By Lara Seago, Nutritional Therapist
To get you started, I would like to share with you some information regarding nutrition and lifestyle changes that may help to keep your immune systems strong and healthy.
First and to put this into context, let’s look at how the immune system works . . .
The main functions of human immune system are to protect us against infection from pathological microorganisms, to clear damaged tissues, and to provide constant surveillance of potentially malignant cells that grow within the body. The immune system also develops appropriate tolerance to avoid unwanted response to healthy tissues of self or harmless foreign substances. (Wu et al, 2019)
The skin, cornea, and mucosa of the respiratory, GI, and GU tracts form a physical barrier that is the body or immune system’s first line of defence. Some of these barriers also have active immune functions. If these barriers are breached, 2 types of immune response may occur…Innate immunity and adaptive immunity.
The innate immune system is the natural immunity we are born with and adaptive immunity is that which develops over time in response to exposure to antigens (Delves, 2018).
Frequent infections, autoimmunity, digestive complaints and fatigue are all common symptoms that may indicate a struggling immune system.
All human beings experience low immunity at various points in their lives and to varying degrees, from the common cold, to serious autoimmune diseases or even cancer.
While medications may help in certain circumstances, many people do not see this as the long-term solution and they understandably seek advice on how nutrition and lifestyle may be able to help.
Unfortunately, with increasing age comes a greater susceptibility to immune dysregulation and most older people above 60-65 experience immunity challenges to some degree. Ageing results in a loss of lymphoid tissue, particularly in the thymus, and the ability to respond to pathogens, antigens and mitogens decreases. Mucosal barriers also become impaired with age, resulting in weaker immunity. The development of long-term immune memory is affected, with a diminished response to vaccination. This mostly seems to affect adaptive immunity but also the innate immune system to a lesser extent (Maggini et al, 2018).
A diet rich in antioxidants which help to combat oxidative stress may help to slow down the ageing process and protect the immune system from more rapid decline. Supplementation may also be required in order to reach and maintain optimum nutrient levels.
How Might Nutrition Help to Support Immunity?
There is a wealth of research confirming the importance of good nutrition for a strong and healthy immune system.
Pae et al. (2012) highlighted the importance of optimal nutrition in maintaining a healthy immune system as we age.
A review by Maggini et al. (2018) supported the view that good nutrition is crucial for optimal immunity and suggested human nutritional requirements for a strong immune system are likely to change over the course of a life span. Sometimes diet alone is not enough and tailored supplementation is needed to bring the immune system back to peak condition. Registered Nutritional Therapists adopt this individualised approach to nutrition and supplementation, being mindful that no two people are the same and requirements will greatly vary depending on age, circumstances and many other variables. It is always advisable to seek advice regarding supplementation from a registered Nutritional Therapist before embarking on any regime.
Let’s look at some of the underlying imbalances that are often found in those with poor immunity or autoimmune conditions.
The immune system needs enough of the appropriate nutrients in order to function efficiently, ideally in optimum levels. If you would like guidance on how to test and clarify your levels, I recommended you speak with a Registered Nutritional Therapist who will be able to advise you.
Key micronutrients to consider for supporting immunity
The following are the key micronutrients instrumental in human immune function: –
Vitamin A is crucial for protecting epithelium and mucus integrity in the body. Vit A is known as an anti-inflammatory vitamin because of its critical role in enhancing immune function. Vit A is involved in the development of the immune system and plays regulatory roles in cellular immune responses, responsible for activating T-lymphocytes that are reactive against specific antigens and humoral immune processes, responsible for protecting us against toxins and pathogens (Huang et al, 2018, Britannica, 2020).
Vitamin C contributes to immune defence by supporting various cellular functions of both the innate and adaptive immune system. Vitamin C supports epithelial barrier function against pathogens and promotes the oxidant scavenging activity of the skin, thereby potentially protecting against environmental oxidative stress. Vitamin C deficiency results in impaired immunity and a higher susceptibility to infections. Supplementation with vitamin C appears to be able to both prevent and treat respiratory and systemic infections (Carr and Maggini, 2017). Vitamin C rich foods include citrus fruits, brightly coloured and green vegetables like peppers, tomatoes, sweet potato, papaya, strawberries, kale, cauliflower and broccoli (Web MD, 2020).
