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Nutrition and immune function: Sorting fact from fiction

Article-Nutrition and immune function: Sorting fact from fiction

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Diets fuelled with the right vitamins and minerals are essential for our immune systems, whatever our age, to function at their best. However, the relationship between nutrition and our immune functions is highly complex. Overall nutritional status and dietary patterns (food, nutrients and non-nutritive bio-active compounds) impact the immune function. And the immune function also impacts on how our bodies metabolise vitamins and minerals from the diet, together with nutrient needs. The following overview by GP, Dr Gill Jenkins, from the evidence-backed Health & Food Supplements Information Service (HSIS) takes a look at what vitamins and minerals our immune systems need, together with current dietary shortfalls of these nutrients and busting information myths.


Micronutrients have vital roles throughout the immune system whatever your age. The vitamins and minerals needed to sustain a good, healthy immune function include:

  • Vitamin A, vitamin C, vitamin D, vitamin E, vitamin B2 (riboflavin), vitamin B6, vitamin B12, folate, iron, selenium and zinc.

Let’s take a look at a few of these nutrients and where there are dietary shortfalls and what this means to our health and wellbeing.

Poor immune nutrient intakes – the facts

Below-recommended intakes of nutrients involved in our immune functions are very common among many people, whatever their age in the UK. A 2019 report for HSIS[1] which evaluated micronutrient intakes from the UK NDNS[2] and DEFRA Family Food Survey over the last 20 years found there have been significant declines for several micronutrients during the past two decades. Intakes of riboflavin, folate, vitamin A, vitamin D, and iron significantly declined, while improvements were observed for zinc.  In particular:

  • Vitamin A intake has declined by 6.8 µg per day. Vitamin A is essential to help metabolise iron, maintain healthy mucous membranes, skin and vision, immune function and cell specialisation.
  • Vitamin D intake has reduced by a significant 22% over 20 years. Vitamin D is vital for normal bone, teeth, muscle and immune functions.

During the last nine years there has been a significant average yearly reduction in folate intake among men and women of all age groups including:

  • Around 3-4μg/day for children and adults aged 19 to 64 years
  • 5μg/day (equivalent to 45μg/day over the 9 years) for adults aged 65 years and over.
  • In 2014/2015 – 2015/2016, the NDNS showed that 15% of 11-18-year-old girls and 6% of 19-64-year-old women failed to achieve the Lower Reference Nutrient Intakes (LRNI) for folate. Blood folate concentrations also decreased significantly over the last nine years for most age groups whatever your gender.

Nutrient Spotlights:

The B Family

Folate/Folic Acid – the facts: Essential for the formation of red blood cells, folate has been shown to reduce the levels of an amino acid (homocysteine). This reduction may have a protective effect against heart disease too.1

Folate is also vital during pregnancy for efficient neural tube development which forms the brain and spinal cord. ‘Neural tube defects’, such as spina bifida in babies, appear to be linked to a ‘metabolic defect’ in folate metabolism in the mother. This means that, even though the mother may have an adequate dietary intake of folic acid, her body cannot use it efficiently. Taking extra folic acid at the time when the neural tube is forming can reduce the chance of the baby having a neural tube defect. However, the neural tube is formed very early during pregnancy – about a month after conception. Women are advised to take folic acid for 12 weeks prior to conception and to continue taking folic acid supplements until the 12th week of pregnancy.

Riboflavin (B2): Part of the B group of vitamins, Riboflavin is essential for the formation of two substances: FAD (flavin adenine dinucleotide) and FMN (flavin mononucleotide). Both are vital for the processes that make energy available in the body, essential for our immune systems. Riboflavin works effectively with iron, vitamin B6 and folic acid. It is important for the nervous system, skin and eye health too.

Vitamin D intakes – where are we?

Low vitamin D status is common in the UK. In the latest government survey—NDNS-RP—during January to March, 19% of children aged 4-10 years, 37% of children aged 11-18 years and 29% of adults had 25-OHD below 25nmol/L, the threshold indicating risk of deficiency. That’s why supplementation all year round is recommended and in particular, people should take 10 micrograms daily during the autumn and winter months as recommended by Public Health England.

Vitamin C – Spotlight

The facts:

  • Vitamin C (ascorbic acid) is a water-soluble, anti-oxidant vitamin. It cannot be made in the body and must be taken in the diet or in a dietary supplement.
  • It is present in foods including citrus fruits or their juices, tomatoes, red and green peppers, kiwi fruit, strawberries, broccoli and potatoes. Here’s a fast list of which foods are packed with vitamin C and how much of this vital nutrient in each of the following natural sources:
    • A clementine will provide about 30mg of vitamin C
    • 6 cherry tomatoes about 15mg of vitamin C
    • 1 kiwi fruit about 60mg of vitamin C
    • 1 cup of strawberries have around 90mg of vitamin C
    • 1 cup of peppers has about 120mg of vitamin C
    • 1 cup of broccoli has around 80mg of vitamin C
    • One 200g baked potato about 20mg of vitamin C
    • 100ml of orange juice about 50mg of vitamin C.

