Nutrition and immune function

We are all aware of the role diet plays in dental caries and enamel erosion, but are we fully aware of the possible dietary implications on immune function and the progression of periodontal disease?

A number of factors can influence immune function. These include diet, how much exercise is taken, the environment in which we work and live, and our ability to manage stress. The immune system is also sensitive to alcohol consumption and smoking. It is not always possible to create the perfect environment for oneself, however it is possible to control our diet. Dietary influences can have either a positive or a negative effect on the immune system.

The relevance of this to us as dental professionals becomes apparent when we consider the biochemical and physiological importance of specific micronutrients in the regulation of cellular and humoral response indicated in the defence against bacterial colonisation, as well as the synthesis of prostaglandins in the regulation of the immuno-inflammatory pathways.

Immune-boosting nutrients

In order for our immune system to function effectively a number of key nutrients are required; these include adequate protein, fatty acids, the B vitamins and the antioxidants (vitamins A, C and E, and the minerals selenium and zinc).

Fatty acids

Linoleic acid and linolenic acid are essential dietary components for humans, as the body can synthesise the remainder fatty acids. Essential fatty acids deficiency is manifested by the inability to synthesise prostaglandins. Some of the best known mediators of the immuno-inflammatory pathways are prostaglandins. PGE1 and 3 are known to be anti-inflammatory and oppose the excess production of the pro-inflammatory PGE2. GLA works as an anti-inflammatory agent, blocking the mobilisation of arachidonic acid (AA). EPA from fish oils and its metabolites appear to compete with AA and so prevent the synthesis of AA to inflammatory metabolites. The prostaglandins group PGE2 and other metabolites of AA are released into gingival tissue in response to tissue damage, which in the progression of periodontal disease is caused by bacterial plaque.


One of the principal consequences of protein deficiency is an increased susceptibility to infection. Depressed immunoglobulin A (IgA, an antibody found in saliva), reduced immune cell activity such as phagocytic function and T-cell mediated responses may all facilitate susceptibility to infection peridontitis and alveolar bone loss. Adequate, good quality protein is therefore essential.

The B vitamins

The B vitamins are also implicated in the correct functioning of the immune cells. Vitamin B6 deficiency causes atrophy of the thymus, which produces T-cells. The spleen, which acts as a reservoir of immune cells, is also affected by a lack of Vitamin B6. This will result in a lack of antibody production. B5, B12 and folic acid are also needed for adequate T- and B-lymphocyte synthesis.

B vitamin deficiency symptoms are mainly seen to affect the oral tissues and facial skin. They include:

• Cracked lips

• Split nails

• Angular chelitis

• Burning feet

• Tender heels

• Dry scaling skin on the cheeks and forehead

• Tingling hands

• Eczema or dermatitis.

The antioxidants

Antioxidants protect cells from free radicals, which are potentially damaging by-products of oxygen metabolism that may contribute to the development of some chronic diseases.

Vitamin A

As an antioxidant, vitamin A helps to regulate the immune system, which, in turn, helps to prevent or fight off infections by making white blood cells that destroy harmful bacteria and viruses. Vitamin A may also help lymphocytes fight infections more effectively.

Vitamin A as retinol is found exclusively in animal products, however the body can also convert beta carotene (from red, yellow and orange fruit and vegetables) to vitamin A.

In vitamin A-deficient individuals, cells lining the lungs lose their ability to remove disease-causing micro-organisms. This may contribute to a susceptibility to upper respiratory tract infections. Deficiency symptoms may include apthous ulceration, acne and dry, flaky skin.

Vitamin C

Vitamin C tops the list of immune boosters for many reasons. Vitamin C increases the production of infection-fighting white blood cells and antibodies and increases levels of interferon, the antibody that coats cell surfaces, preventing the entry of viruses.

Vitamin C is involved in phagocytosis and can increase the resistance of tissues to infection. Vitamin C can be particularly low in smokers and those who do not eat fresh fruit and vegetables daily. Deficiency symptoms may include:

• Easy bruising

• Frequent colds or infections

• Nose bleeds

• Slow wound healing.

Vitamin E

This important antioxidant and immune booster does not get as much press as vitamin C, yet it is important for a healthy immune system. Vitamin E stimulates the production of natural killer cells, those that seek out and destroy germs and cancer cells. Vitamin E enhances the production of T- and B-cells, the immune cells that produce antibodies that destroy bacteria. Deficiency symptoms include frequent infections, easy bruising, slow wound healing, varicose veins and exhaustion.


This mineral increases natural killer cells and mobilises cancer-fighting cells. Selenium is incorporated into proteins to make selenoproteins, which are important antioxidant enzymes. The antioxidant properties of selenoproteins help to prevent cellular damage from free radicals. Other selenoproteins help to regulate thyroid function and play a role in the immune system.

Severe gastrointestinal disorders may decrease the absorption of selenium, resulting in selenium depletion or deficiency. Gastrointestinal problems that impair selenium absorption usually affect absorption of other nutrients as well.