Small amounts of vitamin D can be obtained from egg yolks, liver, beef and fatty fish. However, our main source of Vitamin D is produced from the skin’s exposure to sunlight. Given the lack of sunshine is the UK, vitamin D deficiency is very common, particularly during the Winter months.
Studies have confirmed vitamin D has a positive impact on both innate and adaptive immunity and may also help to prevent or lessen autoimmune inflammatory diseases (Wu et al, 2019).
Although human studies are still lacking, animal studies have highlighted a clear link between Vitamin E deficiency and immune system impairment. Vitamin E is thought to enhance mucosal barrier integrity. Some studies have also shown a positive correlation between optimal vitamin E levels and reduced risk of developing influenza in the elderly (Wu et al, 2019), further supporting this potential correlation. Sources of vitamin E include: wheatgerm, hazelnut and sunflower oil, sunflower seeds, almonds, hazelnuts, brazil nuts, pine nuts, goose, salmon, trout, avocado, red peppers, mango and kiwi fruit (Arnarson, 2017).
Cobalamin (Vitamin B12) and folic acid (B9)
Evidence suggests that deficiency of folic acid and / or cobalamin can significantly impact on immunity by the production of nucleic acid, protein synthesis, inhibiting the activity of immune cells, and interfering with metabolic processes, including methylation. Inefficient methylation can lead to raised homocysteine levels which causes systemic and vascular inflammation, resulting in an immune response (Mikkelsen and Apostolopoulis, 2019).
Foods rich in B12 include liver, kidneys, clams, sardines, beef, nutritional yeast, trout, salmon, dairy and eggs (Semeco, 2020). Given that the majority of B12 rich foods come from animal sources, vegans are particularly vulnerable to B12 deficiency and may want to consider supplementation.
Foods rich in B9 include legumes, asparagus, eggs, leafy greens, beets, citrus, Brussel sprouts, broccoli, nuts and seeds, beef liver, papaya, wheatgerm, bananas and avocado (Link, 2020)
Zinc helps to maintain homeostasis of the immune system and its deficiency impacts on both innate and adaptive immunity. Deficiency of the essential mineral is particularly common in developing countries and amongst children and the elderly. This increases risk of infection amongst these deficient population groups. Interestingly 30% of the world’s population are said to be zinc deficient. (Wu et al, 2019).
Zinc rich foods include seafood, legumes, meat, nuts and seeds, dairy, eggs, wholegrains, potatoes, green beans, kale and dark chocolate (we know that last one is usually appreciated!) (West, 2018).
A review by Avery and Hoffmann (2018) concluded that a deficiency of selenium and selenoproteins (Selenium containing proteins) can impair both innate and adaptive immunity.
Selenium can be found in brazil nuts, cashews nuts, fish, ham, beef, turkey, chicken, cottage cheese, eggs, brown rice, sunflower seeds, mushrooms, cannellini beans, lentils, oatmeal, spinach, milk and yoghurt and bananas (Butler, 2018).
Essential fatty acids, particularly EPA and DHA derived from fish oil have been extensively researched and found to help modulate both innate and adaptive immunity. This is largely due to its powerful anti-inflammatory action (Wu et al, 2019).
The best source of EPA and DHA is oily fish like wild salmon, sardines and mackerel.
Green tea contains high content of catechins (around 10–15% of its dry weight) which include epicatechin (EC), epicatechin-3-gallate (ECG), epigallocatechin (EGC), and epigallocatechin-3-gallate (EGCG). EGCG is the most abundant and most biologically active, which is believed to be a primary factor responsible for green tea’s health benefit. Green tea and EGCG have been shown to be effective in modulating multiple aspects of innate and adaptive immunity (Wu et al, 2019)
Although the precise mechanisms of action are unknown, beta glucans have been found to have a powerful immunomodulatory effect, stimulating immune system cells and therefore helping to fight infection and even malignancies (Kim et al. 2011).
Beta-Glucans can be found in oats, barley, shitake and reishi mushrooms, seaweed and algae.
