stress and immunity since and have found similar effects, especially in older people, or people with depression. Another study looked at first year college students and found the higher their stress levels and the more socially isolated they were, the less they responded to a flu vaccine.

Fortunately, there are many proven ways to improve immunity when we're stressed - they all involve 'dialling down' our stress response.

The following have all been shown to reduce stress hormones, and measurably improve our immune function:

- journalling

- connecting with others

- meditation and breathwork

- exercise and time in nature

- sleep

In practice, most things that reduce stress are likely to help immunity, the key is having tools you can use, and making them part of your day-to-day life.