Monday 19 December, 2022

Supporting the Immune System During Cancer

Jo is a Registered Dietitian & Founder of Green Light Nutrition. She has a passion for oncology and gastroenterology and supports a wide range of clients in order to reach their health goals.

It’s not new information that cancer can have an impact on the immune system. According to a poll we recently ran on our Instagram account, 90% of people who responded said they had struggled with nutrition since being diagnosed. One thing they wanted to know was how they could be supporting their immune system whilst going through cancer. 

To help answer this, we’ve enlisted the help of Jo Cunningham, Registered Dietician and owner of Green Light Nutrition. Jo specialises in supporting oncology and gastroenterology patients with their nutrition and has written this article for us, all about how to support the immune system.

First of all, I want to start off by saying that it’s not possible to “boost” the immune system, so be wary of anyone or anything that is making those claims as it tells me they don’t understand the science! Scientifically, if we were to boost our immune system, it would mean our immune system is overactive which can lead to autoimmune disorders. We want our immune system to be functioning normally, helping protect us from infection. There are definitely things we can do to “support” our immune system, which is what this article covers. 

The immune system and our gut

Did you know that 70% of the immune system cells are located in the gut? Inside our large intestine are trillions of beneficial bacteria and other microorganisms that work together to provide us with protection, nutrients and other health benefits. This inner community of microbes is referred to as the gut microbiome (GM). 

In the past 5 years there has been an increase in scientific research looking at the GM and how the makeup of the microbes may impact health, in terms of cancer formation as well as response to cancer treatment. Research suggests that the diversity within our GM may have a predictive ability when thinking about outcomes of cancer therapy, especially immunotherapy; i.e. the greater the diversity of microbes, the better the response to treatment.  Other studies indicate that our GM may also play a role in the severity of certain chemotherapy treatments, such as diarrhoea . 

It makes sense therefore, to focus on how we can look after this inner community of microbes. At the very least, you’ll be supporting your immune system throughout these bug-filled winter months!

So how do we nourish our microbes? A landmark study by the American Gut Project in 2018 found that those who had 30 or more plants per week had a more diverse range of gut bacteria vs those who had 10 or less plants per week. 30 sounds like a lot of plants, but when you break it down into the main food group categories it is more achievable than you might think.

This table shows you the food groups and a rough guide aim for:

Fruit2-3 pieces per day, spread out across the day instead of all at once. 
Vegetables5-7 different types per day, including salads, raw and cooked.
LegumesBeans, chickpeas and lentils can be added to soups, stews, and salads
Wholegrains3 different kinds e.g. oats, wholewheat bread, rice, quinoa, buckwheat
Nuts & Seeds1-2 types each day – whole, ground or nut butters all count
Herbs & SpicesAdd fresh, frozen, dried to your meals where possible

Rather than focusing on portion sizes, I recommend aiming for variety. You may find it helpful to count up how many different plants you’re getting in a week. If you’re anywhere near or over 30 then that’s great, but don’t be afraid to aim higher! If you’re not quite there yet, don’t worry – aim to gradually increase your variety each week by perhaps looking at which of the above six categories you’re not getting much diversity from. 

If you’d like some personalised tips then don’t hesitate to get in touch as gut health optimisation is something I support a lot of clients with in my clinic at Green Light Nutrition.

Other considerations

There’s some key nutrients that it’s important to discuss when it comes to immune system support. 

Vitamin D

An essential fat-soluble vitamin that plays a key role in supporting our bone health, data from human vitamin D supplementation studies have also shown beneficial effects of vitamin D on immune function. 

Shockingly, statistics suggest that 1 in 5 of the UK population has low levels of vitamin D, and that around half of the population aren’t aware of the recommendations for supplementation. 

The government recommends a daily supplement containing 400IU (10μg), however this amount aims to prevent severe deficiency and usually doesn’t provide enough to meet optimal levels. I tend to recommend 1000IU (25μg) to 3000IU (75μg) per day. For most adults, 4000IU (100μg) per day is considered safe but this should only be taken on the recommendation of your dietitian or GP. Ideally, you would tailor your supplement dose to your individual level by having your levels tested via your GP or oncology team on a 6 monthly basis. 

For more information on vitamin D including dietary sources (we can’t meet requirements through diet alone) take a look at my full article here

Vitamins A, C & E and selenium

These vitamins, as well as the mineral selenium, all have important roles when it comes to immune function as they have an antioxidant effect which means they defend us against “free radicals” which are chemicals that can damage cells as well as our genetic makeup. 

It’s really important to note that supplementation of high doses of antioxidants is NOT recommended during cancer treatment. This is because they may interfere with the medication which makes treatment less effective. The proposed theory is that they may be too protective of the cells that the treatment is trying to target. 

My advice is to get your antioxidants through food.  Lots of your plant foods contain these – aim for plenty of colour on your plate and across the week as outlined above and you’re likely getting everything you need. 

If you’re not able to eat enough then a multivitamin that contains no more than 100% NRV/RDA is deemed appropriate in most cases. If you’re not sure whether you can take something, always check with your oncology pharmacy team who have the expertise in this area. 


It’s never too late to introduce more plants into your diet. Our microbes like variety, so aim for plenty of different colours, textures and flavours across your week to nourish them, and in turn they will look after you. 

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