Malabsorption and how to support
Of course, it’s all very well eating a fantastic diet packed with all of these immune supporting nutrients, but if we are not digesting and absorbing them effectively they will not be have the impact on our immune system and overall health that we would like. A number of factors increase the likelihood of malabsorption, including: –
- damage to the intestine from a previous condition or surgery
- antibiotic use
- conditions such as coeliac disease, Crohn’s disease, cystic fibrosis and pancreatitis
- lactase deficiency or lactose intolerance
- diseases of the gall bladder, pancreas or liver
- intestinal parasites
- radiation therapy
- certain medications
- high alcohol intake
(Kerr and Cafasso, 2017)
Potential signs of malabsorption include anaemia, bloating, fatigue, stomach cramping, weakness and weight loss. If you think malabsorption may be an issue for you a registered nutritional therapist will be able to confirm this via a stool analysis.
What changes can we make to our diet to support our digestion?
Drinking apple cider vinegar diluted with water prior to meals, lemon water and eating pineapple and papaya may help. There are also several supplements helpful in supporting digestion and proper absorption.
Maximise your gut bacteria
There is lots of noise in the media these days about our microbiome and its importance. Our microbiome is the collection of billions of live bacteria in our gastrointestinal tract. An imbalance of bacteria in the gastrointestinal tract is very common (known as dysbiosis), and usually confirmed via a stool analysis. Unfortunately, dysbiosis of the microbiome can have a detrimental impact on immunity. Thankfully this can be resolved relatively easily by introducing probiotic rich foods into our daily diet. These include kimchi, kefir, sauerkraut, kombucha, tempeh, fermented miso and live yoghurt. Probiotic supplements may also be an effective way to re-populate the gut with beneficial bacteria. Probiotic intake reaches and interacts with the gut mucosa and mucosal immune system where the largest proportion of the body’s immune cells are found (around 80%). Probiotics modulate immune and inflammatory response in the gut through their interaction with intestinal epithelial cells. Studies also suggest that the beneficial impact probiotics have on the immune system is not restricted to the gut. Modulatory effects from probiotics have also been observed in the respiratory tract and findings suggest they could even support the systemic immune system, both innate and adaptive. Probiotics have been found to modulate inflammation and help to reduce or prevent allergies. (Wu et al, 2019).
Avoid food sensitivities
Food sensitivities may impact on the integrity of the mucosal barrier in the GI tract, which may in turn lead to an immune system reaction and inflammatory response. It is important to eliminate any foods you are sensitive to from your diet at least for a period. A Nutritional Therapist would be able to confirm any food intolerances and advise accordingly how best to proceed. Once the integrity of the GI tract and proper digestion is restored, it is sometimes possible to re-introduce foods. Common sensitivities include, wheat, dairy and eggs, although it is possible to develop sensitivities to any food.
Given that inflammation triggers a response from the immune system, it is important to reduce our inflammatory response as much as possible. Maintaining a healthy weight, keeping active, avoiding smoking or drinking excessively all help, along with sufficient, good quality sleep and relaxation are all helpful.
But what about diet? Well, of course there are lots of foods and nutrients found to have anti-inflammatory properties. Make sure you are including plenty of the following in your diet: –
- omega-3 fatty acids from oily fish, walnuts, flax and chia seeds
- antioxidants from a rainbow of fruits and vegetables
- anti-inflammatory herbs and spices like garlic, cumin, turmeric, ginger, rosemary
- quercetin rich foods which include red grapes, red apples and red onions
- resveratrol. This is where red wine comes in. Yes, is a great source. But please in moderation!
- optimising your vitamin D levels by getting out in the sunshine!
- magnesium rich foods, including dark chocolate, avocado, nuts, legumes, dark leafy green vegetables, tofu, seeds, wholegrains, salmon and bananas.
You may also wish to consider supplements for additional support. A Nutritional Therapist will be able to advise on which supplements are right for you.
Positive Lifestyle Changes to Support Immunity
Manage Your Stress Levels
Research indicates that psychological stress or trauma can dysregulate the human immune system and increase the possibility of developing chronic illnesses long-term or exacerbating existing ones (Morey et al, 2015).
