The UK has seen a surge in the sale of “mind, body, spirit books” in a “mindfulness mega-trend”, indicating a rising interest in managing the stresses of daily life. For example the meditation app, ‘Headspace’, has grown so popular that it has now been downloaded over 11 million times and is valued by Forbes at an estimated $250 million. So, do mindfulness and other stress-reduction practices really reduce stress?
As part of BBC’s Trust Me I’m a Doctor mental health special and Channel 4’s Live Well for Longer Dr. Nina Smyth and I have been able to evaluate the anti-stress effects of mindfulness practice, workplace yoga, the Green Gym and community choir singing.
How the ‘stress hormone’ cortisol works
Known as the ‘stress hormone’, cortisol affects virtually every cell in the body giving it a diverse set of actions ranging from effects on blood pressure, stored reserves of energy and the balance of the immune system. Cortisol regulates these systems in non-stressful day-to-day living as well as in response to a stressor.
Healthy cortisol secretion shows a marked 24-hour cycle with peak levels at about 30 minutes after waking and then declining throughout the day. The lowest levels are in the evening, reaching its lowest point during the early phases of sleep. This dynamically changing daily pattern is controlled by the body clock in the brain and is vital for informing other body systems when it is night and day so that they can operate to maximum efficiency.
Cortisol levels peak at about 30 minutes after awakening in healthy cortisol secretion cycles.
Stressful events trigger short bursts of cortisol secretion superimposed upon these daily cycles and, although adaptive in the short-term, exposure to stress over long periods with repeated bursts of cortisol secretion disrupts the healthy daily cortisol cycle. Resultant 24-hour cortisol profiles are flattened, meaning lower morning peaks, less decline over the day, and higher evening and night time levels. These flattened daily dynamics of cortisol secretion have been linked to ageing, clinical depression and a range of stress-related physical ill health such as cardiovascular disease.
The increase in cortisol to its daily peak after waking is particularly interesting. This marked surge in secretion (~100% increase) in the first 30 minutes after waking up is called the ‘cortisol awakening response’ (CAR) and is thought to prime us for the day ahead. It is flattened with repeated stress and increasing age, and we have shown that this flattening has been linked with less efficient cognitive function as well as worse general health.
Measuring the ‘cortisol awakening response’
Cortisol can be measured in saliva samples and used as a biomarker of stress. Using these biomarkers, we measured the effectiveness of a range of stress management interventions. Using saliva samples gives an accurate index of blood levels and provides the opportunity for self-collection in naturalistic settings without the need to visit the laboratory.
There is extensive research on the CAR but unfortunately its measurement has been blighted by methodological problems. The CAR can be easily measured in saliva in the home environment, but to capture the rapid increase in the hormone, sampling at precises timings is essential at: 0, 15, 30 and 45 minutes after awakening. Sampling following awakening is bound to be problematic! Even well-intended participants are likely to be groggy immediately after awakening, leading to errors in sample timing.
Our research has been to define the effects of saliva sample timing delay and inform international guidelines that ensure reliable CAR measurement. Without application of this knowledge, investigation of the CAR and its effects on health cannot meaningfully progress. These strict methodological processes were applied here so we can be confident the results were not due to methodological error.
Reductions in stress, depression and anxiety
The body clock informs other body systems when it is night and day so that they can operate to maximum efficiency.
In short, we found that eight weeks of mindfulness practice, weekly workplace yoga sessions and weekly group Green Gym interventions produced marked reductions in self-reported stress, depression and anxiety compared to a matched no intervention control group. Crucially, the accurately measured CAR also increased in those that had been in the intervention groups – but the key finding was that this increase was only apparent in those that had enjoyed the activity (42% larger CAR on average). Participation in an activity that was not enjoyed did not lead to any advantageous change in cortisol secretion. Likewise, participation in the group evening choir activity induced an immediate advantageous effect on salivary cortisol levels.
So, the message is clear. Exposure to long-term stress affects daily patterns of cortisol secretion which, if left unchecked, can lead to stress-related ill health. However, participation in an activity that you enjoy (such as exercise, singing, mindfulness, gardening etc.) can minimise the negative impact of stress on health – as evidenced here by accurate assessment of cortisol in self-collected saliva samples.
Professor Angela Clow is Emeritus Professor of Psychology at the University of Westminster and is trained in neuropharmacology, physiology and psychology. Dr Nina Smyth is a Senior Lecturer of Psychology at the University of Westminster. Their research project ‘The Cortisol Awakening Response: Towards meaningful measurement’ was supported by a British Academy/Leverhulme Small Research Grant.