Everyone knows if a car is running hot then you're heading for a breakdown.
But now there is strong evidence that it's the same for humans, too, with studies showing a significant link between chronic inflammation and serious health issues. Inflammation is an important part of our body's defence system. It mobilises the immune system to combat bacteria and other pathogens, or repair damage such as a sprained muscle.
That's why infections trigger a raised temperature and the site of an injury is often warmer to the touch than the surrounding healthy tissue. But when this short-term response does not deactivate properly, or unhealthy lifestyle choices keep it simmering away in the background, prolonged inflammation can increase your risk of cardiovascular disease, type-2 diabetes, arthritis, cancer and many other life-limiting problems.
One study estimated that three in five people will die as a result of diseases linked to chronic inflammation, and researchers warn that the numbers affected are expected to rise steadily, reports the Express. Another found 50 per cent of all deaths are caused by conditions linked with inflammation, and spotlighted the link to heart disease, stroke, cancer, diabetes, chronic kidney disease, non-alcoholic fatty liver disease and autoimmune and neurodegenerative conditions.
Professor Claire Bryant, a specialist in inflammation from the Department of Medicine at Cambridge University, has said: "We're very interested in trying to understand the causes of chronic inflammation in the context of many human diseases, and in particular the role of the inflammasome.
"What's become apparent over recent years is that one inflammasome in particular the NLRP3 inflammasome is very important in a number of major diseases such as obesity and atherosclerosis, but also in diseases like Alzheimer's and Parkinson's disease, many of the diseases of older age people, particularly in the Western world.
"Inflammation seems to underpin most diseases of old age. As we age, we also go into a condition called inflammaging, where you start to have higher markers for inflammation in the blood." This increase in inflammation as we age is associated with a decrease in muscle mass, bone strength and immunity, all of which are common signs of ageing.
Chronic inflammation can be identified by symptoms such as aches and pains, insomnia, chronic fatigue, depression and mood disorders, gastric issues like constipation, diarrhoea and acid reflux, weight fluctuations and frequent infections. However, research has shown that factors such as ageing, obesity, a diet high in refined sugar and saturated and trans-fats, smoking, stress and sleep disorders and low levels of sex hormones like oestrogen and testosterone can contribute to chronic inflammation.
Recognised links exist which can exacerbate these risk factors, creating a continuous cycle of inflammation. For example, a diet high in sugar and fat may lead to weight gain, and inadequate sleep has been linked with obesity, while hormone levels fall as we age. Professor Bryant said: "Inflammation can start to ramp up and get out of control, because once it starts, inflammation becomes a bit of a vicious cycle. You have to really interfere with that with medication and dietary and lifestyle changes."
Statins, well-known for reducing cholesterol, also lower inflammation, according to research. Scientists now think this is one reason why statins ward off hardening of the arteries and coronary heart disease.
Metformin, a common diabetes treatment, also quells chronic inflammation. Despite scientists still unravelling the mechanisms behind its anti-inflammatory action, a recent study claimed: "Metformin could be repurposed to address a range of complications, including inflammation, infections, and even cancer."
Research by Professor Bryant has uncovered an unexpected mechanism behind this decrease in inflammation. Fasting boosts levels of arachidonic acid, an omega-6 fatty acid, previously named as an instigator of inflammation. "We never expected that," she admits. "There could be a yin and yang effect going on here, whereby too much of the wrong thing is increasing your inflammasome activity and too little is decreasing it."
However, she warns there's still much to discover and cautions against fasting without consulting your GP. "There are a whole range of conditions, including diabetes, where you have to be very careful." Saturated fats are a no-go, not only because they boost the chances of being overweight, but also because they interfere with our immune system and increase the inflammasome activity which fuels inflammation.
Striking the right balance between omega-6 and omega-3 fatty acids seems crucial. About a century ago, the ratio of omega 6 to 3 in our diet was roughly four to one, but due to increased use of omega-6 fats, such as sunflower and soya oils, the ratio in a typical Western diet is now around 20 to one and some scientists reckon this encourages low-level inflammation.
The anti-inflammatory benefits of omega-3 are well known. Professor Philip Calder, a specialist in nutritional immunology at the University of Southampton, has demonstrated that two of the omega-3 fats in oily fish, DHA and EPA, "give rise to newly discovered resolvins which are anti-inflammatory and inflammation resolving".
Oxford University researchers have found that good sleep patterns can reduce the risk of death from cardiometabolic diseases, such as heart attacks, diabetes and strokes, by up to 39 per cent. They also found it can decrease the chance of dying from cancer by up to 19 per cent.
Inflammation appears to be a key factor in this. Poor sleep can increase our risk of obesity and cravings for foods high in saturated fats and sugar, contributing to a cycle of ongoing inflammation.
Short bursts of intense activity seem to be particularly beneficial, but even as little as 20 minutes of exercise a day has been shown to reduce inflammation. Resistance training is also proven to suppress inflammation, which aligns with NHS advice to engage in a mix of moderate activity for at least 150 hours a week.
Research shows that diets rich in animal products, processed food, sugar and alcohol boost levels of gut bacteria that promote inflammation. On the other hand, high-fibre plant-based foods and omega-3 fatty acids foster the growth of anti-inflammatory gut bacteria.
Lactobacillus casei, an ingredient found in several probiotic yogurts and drinks, is one of many friendly bacteria proven to reduce inflammation.