Now, in the wake of COVID-19 and the world slowing down might be a good time to take a step back and review your work/ life balance. What small changes might be possible to reduce your stress levels? Gentle exercise like walking in nature and yoga is also helpful, and please remember to breathe! There are some great mindfulness apps you can download onto your phone for free. Try incorporating just 10 minutes per day into your routine and feel the difference. Epsom salt baths are also helpful for relaxation and for replacing some of that magnesium we tend to use excessively during stressful times.
If you are dealing with unresolved trauma, consider talking therapy via the Elysia Centre: talking therapies at elysia centre. This could be done remotely from the comfort of your own home.
Studies support the view that regular moderate to high intensity exercise most days for 30-60 minutes enhances immune system performance. However, be careful not to overdo it! Research also demonstrates increased immune system dysregulation and inflammation amongst athletes with intensive training schedules. (Neiman and Wentz, 2019). This activity doesn’t need to be formal exercise. Housework, gardening, walking the dog, cycling – they all count! Make the most of your daily opportunity to leave the house for exercise and make the most of getting out amongst nature.
Humans need between 7 and 9 hours of good quality sleep every night; and anything less than this has been proven to detrimentally affect the immune system. Many studies of healthy human volunteers subjected to sleep restriction or sleep deprivation demonstrate changes in circulating pro-inflammatory and anti-inflammatory cytokines, soluble receptors, inflammatory signalling pathways, and innate immunity (Opp and Krueger, 2015; Haack et al., 2004; Haack et al., 2007; Irwin et al., 2010; Lekander et al., 2013; Mullington et al., 2009; Mullington et al., 2010; Simpson and Dinges, 2007).
Practices for improving sleep include regular routines, getting daylight every morning and dimming the lights in the evenings, daily physical activity, stress management and relaxation techniques, avoiding caffeine and alcohol after midday, a hot bath before bed, ensuring the bedroom is sufficiently cool and dark and following a low-glycaemic diet.
Something else you may wish to try is including tart cherries in your diet before bed. Tart cherries are naturally rich in the sleep hormone melatonin so may be a helpful sleep aid.
Moderate Alcohol Levels
Before you get too excited about the potential benefits of resveratrol in red wine, it is also worth mentioning that there is much research highlighting the immunosuppressive effect alcohol has. Alcohol impacts on all aspects of the immune system, including structural human defence mechanisms in the gastrointestinal and respiratory tract as well as the innate and adaptive immune systems. The immune system is affected both by the direct impact of alcohol and through dysregulation of other components caused by alcohol (malabsorption of nutrients for example). (Molina, 2010).
We know how tempting it is to pour a drink or two, particularly at the moment when we are all stuck at home without the usual opportunities to socialise. But resist the temptation to go overboard! An occasional drink is usually fine but make sure you stay well within the recommended daily alcohol limits (2 to 3 units a day for women and 3 to 4 units for men) and have at least 2 to 3 alcohol-free days a week.
Smoking negatively impacts on both the innate and adaptive immune systems. It can cause a whole host of chronic illnesses from autoimmune, cardiovascular and respiratory diseases, to allergies and cancer. Cigarette smoke generally weakens immunity against infections but promotes autoimmunity. (Qui et al. 2017).
If you do not already smoke, then please avoid and if you do try to quit or at least cut down. For those of you looking for support to quit, free stop smoking services are available via the NHS:
Consider Toxic Exposure
New research shows that maternal exposure to industrial pollution can harm the immune system of offspring of subsequent generations, weakening the body’s defences against infections such as the influenza virus. (Post et al, 2019).
Of course, it is impossible to avoid toxic exposure altogether. We can’t avoid car fumes for example. But there are lots of environmental toxins / pollutants that can be controlled and minimised.
Try to keep your toxic load to a minimum by using non-toxic cleaning products, personal hygiene products and cosmetics, Avoiding Plastic wrapped food and plastic bottles, eating organic and filtering water. Increasing your intake of antioxidants may also help to combat potential free radical damage caused by pollutants / toxins.
Antioxidant Boosting Smoothie Recipes
Now, we know that including optimal amounts of fruit and vegetables into our diets can be hard work and difficult to achieve at times, particularly when juggling work, running a house with childcare and home-schooling, as many of us are in the current crisis.
