September can leave your immune system in tatters. Find out how certain foods could help

Which vitamins are important for immunity?

The relationship between nutrition and immunity is incredibly complex – and only a small part of the puzzle. We know our immune system can be affected by various factors such as age, gender, lifestyle, vaccination status to name a few – diet is just one other factor. While you could be eating a well balanced diet to help promote a strong immune system, other factors can still come into play and result in illness anyway. That said, poor nutritional status can lead to a weakened immune system, so prioritising healthy food choices can help you maintain good immunity.

There are specific nutrients known to play a vital role in immunity, and these are all approved by the EFSA (European Food Safety Authority) to carry the label 'contributes to the normal functioning of the immune system'. What this means is that these nutrients play an essential role within our immune system – but it doesn't necessarily mean that having more than the required level can 'boost' our immune system. We'll discuss this in more detail later.

Here's a list of the nutrients which carry the EFSA claim and some great food sources:

Vitamin A

Eggs, liver, milk, cheese, yogurt, fortified spreads, sweet potatoes, carrots, bell peppers, papaya, mango

Vitamin B6

Poultry, oily fish, dark leafy greens, bananas, papaya, oranges

Vitamin B12

Meat, poultry, eggs, dairy products

Vitamin C

Citrus fruits, bell peppers, green leafy vegetables, potatoes

Vitamin D

Eggs, oily fish, fortified drinks, spreads and breakfast cereals

Copper

Nuts, shellfish, offal

Iron

Liver, red meat, beans, nuts, dried fruit, fortified breakfast cereals

Selenium

Brazil nuts, fish, meat, eggs

Zinc

Meat, shellfish, dairy, bread, cereal products

Having a variety of foods in your diet, which include some of the food options above, should ensure you reach the required intakes for each vitamin and mineral. This is the best way to ensure your immune system can work efficiently.

That's not to say other nutrients aren't important for keeping us well however, for example vitamin E is an antioxidant, so it can help fight off harmful free radicals that can damage our cells. Ultimately, eating a varied diet is best to ensure you are getting a mix of all important nutrients.

What should I eat to recover faster?

Many of us like to 'dose up' on vitamin C when we have a cold, as we're told it will help us get better faster. Zinc is another mineral usually present in any supplement marketed to 'boost' immunity. But does more of these nutrients actually speed up our recovery when we have a virus such as a cold? The research is mixed.

Vitamin C and zinc supplementation

One study looked at the effect of high dose supplementation with vitamin C and zinc on the length of symptoms in 214 men and women with diagnosed coronavirus [1]. It was found that subjects in the control group took an average of 6.7 days to reach a 50% reduction in symptoms. Those supplemented with vitamin C took 5.5 days, those taking zinc took 5.9 days and those supplemented with both took 5.5 days. These slight differences were not found to be statistically significant, so the researchers concluded that vitamin C and zinc supplementation does not reduce the length of respiratory infections such as coronavirus.

Conversely a research review looking at 29 studies investigating vitamin C supplementation in the prevention and recovery of common colds, concluded that supplementing with vitamin C wouldn't stop you catching a cold, but could decrease the duration of the cold by around 10% [2].

It seems well accepted that in people who are generally well and not deficient in vitamin C, dosing up on vitamin C with a high dose supplement will not prevent them from catching a cold. But, it's possible that once ill, extra vitamin C could help us fight off the virus a little faster. The same may also be true of zinc. One explanation could be that once we're ill, our body's requirement for vitamin C and zinc increases, along with the need for extra energy for example, so taking in more during the period of illness could help our immune system work more efficiently!

To eat or not to eat when ill

Again, the research around this is mixed, and it's not entirely clear if stocking up on nutrient dense food or fasting is best for recovery, as both may have benefits. For most of us, our appetite governs what we eat when we're under the weather. You either lose the desire for food completely, or only really fancy certain things. It's likely that we should pay attention to our body's cues and eat well if we can, but if not, just focusing on fluids is fine. Once you've recovered, you can make up for any loss of energy intake by eating a little more – bonus!

Top tips when feeling unwell

1. Drink plenty of fluids.
2. Follow your hunger cues.
3. Extra vitamin C and zinc may help you fight off a cold a little faster.
4. Focus on nutrient dense foods if you can eat.
5. Take it easy!

What should I eat to stay well generally?

Without doubt, being deficient in certain vitamins and minerals can lead to illness, because our immune system needs specific nutrients to function correctly. But this doesn't necessarily mean that having excess amounts of these nutrients is better than just having what we need.

Dosing up on vitamins to avoid illness

In reality, the idea we can give ourselves some sort of super immunity by taking heavy doses of nutrients is a little misleading. As was concluded in the research review I mentioned above, vitamin C supplementation over time was not found to reduce the chances of catching a cold [2]. In fact, taking too much of certain nutrients in supplement form can actually be detrimental to our immune system and general health – e.g. fat soluble vitamins A and E can build up in our system and become harmful [3]. It's about striking a balance and having an adequate amount each day, and this can be achieved through eating a varied and healthy diet for the majority of us.

Vitamin D and immunity

An interesting topic these days is vitamin D and immunity. We've long known that vitamin D is important for bone health, but it's essential role in immunity is a more recent discovery. In the UK, all of us are recommended to consider taking a vitamin D supplement in the autumn and winter months, to ensure we have adequate levels in our body. This is because we can't make the vitamin D we need from sunlight exposure during these months, and the food sources of vitamin D are fairly limited.

While vitamin D deficiency has long been known to affect bone health, more recent research highlights its role in immunity. A meta-analysis looking at the results of 8 large cohort studies concluded that low levels of vitamin D increased all-cause mortality risk when compared to people who had higher levels [4]. These findings are fascinating, and highlight the need for adequate vitamin D levels in the body to protect many aspects of health – not just bone health.

Our gut and long-term health

So you may be aware that our gut health is a hot topic right now, as we're becoming more aware of the impact of our gut on a multitude of health factors. And guess what? Our immune system is no different. It's no wonder our gut plays a key role in immunity, when you consider everything we eat must be handled by our gut. It's also estimated that around 70% of our immune cells are present in our gut!

Research has shown that a more diverse gut microbiome is associated with better immunity [5]. We know that our dietary choices can affect the diversity of our gut microbiome, so nutrition and immunity is strongly linked in this instance. A recent study found that aiming for at least 30 different varieties of plant-based foods in your diet each week is the best way to promote a more diverse gut microbiome [6]. Variety promotes variety!

Tops tips for a healthy immune system

1. Aim for a healthy balanced diet most of the time, rich in fruits, vegetables, wholegrains, nuts, seeds, fish, dairy foods, eggs and lean protein such as chicken.
2. Diet diversity is key, so aim to include a variety of plant foods in your diet every week.
3. Consider taking a 10 microgram daily vitamin D supplement during autumn and winter.
4. Avoid extreme diet approaches – major reduction in calories can weaken immunity.
5. Limit intake of processed foods and excessive alcohol.
6. Drink plenty of fluids!