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Nutrition to Optimise Immune Function

Written By

Michael Betts


Nutrition, Personal Training

Posted On

25 November 2013

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Nutrition to Optimise Immune Function

Wendy Martinson, OBE, Bsc. (Hons) Nutrition Registered Dietitian & Sports Nutritionist (R.SEN)

A heavy schedule of exercise, plus the stresses and strains of today’s’ fast pace of life, can take its toll on our health. This can then increase susceptibility to common illnesses. The immune system has evolved to protect us against the many viruses, bacteria and parasites that attack our bodies on a day-to-day basis. This defence mechanism involves many different cell types and chemical messengers and its effectiveness can be influenced by a variety of factors. These include smoking, alcohol consumption, psychological stress, strenuous exercise, nutritional status, age, gut flora and genetics. (1)

The food and fluid we consume on a daily basis helps support the immune system and our ability to fight illness and infections. Here are some key nutrition strategies to help optimise the functioning of the immune system:

Nutrition to optimise immune function

1. Make sure all major food groups are included daily

This sound obvious, but sometimes it’s the obvious things that are missed. Nutritional deficiencies can impair immune function and so, by making sure you are including all food groups daily, this will limit the chances of this happening. Evidence shows that the prevalence or severity of many infections is increased by specific nutrient deficiencies. However, excessive intakes of individual micronutrients can also impair immune function. (2)

The macronutrients protein, carbohydrate and fat all play a role in maintaining immune system function. Inadequate protein intake can lead to impairment of cell replication and protein synthesis. These functions are necessary for the production of key immune cells (white blood cells) and soluble factors (chemical messenger proteins, which transmit messages between cells). It’s important to include good quality protein at mealtimes and in recovery snacks if training heavily. The quality of a protein is measured by its ease of digestion and its amino acid content. The digestibility and amino acid profiles tend to be lower in plant proteins. Good quality, high biological proteins can be found in meat, fish, poultry, eggs, milk and also soya.


Nutrition to optimise immune function

Both high fat and low fat diets may compromise immune function. An intake of approximately 20% energy from fat is the recommendation for athletes and active people. This guideline avoids either extreme. Omega 3 fats, found in oily fish (containing long chain omega 3 fats), linseeds, rapeseed oil, walnuts and omega 3 enriched eggs (containing short chain omega 3 fats), may be beneficial to immune function as they suppress the production of substances called prostaglandins, which may have immunosuppressive effects. In addition, the long chain omega 3 fats found in oily fish (salmon, trout, mackerel, sardines, pilchards, swordfish, fresh tuna, herring, kipper, eel, and whitebait), have been found to be the most potent in terms of health benefits. They are essential for brain and retina (eye) function and can help reduce the risk of heart disease. Aim for at least one 140g portion of oily fish per week and no more than two portions per week for women and four portions per week for men. Very high intakes of omega 3 fats can have immunosuppressive effects hence the avoidance of extreme intake is important. (3) Carbohydrate is an important fuel source for immune cells as well as being a key fuel during exercise. To maintain a robust immune function, include all food groups and avoid faddy restrictive diets.

Nutrition to optimise immune function

Major food groups

Bread, rice, potatoes, pasta and other starchy foods – eat with each meal & snack to boost carbohydrate intake Fruit and vegetables – eat at least 5 portions per day and a rainbow of colour Milk and dairy foods – eat at least 2-3 servings per day Meat, fish, eggs, beans and other non dairy sources of protein – eat at 2 -3 meals per day Foods and drinks high in fat and/or sugar – eat/drink in smaller amounts but include sports drinks at appropriate times

2. Use a carbohydrate/electrolyte drink during prolonged training of more than 60 - 90 minutes Research shows that exercising in a carbohydrate depleted state will increase stress hormone production, which in turn will suppress immune function. It is important to ensure a good carbohydrate intake when training regularly. It’s also a good idea to use a carbohydrate-containing drink e.g. sports drink providing 30-60g carbohydrate per hour during prolonged exercise. This will prevent blood glucose levels dropping too low. (2)

3. Stay hydrated and avoid getting a dry mouth during training Dehydration also increases stress hormone response and so adversely affects immune function. Keep a drink bottle with you during the day and drink enough fluid during training to minimise weight loss through sweat losses to 2% body weight. Drinking fluids during exercise will prevent getting a dry mouth by maintaining saliva secretion. This is important because saliva contains proteins with anti-microbial properties which help prevent the entry of illness-causing microbes into the body via the mouth. (2)

7. Include Vitamin C rich fruits and vegetables each day Vitamin C is necessary for a wide range of functions related to the immune system. Vitamin C is found in virtually all fruit and vegetables so include a wide variety each day. Especially good sources are sweet peppers, broccoli, watercress, tomatoes, blackcurrants, kiwi, citrus fruits, strawberries, and mango. A regular intake of 200mg Vitamin C per day will saturate the body so aim for a glass of fruit juice plus other rich sources below to achieve the optimal amount.