A quick and convenient way to increase your antioxidant intake is to introduce plenty of juices and smoothies into your diet. They take minutes or sometimes even seconds to make and make a great breakfast or snack. You may even wish to consider adding some of those anti-inflammatory spices like turmeric and ginger.
Here are a few recipe suggestions to get you started.
Vitamins A to Zinc
A handful of rocket
1 yellow pepper
1 cup of strawberries
¼ cup of pumpkin seeds
Top up with water and blend
1 cm cube of ginger
A pinch of pink Himalayan salt or sea salt
2 tbsp raw honey
Top up with water and blend
1 red apple
1 cm cube of ginger
Squeeze of lime
Top up with water and blend
Handful of spinach
Handful of blueberries
Handful of macadamia nuts
1 tsp of cinnamon
1 tsp of turmeric
1 tbsp of maca powder
Top up with coconut milk and blend
For more information or to book a consultation with Nutrition for Vitality for your own personalised nutrition, lifestyle and supplement plan (all from the comfort of your own home), or for a FREE 15 minute discovery call, contact Lara Seago on [email protected] or 07887 943037.
Understanding that finances are currently tight for many, during the COVID-19 restrictions and until further notice, we will be offering all existing and new patients a 15% discount from our usual fees, so now is the time to take advantage! Let’s take control of our health and build our resilience.
Written by Lara Seago, Nutrition for Vitality (April 2020)
Avery, J and Hoffmann, P. (2018). Selenium, Selenoproteins, and Immunity. Department of Cell and Molecular Biology, John A. Burns School of Medicine, University of Hawaii. Available at: https://www.google.com/search?q=selenium+and+the+immune+system&ie=&oe= (Accessed 12/11/19)
Braun, L., Cohen, M (2007). Herbs & Natural Supplements. An evidence-based guide. 2nd Ed. Churchill Livingston: Elsevier
Butler, M.J. and Barrientos, R.M. (2020). The impact of nutrition on COVID-19 susceptibility and long-term consequences. Brain, Behaviour and Immunity. Available at: https://dx.doi.org/10.1016%2Fj.bbi.2020.04.040 (Accessed 27/04/20)
Campbell, J. & Turner J. (2018). Debunking the Myth of Exercise-Induced Immune Suppression: Redefining the Impact of Exercise on Immunological Health Across the Lifespan. Frontiers in Immunology. 9: 648. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5911985/ (Accessed 21/10/19)
Carr, A. & Maggini, S. (2017). Vitamin C and Immune Function. Nutrients. 9(11): 1211. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5707683/ (Accessed 05/11/19)
Chaplin, D. (2010). Overview of the Immune System. Journal of Clinical Immunology. 125(2 Suppl 2): S3–23. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2923430/ (Accessed 21/10/19)
Cheng, R. (2020). Successful High-Dose Vitamin C Treatment of Patients with Serious and Critical COVID-19 Infection. Orthomolecular.org. Available at: http://orthomolecular.org/resources/omns/v16n18.shtml?fbclid=IwAR3Uc6h2daErI82uep9wFN1wiBTUJI1RGIu8akDlPvRoJ-nV2Vgp0xxKJm8 (Accessed 27/04/20)
Cooper, E. & Ma, M. (2017). Understanding nutrition and immunity in disease management. Journal of Traditional and Complementary Medicine. 7(4): 386–391. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5634735/ (Accessed 07/11/19)
Davison, G. et al. (2014). Nutritional and Physical Activity Interventions to Improve Immunity. American Journal of Lifestyle Medicine. 10(3): 152–169. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6124954/ (Accessed 07/11/19)
Delves, P. (2018). Overview of the Immune System. MSD Manual: Professional Version. Available at: https://www.msdmanuals.com/en-gb/professional/immunology-allergic-disorders/biology-of-the-immune-system/overview-of-the-immune-system (Accessed 21/10/19)
Grant et al. (2020). Evidence that Vitamin D Supplementation Could Reduce Risk of Influenza and COVID-19 Infections and Deaths. Nutrients. 2;12(4). Available at: https://www.ncbi.nlm.nih.gov/pubmed/32252338?fbclid=IwAR3S8Ibso9Q1ImugH0Ts1_U8_9jSOC75zRXaS0R144WEd_-ZDjj-jtJFJnI (Accessed 27/04/20)
Guggenheim, et al. (2014). Immune Modulation From Five Major Mushrooms: Application to Integrative Oncology. Integrative Medicine: A Clinicians Journal. 13(1): 32–44. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4684115/ (Accessed 12/11/19)
Haack M. et al. (2004). Diurnal and sleep-wake dependent variations of soluble TNF- and IL-2 receptors in healthy volunteers. Brain Behav. Immun. 18:361–367. Available at: https://www.ncbi.nlm.nih.gov/pubmed/15157953 (Accessed 06/11/19)
Haack M. et al. (2007). Elevated inflammatory markers in response to prolonged sleep restriction are associated with increased pain experience in healthy volunteers. Sleep. 30:1145–1152. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1978405/ (Accessed 06/11/19)
Healthworld Australia (2009). Lactobacillus rhamnosus GG. Brisbane.
