If you search the internet for foods / nutrition to improve the immune system, you will be inundated with websites and supplement companies providing information and sales campaigns about foods / supplements, claiming they do wonders for the immune system. Many of these websites provide information about foods / supplements for which there is poor evidence, and claims which are dubious and misleading. So I thought I’d write a blog to sort the truth from the myths and fakes. As a registered Dietitian, you can trust the information you read is up to date and accurate.
Research has shown that deficiency of single nutrients can result in altered immune response – even when the deficiency state is relatively mild. Of the micronutrients, the following are important in immunity: zinc selenium, iron, copper, folic acid and vitamins A, C, E and B6.
Foods & nutrients which may help
Oily fish – Omega-3 fatty acids are perhaps one of the most researched nutrients when it comes to immunity. Omega-3 fats have been proven to decrease inflammation. The best, most potent source is from oily fish, e.g. salmon, mackerel, pilchards, sardines and fresh tuna. Including a portion (140g) of oily fish at least once a week can help.
Nuts & seeds – Omega-3 fats can also be found in some plant sources, namely linseeds (flaxseeds), linseed oil, brazil nuts, pumpkin and sesame seeds. Nuts and seeds are also a good source of selenium, a mineral used to make antioxidants (chemicals which help to protect the body from damaging ‘free radicals’), zinc, vitamin E and B vitamins.
Foods high in vitamin C – They say ‘an apple a day keeps the doctor away’…. Although this statement itself is a myth, apples, along with lots of other fruits and vegetables are a good source of vitamin C and other antioxidants. Vitamin C works to ‘mop up’ free radicals, to prevent damage to cells. Great sources of vitamin C include:
Citrus fruits (e.g. oranges, clementines, lemon, grapefruit)
Berries (e.g strawberries, blueberries and blackberries)
Watermelon and cantaloupe melon
Vegetables: spinach, broccoli and cabbage
Fruit juices – in particular, pomegranate juice is very high in antioxidants. A small glass a day, ideally with breakfast, is a healthy portion
The key is to make sure you’re having your 5-a-day – that’s 5 portions of fruit and vegetables a day, and while you’ve got a cold or flu, it’s a good idea to include a couple portion of fruits / vegetables high in vitamin C (from the list above).
Green leafy vegetables – Examples include spinach, sprouts, cabbage and broccoli – good sources of vitamin C and folic acid. They also contain small amount of alpha-linolenic acid, a type of omega-3 fatty acid.
Eating breakfast – They say ‘breakfast is the most important meal of the day’… and it really is! Not only will it help maintain your weight by breaking the night-time fast, and kickstarting your metabolism, but many breakfast cereals are fortified with added vitamins and minerals, including folic acid, selenium and zinc. Choose breakfast cereals containing less than 10g of sugar per 100g product to get more healthy benefits.
What about taking supplements?
The following table shows common supplements used to fight colds and flu or keep them at bay, or those ‘claimed’ to be helpful, along with a short summary of the evidence for each.
|Name of supplement||Summary of the evidence & cautionary notes|
|Antioxidants, including vitamin C, vitamin A, Vitamin E and selenium||Moderate is essential – vitamins A and E, for example, are stored in the body and eliminated slowly. Taking too much could be harmful.There is not enough evidence to support people taking antioxidant supplements – a major Cochrane review of the evidence (2012) found that overall, people taking antioxidant supplements were slightly more likely to die than those not taking supplements (this applied to both healthy people and those who had health conditions).|
|Zinc||A Cochrane review of the evidence (2011), suggests that taking zinc supplements within 1 day of symptoms starting will speed up recovery and reduce severity of symptoms. The NHS says that taking zinc syrup, tablets or lozenges, may effectively treat colds. Don’t take more than 25mg a day, unless advised by your doctor (if taken in too high a dose, zinc supplements may suppress the immune system)|
|Echinacea||A natural antibiotic and infection fighter by stimulating immune cells. Some evidence suggests that taking it at frequent intervals – every couple of hours – during acute infections may help as its effects are quite short-lived|
|Fish oils / omega-3 / DHA / EPA||Eating fish is the best way of obtaining the omega-3 fatty acids DHA and EPA. If you don’t eat oily fish or other sources of omega-3 fatty acids, you could consider a daily supplement, which could help keep colds at bay, although the evidence is inconclusive. They come in varying doses, and studies are inconclusive in terms of the best dose. Most studies have used doses around 500mg to 1g (1000mg) a day|
Other factors to keep illness at bay
Being a healthy weight – Being overweight or obese can reduce your immunity, meaning you may be more likely to suffer from colds and flu. Eating a healthy balanced diet – low in sugar, high in fruits, vegetables and wholegrain – with plenty of regular exercise can help reduce weight.
Being physically active – Studies show that regular exercise (the type that gets your heart rate going) – 30 minutes a day can increase your level of leukocytes – important cells that fight infection. If you don’t exercise, your risk of colds is higher than for people that exercise. We can know that feeling stressed also increases you chances of getting a cold. Regular exercise can help relieve stress too.
Eating foods high in sugar and fat – Studies suggest that eating too much sugar suppresses the immune system. Even drinking 2 x 330ml cans of fizzy drink (or the equivalent amount of sugar) a day can affect our immunity. A diet high in saturated fat has a similar effect. Foods high in saturated fat include butter, cream, cheese and fat/skin on meat.
The bottom line
There is no substitute for ‘real’ food! You body can absorb nutrients from real food much better than it can from supplements. Evidence suggests that eating a healthy balanced diet high in fruits, vegetables and wholegrains, and low in sugar and saturated fat can help optimise immunity. Maintaining a healthy weight and a regular physical activity routine is also important. If you are currently taking large doses of supplements or are concerned about what you’re taking, seek advice from a doctor, pharmacist or registered Dietitian.