'Vitamins A and C can be found in a wide range of fruit and vegetables, whereas vitamin D, because it is fat soluble is found in food such as oily fish, dairy and eggs [see #4]. Zinc can also be sourced from these foods, as well as beans, pulses, nuts and seeds [see #10].
Indeed, a review of 83 clinical studies published in July this year in the American Journal Of Clinical Nutrition looked closely at the body of evidence on the subject and concluded that 'high intakes of fruits and vegetables lead to both a reduction in pro-inflammatory biomarkers [which can promote illness] and an enhanced immune cell profile.'
'A bright and colourful diet is often recommended to help support and boost the immune system,' says Isom.
'The colours within these foods are beneficial components, as well as their vitamin and mineral content,' she explains.
Especially helpful for immunity are plant pigments such as flavonoids found in rosehip, bilberry and other berries, carotenoids found in foods such as carrots and sweet potatoes, as well as rutin and hesperidin that are naturally found in citrus fruit, and lycopene naturally found in tomatoes, strawberries and cherries.
'These nutrients are antioxidant molecules that can prevent damage to cells and tissues, and reduce inflammation,' says Isom.
2. Get enough sleep
You have probably heard about the importance of getting enough sleep a million times before, but have you ever linked your insomnia problem to those recurring sore throats?
In a fascinating study published last year in the journal Sleep researchers took blood samples from 11 pairs of identical twins with different sleep patterns and discovered that the twin with shorter sleep duration had a depressed immune system, compared with his or her sibling.
'Sleep is our body's golden opportunity to rest and repair, and poor sleep is a common driver of a weakened immune system,' says Isom.
'Establishing a regular sleep-wake cycle – for example, 10pm sleep, 7am wake, avoiding technology in the hour or so before bed, and making sure you sleep in a dark room with blackout blinds and eye mask if needs be, alongside increasing your intake of calming nutrients such as magnesium and theanine, can be a great starting point,' she asserts.
The best sources of magnesium include green leafy vegetables, nuts, seeds, beans and pulses to name a few. 'However, for therapeutic levels we would recommend supplementation'.
'The best source of theanine is green tea,' says Isom. 'However, this may be stimulating for some individuals to consume before bed due to the caffeine levels in which case to help improve sleep, we would again recommend supplementation'.
It works for just about everything, but research has often been divided as to whether exercise can improve your immune system.
Some experts believe exercise can help release potential pathogens by keeping the lymphatic system moving, which encourages the body's detoxification through the lungs and skin through increased breath capacity and sweat. Any gym junkie will tell you they get fewer colds or just 'sweat them out.'
But while for years it was believed that strenuous exercise (the intensity and amounts elite athletes do) could dampen your immune system, a study from the University of Bath published in April this year in the journal Frontiers in Immunology challenged this idea.
The authors analysed the research available and reinterpreted it, concluding that intense exercise – instead of dampening immunity – may instead be beneficial for immune health.
The authors suggested that low numbers of immune cells in the bloodstream in the hours after exercise are – far from being a sign of immune-suppression – in fact a signal that these cells, primed by exercise, are working in other parts of the body, which has an immuno-protective effect.
According to Harvard Medical School, 'For now, even though a direct beneficial link hasn't been established, it's reasonable to consider moderate regular exercise to be a beneficial arrow in the quiver of healthy living, a potentially important means for keeping your immune system healthy along with the rest of your body'.
4. Take Vitamin D
Last year, a major global study published in the British Medical Journal suggested that adding more vitamin D to your diet could significantly cut NHS costs, by reducing the risk of colds, flu and other dangerous respiratory infections such as pneumonia and bronchitis.
The study, undertaken by Queen Mary University of London, reanalysed data from 25 clinical trials involving around 11,000 people from 14 countries.
The authors suggested their work settles the question of whether an increase in colds and flu in the winter is partly due to a vitamin D deficiency in the winter.
The consumption of vitamin D supplements daily or weekly showed an immunity benefit in everybody involved in the research, but particularly for those who have low levels, don't get outside much, cover themselves against the sun or for religious reasons, or have dark skins which absorb less sunlight.So what's going on?