Vitamin C is found in high concentrations in phagocytes—the immune function cells—that help to fight infection. If the body develops an infection, the phagocytes are activated and release Reactive Oxygen Species (ROS). Whilst ROS appear to have a role in deactivating viruses and bacteria, they may also harm ordinary human cells. Vitamin C is a water-soluble antioxidant that may protect the ordinary human cells from damage by ROS. Some evidence indicates that vitamin C levels in the body may fall during infection.[3]

Vitamin C - the science in brief:

Laboratory studies have shown that vitamin C can help to alleviate infections but clinical human studies have shown that vitamin C does not reduce the incidence of common colds in the overall population neither does it treat colds once people have them. However, for people that are very physically active vitamin C has been shown to help reduce the number of colds.

There is also some evidence that vitamin C may help in other infections but research data is limited and there is no knowledge on appropriate dosage and timing over which vitamin C could be used in relation to an infection.[4]

How much vitamin C do we need?

The UK government guideline is for us all to achieve the Recommended Nutrient Intake of vitamin C at 40mg a day. This is set from a starting point that 10 mg/d of vitamin C is sufficient to prevent and to cure all the clinical signs of scurvy. But 10mg/day is not enough to give measurable plasma (blood) levels of the vitamin.

Myth busting on vitamin C and plasma levels:

Vitamin C begins to appear in plasma at intakes of about 30 mg/d and reaches a maximum concentration with intakes of about 70 mg/d. Significant amounts of vitamin C are present in plasma when intakes are 40 mg/d. The RNI has therefore been set at 40mg/day and the LRNI at 10mg/day.[5] The guidelines are based on the amount of vitamin C that will prevent the established adverse effects of vitamin C deficiency – i.e. scurvy and poor wound healing.

A daily amount of 40mg of vitamin C does not saturate the plasma levels. The vitamin C level in plasma of people in good health becomes saturated at about 70 micromol/L when the intake is about 200mg/day[i]. Below intakes of 100mg daily there is a steep relationship between dose and plasma concentration. This relationship flattens out between intakes of 100mg and 200mg daily. If regular intakes are below 100mg/day, the benefits could be expected from higher intakes on the basis of the intake/plasma concentration curve. However, infection itself causes altered vitamin C metabolism and vitamin C plasma levels may be decreased in cases of infection.

Sources of vitamin C

For people wanting to aim for a vitamin C intake of 200mg daily from their diet this would mean, consuming for example one cup of peppers and one cup of broccoli, 200ml of orange juice plus a cup of strawberries or one kiwi fruit, 12 cherry tomatoes and two clementines. Alternatively, a vitamin C supplement to bridge vitamin C gaps in the diet could be an option and vitamin C is also found in all multivitamin and multimineral supplements.

Minerals – the low down

Selenium intakes have changed little over the past decade but again, intakes fall well below recommended levels in some groups. In the latest government research - NDNS-RP - 26 per cent of 11-18-year olds, 25 per cent of 19-64-year-olds and 36 per cent of those aged 65 and over had selenium intakes below the LRNI. For women across these age ranges the figures were 45 per cent, 46 per cent and 66 per cent respectively. Again, LRNIs are bad news for people’s health and wellbeing and we all need selenium for a healthy immune system, thyroid function, protecting cells from oxidative stress and inflammation, as well as helping to keep hair and nails healthy.

Zinc intakes have improved slightly over the past 20 years although below-recommended intakes occur in some population groups. More than one in five (22 per cent) of 11-18-year olds, 11 per cent of 4-10-year old’s, eight per cent of 19-64-year olds and seven per cent of people 65 and over have a zinc intake below the LRNI. Amongst girls aged 11-18 years, more than a quarter (27 per cent) have a zinc intake below the LRNI. We need good zinc nutrient levels to fuel our bodies daily and this mineral helps with health functions such as:

  • Tissue growth
  • The growth of immune cells
  • The body to produce its own antioxidant enzymes
  • Fertility
  • Helping to keep hair, skin and nails healthy

Our iron scores – low or normal?

During the past 20 years, iron intakes have reduced by five per cent overall. We all really need iron in our diets to help ensure healthy immune systems and it also contributes to:

  • Normal energy metabolism
  • Cognitive function
  • Formation of red blood cells
  • Haemoglobin
  • Oxygen transport in the body
  • The reduction of tiredness and fatigue.

Some age and gender groups have mean intakes of iron below the Reference Nutrient Intakes (RNI) and substantial proportions with intakes below the LRNI, in particular girls aged 11 to 18 years and women aged 19 to 64 years. More than half (54 per cent) of girls aged 11-18 years and more than one quarter (27 per cent) of women aged 19-64 have intakes of iron below the LRNI. And such low scores are bad for our health and wellbeing, making us more vulnerable to problems like a compromised immune function and osteoporosis.

Last word

Micronutrients are important for our immune functions to work well. Therefore, low intakes, especially in those nutrients where we have levels below the LRNI, are bad news for our immune system and can impact it. Intakes of micronutrients should be maintained within recommended levels. Getting vital nutrients from the diet is essential and following government healthy eating guidelines is key for people’s good health. A multivitamin and multimineral supplement can help bridge nutrient gaps where dietary intakes are lacking and keep our immune systems healthy and fit.