  • Vitamin C content
  • 200ml (medium glass) orange juice 78mg
  • 200ml apple juice 28mg
  • 200ml cranberry juice 60mg
  • 200ml pineapple juice 22mg
  • 1 medium orange 86mg
  • 1 kiwi fruit 35mg
  • ½ mango 28mg
  • Portion strawberries (120g) 92mg

There are times, for example, if you become exposed to a change in physical stress, when it may be useful to consider a vitamin C supplement. The 2007 Cochrane review on Vitamin C and the common cold, showed that taking at least 200mg of vitamin C per day had no effect on the incidence of the common cold in the ordinary population. What it did show however, was that the duration and severity of the cold symptoms were reduced. In addition, for those people exposed to short periods of extreme physical or cold stress, or both (e.g. marathon runners, skiers), vitamin C reduced the common cold risk by half (4). Therefore, it may be worth taking a vitamin C supplement if entering a period of high volume or intense training, or if training at altitude or in a hot environment. It should be noted that doses of vitamin C in excess of 1000mg per day can cause gastrointestinal side effects.

4. Include some ‘friendly bacteria’ in your diet regularly Probiotics (friendly bacteria) can have beneficial effects on gut microbial balance and can enhance the immune system. Dairy foods and yoghurt-type drinks with added probiotics are the easiest way to include these in your diet. Research on athletes is fairly limited, but some studies do show the benefit of probiotics on immune responses. In a double-blind, placebo controlled crossover trial, researchers gave 20 elite male distance runners a probiotic supplement over a four month period of winter training. The aim of this was to enhance immune function. Athletes taking the probiotic supplement reported less than half the number of days with respiratory (cold) symptoms compared to when they took the placebo. In addition to this, the severity of the illness was also lower for episodes of illness occurring during the probiotic treatment (5). Another study showed that fatigued athletes presenting impaired performance and lowered immune responses may benefit from probiotic (lactobacillus acidophilus) supplementation (6).

7. New research

Vitamin D It is widely known that vitamin D is required to maintain good bone health. There is now new evidence to suggest that vitamin D deficiency increases the risk of non- skeletal chronic diseases including cardiovascular disease, diabetes, hypertension and certain types of cancer. In addition, several recent studies have found that vitamin D status has a profound effect on human immunity.

Vitamin D is synthesised in the skin by the action of sunlight. Any factors limiting sun exposure can compromise vitamin D status including:

  • Aging (impairs synthetic ability)
  • Regular sunscreen use ( SPF≥15). One study showed SPF 8 reduced capacity to produce Vitamin D by 95%
  • Clothing
  • Cloud cover, atmospheric pollution
  • Time of day
  • Winter time latitude > 35◦ N or S

Dietary vitamin D includes vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol). Dietary sources include fatty fish, fortified margarine and some breakfast cereals. Vitamin D2 is 20-40% as effective as D3 at increasing and maintaining vitamin D concentrations. Diet only contributes a small proportion of Vitamin D requirements.

The association between Vitamin D and immunity is still emerging, but recent research has uncovered a direct link between vitamin D status and the release of disease-fighting antimicrobial peptides (AMPs). It is has been suggested that the ability of vitamin D to regulate the expression of AMPs in the epithelial cells of the respiratory tract could influence an individual’s susceptibility to the influenza virus. Preliminary data have suggested that three years of supplementation with vitamin D (800IU/20mcg for 2 years and 2000IU/50mcg for 1 additional year) reduced self reported incidence of influenza and the common cold and abolished seasonality of these infections (7).


Early research on a flavonol called quercetin, which is found in apples, onions, berries, leafy green vegetables, hot peppers, red grapes and black tea, has shown promising effects on the immune function. A double-blind study with 40 cyclists showed that taking1000mg a day of quercetin over a three week period, reduced the incidence of upper respiratory tract infection. This was during the two-week period following three days of exhaustive exercise. Scientists are doing further studies to find out more about how it works and how much is required for beneficial effects (8). For now, there’s another good reason to eat your 5 a day!

  1. Gleeson M. Immune function in sport and exercise. Churchill Livingstone, 2006
  2. Gleeson M, Nieman D, Pedersen B K, Exercise , nutrition and immune function J sports science 24 July 2006
  3. Burke L, Deakin V. Clinical Sports Nutrition 2006
  4. Douglas R M, et al. Vitamin C for preventing and treating the common cold. Cocrane review, 2007
  5. Cox A et al. Oral administration of the probiotic Lactobacillus fermentum VRI-003 and mucosal immunity in endurance athletes Br J Sports med Feb 2008
  6. Clancy R L, et al. Reversal in fatigued athletes of a defect in interferon γ secretion after administration of Lactobacillus acidophilus Br J Sports Med 2006;40;351-354
  7. Willis K S, et al Should we be concerned about the vitamin D status of athletes? Int J Sport Nut & exerc. met. 2008, 18,204-224
  8. Nieman D C et al. Quercetin reduces illness nut not immune perturbations after intensive exercise Exercise. Med. Sci. Sports Exerc. Vol 39 No 9 2007

Wendy Martinson OBE, profile

Wendy is currently the Lead Nutritionist for the Great Britain Rowing Team and Consultant Sports Nutritionist for British Gymnastics and Middlesex County Cricket Club. She combines this with her role as a part time Clinical Nutrition Manager in the NHS.

She has extensive experience working with elite athletes abroad having worked as the HQ Sports Nutritionist for Team GB at the 2008 Beijing Olympic Games. She was Consultant Sports Nutritionist to the British Olympic Association, having worked with British Gymnastics for over seven years. Wendy also acted as the Sports Nutritionist with World Class Hockey, the English National Ballet School and West Ham United FC in 2002, having consulted with the England Football Squad in preparation for the 2002 World Cup and Euro 2004.

As an FIE writer and presenter, to book Wendy for workshops, or to get in touch with Wendy, contact Fitness Industry Education on 0845 257 8570.

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