This valuable mineral increases the production of white blood cells that fight infection and helps them fight more aggressively. It also increases killer cells that fight against cancer and helps white cells release more antibodies. Zinc increases the number of infection-fighting T-cells. Too much zinc, however (more than 75mg a day), can inhibit immune function. The recommended intake is 15mg daily.

Zinc deficiency symptoms include:

• Poor sense of taste or smell

• White flecks in fingernails

• Acne

• Frequent infections and poor wound healing.

Anti-immunity foods

Certain foods and dietary habits can work against the immune system, increasing our susceptibility to infections. These include refined carbohydrates, saturated fats, caffeine, alcohol and smoking.


Eating or drinking 100g (eight tablespoons) of sugar, the equivalent of one 330ml can of a fizzy drink, can reduce the ability of white blood cells to function by 40%. In addition, sugar depletes the body of B vitamins and zinc.

Saturated fats

An excess of saturated fats makes the lymphatic system sluggish and can impede production and function of prostaglandins, which are key regulators of inflammation and immunity. Saturated fats also slow the digestion and absorption of key micro nutrients, and are a source of free radicals. Obesity can lead to a depressed immune system. It can affect the ability of white blood cells to multiply, produce antibodies and rush to the site of an infection. Saturated fats are found mainly in animal fats such as meat, cheese, butter and cream.


Excess caffeine consumption can depress immunity as it acts as an adrenal stressor. The production of adrenaline and cortisol suppress the immune system. It acts as an anti-nutrient by blocking the absorption of nutrients from food, such as zinc and the B vitamins. Caffeine is found in tea, coffee, chocolate and some drinks such as Red Bull, as well as food and drink containing guarana.


Excessive alcohol intake can affect the immune system in two ways. It produces an overall nutritional deficiency, depriving the body of valuable immune-boosting nutrients, and alcohol, like sugar, consumed in excess can reduce the ability of white cells to function. High doses of alcohol suppress the ability of the white blood cells to multiply, inhibit the action of killer white cells on cancer cells, and lessen the ability of macrophages to produce tumour necrosis factors.

Damage to the immune system increases in proportion to the quantity of alcohol consumed. Amounts of alcohol that are enough to cause intoxication are also enough to suppress immunity.


One of the major reasons that smoking causes cancer is as a result of its immune suppressant activity. Cigarettes contain nicotine and cadmium plus 16 other chemicals, and they are a major source of free radicals, depleting antioxidant status.

Most smokers have elevated white blood cell counts due to underlying chronic infection, making them particularly prone to upper respiratory tract infections.

The immune-boosting diet

Always eat breakfast! Include whole grains, fruit, low fat dairy products, high fibre cereal and yoghurt, nuts and seeds, and fresh juices.

Have a mid-morning snack. Low blood sugar can depress immunity. Immune-boosting snacks include rye crackers, nut butter, corn chips, fresh fruit, cottage cheese or yoghurt, or a small handful nuts and seeds.

Lunch on the go can sometimes be a problem. However, fast food can also be nutritious food. Choose wholemeal bread sandwiches with a filling of chicken, tuna or low fat cheese plus salad vegetables. Alternatively, bring with you pasta or rice salad with lots of vegetables or beans, chickpeas and lentils. Finish off with a helping of fresh fruit for a power-packed lunch.

Having a mid-afternoon snack around 3pm, when energy levels begin to lag, will also boost your immunity. This should include nuts and seeds (sunflower, sesame or pumpkin, almonds and brazils), baby avocado or rye crackers with nut butter and fresh fruit.

A well-balanced evening meal will contain a good source of lean protein such as chicken, fish, lean beef or legumes (peas, beans and lentils); vegetarians can add nuts and seeds. Add fresh vegetables or a large green salad, plus wholegrain rice, pasta or potatoes with skins for extra nutrition. A moderate amount of alcohol and sweet puddings can also be enjoyed.

Coughs, colds and cold sores

When suffering from an infection, such as a cough or cold, avoid mucus-forming foods, which include milk and milk products and eggs. Anti-mucus foods include those with the sulphur amino acids methionine and cysteine, such as onions and garlic. A good antioxidant supplement will also be useful.

Colds sores (herpes simplex virus) have very specific reactions to certain nutrients. Avoid the amino acid arginine, which is found in peanuts, chocolate, seeds and cereals. Increase the amino acid lysine, which occurs in dairy products, beans, potatoes and eggs. A supplement of lysine at 1,000mg with vitamin C, E and zinc is also helpful.

There are many other factors that influence our ability to fight off infection and strengthen the immune system. Exercise, stress management and relaxation time are but a few.

In encouraging our patients to adopt a well-balanced, healthy diet it is clear that specific food choices are needed to facilitate more efficient absorption and utilisation of the micro-nutrients implicated in adequate immune function. We as healthcare professionals are in a position to dispense valuable nutritional advice. So next time our patients ask us for such advice, let’s not just resort to the well-balanced healthy diet!

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