How does the immune system work and what can you do to support it, particularly during the cold and flu season? We bust some myths about 'boosting' the immune response and also ask the experts what you should do if you get recurrent viral infections and consistently feel below par.
It's easy to think of the immune system as a single entity, an internal 'deflection shield' that provides us with resistance to infection and toxins. In fact, it is a complex network of cells, tissues, and organs that work together through a series of processes to protect the body. The thymus, bone marrow and lymph nodes are key to immune function, as are our white blood cells (leukocytes) which seek out and fight off infection.
About 80% of our immune tissue lies within our digestive tract, acting as a protective barrier between our bloodstream and potential pathogens from the outside world, and the microbiome (the millions of micro-organisms and bacteria that live in our guts) is now a key area of scientific research; it has been shown to play a key role in immune response and overall health and fitness.
Innate and adaptive immune responses
The immune system can be split broadly into two parts which have very different functions - the innate and adaptive responses.
Professor James Brewer, chair of Basic Immunology at the University of Glasgow, explains:
"The innate system is what you're born with; it very rapidly tries to control the spread of an invading pathogen, giving your adaptive immune response time to mobilise and react against the specific infection you're faced with."
The innate response is what causes a high temperature, vomiting, mucus production and a streaming nose, as the body tries to quickly rid itself of the invader.
"The adaptive immune response is more specific," continues Brewer. "In your infant years you're generating millions of random, adaptive immune cells. These cells might be specific for dangerous challenges such as infection, or non-dangerous ones like food or body components such as insulin or joint tissues; it takes a while for your immune system to screen all these specificities and find the one that fits the infection you're faced with."
In most cases, once the immune system has found the specific fit that will eliminate the virus or bacteria, it will generate memory cells providing you with lifelong immunity to that particular infection.
When rhinoviruses (the virus that causes colds) replicate they rarely produce exact copies of themselves, which is part of their strategy for survival, and why we don't yet have a vaccine for the common cold.
"Another classic example is HIV," explains Brewer. "That's why an HIV vaccine is so difficult to develop, because there is so much variation in the virus."
Balance vs boost
Supplements and products that claim to boost the immune system are commonplace, but the popular concept of 'boosting' the immune system is largely misunderstood.
"It is usually inappropriate to boost the immune system," cautions Professor Charles Bangham, chair of Immunology at Imperial College London. "If someone is healthy and well-nourished, the immune system is balanced between its ability to recognise toxins, viruses and bacteria on the one hand, and making an inappropriate attack on the host's own tissues, ie an autoimmune response on the other."
The danger is that boosting the power of the immune response in a broad sense might increase the risk of autoimmune or allergic reactions. A more useful approach would be to support the immune system to remain in balance.
"When we talk about boosting the immune system it only makes sense if you boost it very specifically the way vaccines do," adds Brewer. "They are boosting a specific immune response to a particular infection."
Immune support - what works and what doesn't
From echinacea to nasal sprays and good old vitamin C, everyone has something they swear by to stave off colds, but many of these products are not supported by robust scientific evidence. So what has been proven actually to work?
"Diet plays an essential part in normal immune function, by ensuring that we have the necessary nutrients to allow the immune cells to work normally," says Bangham. "Vitamins can be helpful, but only if the person has an obvious deficiency, and probiotics might be helpful to restore a normal population of bacteria in the gut if the population has been altered by antibiotics. It seems clear that exercise, stress, a healthy sex life and adequate sleep also affect the efficiency of the immune response."
When we're stressed, the hormone corticosteroid is released: this can suppress the effectiveness of the immune system by lowering the number of lymphocytes. Lack of sleep has also been proven to affect the immune system - research shows that someone sleeping five to six hours a night has a far greater risk of catching a cold than someone who sleeps for seven hours.
"Sleep is an area of interest in immunology," says Brewer. "There's an increasing number of papers looking at circadian rhythms - the immune system seems to tune to what time of day it is. There was an interesting study a while back showing that if you vaccinated in the morning you would get better immune responses than later in the day, and suggesting that your immune system is heightened in the morning and starts to wane later on."
The tests to have if you're frequently ill
Indicators of serious immunodeficiency can include recurrent bouts of bronchitis and pneumonia, ear and sinus infections, meningitis, skin infections, blood disorders and infection of internal organs.
"There's no hard and fast National Institute for Health and Care Excellence (NICE) guidance for GPs regarding how to manage recurrent viral infections in patients," says Dr Tanya Lawson, General Practitioner for Dr Morton’s - the medical helpline. "Though in adults the cause of reduced immune response is likely to be due to another disease or deficiency that has an effect on the immune system, such as low thyroid hormone levels (hypothyroidism), type 2 diabetes, anaemia, or undiagnosed coeliac disease."
These conditions can be easily checked for by blood testing, but adults who present with recurrent infections can often pose a dilemma for GPs if no obvious immune deficiency can be established.
"It can be down to the usual suspects - lifestyle factors such as obesity, smoking, lack of exercise, excess alcohol and poor diet," says Lawson. "Asthma and allergies may also increase the frequency of recurrent mild infections, although they do not indicate an underlying impaired immune response."
Medication such as anti-autoimmune drugs and chemotherapy (during cancer treatment) can also impact upon immunity.
Children naturally suffer more mild self-limiting viral infections than adults and the frequency reduces with age (though in old age the immune system becomes less effective).
"At school, children will have around six or seven viral infections per year," continues Lawson. "If they have more frequent infections, especially if these are complicated by a bacterial infection requiring antibiotics, they should be investigated. And it is crucial that children are fully immunised against common diseases."
It is also important for the elderly and those who may be immune-suppressed to get the flu vaccine each year.
The answer may lie in your genes
If you're prone to frequent bugs and sniffles, yet all tests prove normal and you're living a healthy lifestyle, it might be down to your genes, says Brewer:
"It is very hard to analyse in detail why some people get ill more often than others, as so many factors are involved, but undoubtedly your genome influences your adaptive immune response."
"Inheritance plays a strong part in determining the type and power of the immune response," he concludes. "The particular genes that you carry determine how efficiently you will recognise each virus or bacterium, and your risk of autoimmunity and allergic diseases. It is now known that variation between people in these genes is the main reason why some become ill with a certain infectious agent, while others don't."