Hoffmann, P. & Berry, M. (2008). The influence of selenium on immune responses Molecular Nutrition and Food Research. 52(11): 1273–1280. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3723386/ (Accessed 06/11/19)
Huang, Z. et al. (2018). Role of Vitamin A in the Immune System. Journal of Clinical Medicine. 7(9): 258. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6162863/ (Accessed 27/03/20)
Irwin MR. et al. (2010). Sleep loss activates cellular markers of inflammation: sex differences. Brain Behav. Immun. 24:54–57. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2787978/ (Accessed 06/11/19)
Kim, H. et al. (2011). Stimulatory Effect of β-glucans on Immune Cells. Immune Network. 11(4): 191–195. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3202617/ (Accessed 12/11/19)
Lekander M. et al. (2013). Subjective health perception in healthy young men changes in response to experimentally restricted sleep and subsequent recovery sleep. Brain Behav. Immun. 34:43–46. Available at: https://www.ncbi.nlm.nih.gov/pubmed/23820239 (Accessed 06/11/19)
Maggini, S. et al. (2018). Immune Function and Micronutrient Requirements Change over the Life Course. Nutrients. 10(10): 1531. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6212925/ (Accessed 07/11/19)
Majamaa H, Isolauri E (1997). Probiotics: a novel approach in the management of food allergy. J Allergy Clin Immunolm. 99(2):179-85.
Mikkelson, K. and Apostolopoulis, V. (2019). Vitamin B12, Folic Acid, and the Immune System. Nutrition and Immunity. 103-114. Available at: https://link.springer.com/chapter/10.1007/978-3-030-16073-9_6 (Accessed 12/11/19)
Morey, J. et al. (2015). Current Directions in Stress and Human Immune Function. Current Opinion in Psychology. 5: 13–17. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4465119/ (Accessed 21/10/19)
Mullington JM. Et al. (2009). Cardiovascular, inflammatory, and metabolic consequences of sleep deprivation. Progress in Cardiovascular Diseases. 51:294–302. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3403737/ (Accessed 06/11/19)
Mullington JM. Et al. (2010). Sleep loss and inflammation. Best. Pract. Res. Clin. Endocrinol. Metab. 24:775–784. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3548567/ (Accessed 06/11/19)
Naja, F. and Hamadeh, R. (2020). Nutrition amid the COVID-19 pandemic: a multi-level framework for action. European Journal of Clinical Nutrition. Available at: https://www.nature.com/articles/s41430-020-0634-3?fbclid=IwAR1dWPfw_pLMiFv6v7sTe9tan2bgJMDr_kVhAAH2wQm2nLtIgGXc-zkBobE (Accessed 27/04/20)
Nantz M.P et al (2012) Supplementation with aged garlic extract improves both NK and γδ-T cell function and reduces the severity of cold and flu symptoms: A randomized, double-blind, placebo-controlled nutrition intervention, Clinical Nutrition Volume 31, Issue 3, Pages 337-344
Natural medicines comprehensive database. Natural medicines in the clinical management of cold and flu. http://www.naturaldatabase.com/(S(ezkgokmopdq0xl55sxvnk155))/ce/CECourse.aspx?cs=&pm=5&s=nd&pc=06-27&searchid=18031602#keywordanchor (Accessed 06/11/19)
Neiman, D. & Wentz, L. (2019). The compelling link between physical activity and the body’s defense system. Journal of Sport and Health Science. 8(3): 201–217. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6523821/ (Accessed 06/11/19)
Newman, T. (2018). How the Immune System works. Medical News Today. Available at: https://www.medicalnewstoday.com/articles/320101.php (Accessed 05/11/19)
