Stress can have a huge impact on different parts of our bodies - from the brain to the gut.
Whether you're stressed at work, stressed about money or stressed out by your kids, it seems like regularly feeling this way is something many of us live with and accept as part of life. But long-term stress can have a surprisingly big impact on different parts of our bodies.
People aged 25-34 are more stressed than the rest of the population, according to research by The Priory Group, with anxiety related to student debt, rising rents, getting on the housing ladder and starting a family.
When we feel stress, the body produces a surge of adrenaline and the hormone cortisol, which is needed as a 'fight or flight' defence mechanism (had our hunter-gatherer ancestors been calm all of the time, the human race wouldn't have survived very long).
Dr Dimitrios Paschos, consultant psychiatrist at Re:Cognitional Health (www.recognitionhealth.com), explains what happens when we feel stress. "The heart starts pumping faster and breathing is accelerated too. The aim is to boost the legs and the arms with freshly oxygenated blood. The pupils open wider, vision becomes sharper and powerful stress hormones - like noradrenaline and cortisol - are secreted, kick-starting a cascade of biological reactions to increase energy supply and prepare the body for various types of threats."
Our brains are part of this response to perceived danger too. "Under immediate threat, intellectual and analytical areas shut down to give way to signals from more primitive centres," says Dr Paschos. "But as stress hormones keep rising, the whole mechanism goes into overdrive, which can turn into panic and confusion. Logical thinking is literally suspended in high arousal states, which explains why panicking people often run towards the wrong exit."
So what happens if our brains respond like this on a chronic, long-term basis? "Whether prolonged stress is physical, psychological, social, financial or occupational, it still features as a top trigger for developing a psychiatric illness. There is hardly a mental health condition that doesn't involve anxiety symptoms. OCD, PTSD, phobias, panic disorder, generalised anxiety disorder, body image disorders and often depression all involve severe and persistent feelings of anxiety, worry and fear," says Dr Paschos.
As well as triggering long-term mental health conditions, stress can also significantly change the structure of your brain.
Dr Sarita Robinson, senior lecturer in psychology at the University of Central Lancashire, says: "Research has highlighted changes in the structure of the brain as a result of exposure to stress. The hippocampus, the part of the brain that is mainly associated with long-term memory, has been found to be a malleable part of the central organ, and some researchers suggest that it is particularly susceptible to the impact of long-term stress."
The immune system
Short bursts of cortisol aren't dangerous, and are actually helpful when we need to protect ourselves, but having high levels for a prolonged period of time can weaken the immune system.
Dr Clare Morrison, GP at online doctor and pharmacy Med Express (www.medexpress.co.uk), says: "[When we're stressed] adrenaline and cortisol chemicals cause blood to be pumped to our muscles and brain. Unfortunately, this means that resources are diverted away from the rest of the body, including the immune system.
"Cortisol suppresses inflammation during a response to stress, but if it's present in the body for long periods, we can develop a resistance to it - meaning we stop responding to it properly."
Dr Morrison says: "Depriving the immune system over a long period of time can lead to infection or even cancer. In addition, the body doesn't heal properly, increasing the time it takes to recover from degenerative problems and muscle strains."
Stress doesn't directly cause cardiovascular disease, but it is possible that it increases your risk level for different heart conditions, as it raises blood pressure and heart rate. "This puts a strain on the arteries and the heart, leading to higher risk of coronary heart disease and heart failure," says Dr Morrison.
"The elevated cortisol levels associated with stress, including working night shifts or long hours, for example, have been shown to increase the tendency to 'metabolic syndrome', which is linked to hypertension, diabetes, raised cholesterol, central obesity and blocked arteries."
The digestive system
Most digestive problems are to do with lifestyle, the foods we eat, or stress, according the NHS website. Digestion is controlled by the enteric nervous system, which is made up of hundreds of millions of nerves that communicate with the central nervous system. This often becomes inhibited during times of stress.
"Stress can impact every part of the digestive system," says Dr Mark Winwood (www.axappphealthcare.co.uk). "When stress activates the 'flight or fight' response in your central nervous system, digestion can slow, because your central nervous system shuts down blood flow, affects the contractions of your digestive muscles, and decreases secretions needed for digestion. Stress can cause inflammation of the gastrointestinal system, making you more susceptible to infection. We know the impact of long-term stress on the digestive system can lead to Irritable Bowel Syndrome (IBS)."
Dr Morrison adds: "[Stress] leads to too much acid in the stomach, causing dyspepsia, heartburn or even stomach ulcers. In the bowel, stress can lead to irritable bowel disease, causing diarrhoea, abdominal cramps and loss of appetite, for example."
"The oesophagus can also go into spasm when we are stressed, and there's the potential for malabsorption and loss of fluids."
Dr Adam Simon, chief medical officer at Push Doctor (www.pushdoctor.co.uk) says: "The longer you leave stress untreated, the worse these digestive issues can become. This can obviously have a significant impact on your day-to-day life.
"However, the important thing to remember is that most of these digestive symptoms can be improved, or even reversed, by tackling the source of your stress."