Noss, I. et al. (2013). Comparison of the potency of a variety of β-glucans to induce cytokine production in human whole blood. Innate Immunity. 19(1): 10–19. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3976228/ (Accessed 06/11/19)
Opp, M & Krueger, J. (2015). Sleep and Immunity: A Growing Field with Clinical Impact. Brain, Behaviour and Immunity. 47: 1–3. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4685944/ (Accessed 06/11/19)
Pae, M. et al. (2012). The Role of Nutrition in Enhancing Immunity in Aging. Aging and Disease. 3(1): 91–129. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3320807/ (Accessed 07/11/19)
Post, C. et al. (2019). The Ancestral Environment Shapes Antiviral CD8+ T cell Responses across Generations. I Science. 20:168-183. Available at: https://www.cell.com/iscience/fulltext/S2589-0042(19)30352-9?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS2589004219303529%3Fshowall%3Dtrue (Accessed 06/11/19)
Qui, F. et al. (2017). Impacts of cigarette smoking on immune responsiveness: Up and down or upside down? Oncotarget. 8(1): 268–284. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5352117/ (Accessed 06/11/19)
Sellami, M. et al. (2018). Effects of Acute and Chronic Exercise on Immunological Parameters in the Elderly Aged: Can Physical Activity Counteract the Effects of Aging? Frontiers in Immunology. 9: 2187. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6191490/ (Accessed 06/11/19)
Simpson N, Dinges DF. (2007). Sleep and inflammation. Nutr. Rev. 65:S244–S252. Available at: https://www.ncbi.nlm.nih.gov/pubmed/18240557 (Accessed 06/11/19)
Stier, H. et al. (2014). Immune-modulatory effects of dietary Yeast Beta-1,3/1,6-D-glucan. Nutrition Journal. 13: 38. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4012169/ (Accessed 06/11/19)
Vetvicka, V. & Vetvickova, J. (2015). Glucan supplementation enhances the immune response against an influenza challenge in mice. Annals of Translational Medicine. 3(2): 22. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4322159/ (Accessed 06/11/19)
Wardle, A. & Cotton, D. (2014). Immune System Health. Lecture Notes. College of Naturopathic Medicine
Wu, D et al. (2019). Nutritional Modulation of Immune Function: Analysis of Evidence, Mechanisms, and Clinical Relevance. Nutritional Immunology. Available at: https://www.frontiersin.org/articles/10.3389/fimmu.2018.03160/full (Accessed 08/11/19)
Academy of Nutrition and Dietetics. (2017). Protect Your Health with Immune-Boosting Nutrition. Available at: https://www.eatright.org/health/wellness/preventing-illness/protect-your-health-with-immune-boosting-nutrition (Accessed 07/11/19)
Arnarson, A. (2017). 20 Foods That Are High in Vitamin E. Healthline. Available at: https://www.healthline.com/nutrition/foods-high-in-vitamin-e (Accessed 27/03/20)
Britannica Encyclopedia (2020). Humoral Immunity. Available at: https://www.britannica.com/science/humoral-immunity (Accessed 27/03/20)
Butler, N. (2018). 20 Foods Rich in Selenium. Healthline. Available at: https://www.healthline.com/nutrition/best-foods-high-in-zinc (Accessed 27/03/20)
Centers For Disease Control and Prevention. (2017). Medications that Weaken Your Immune System and Fungal Infections. Available at: https://www.cdc.gov/fungal/infections/immune-system.html (Accessed 06/11/19)
Gov.uk (2020). Major new measures to protect people at highest risk from coronavirus. Available at: https://www.gov.uk/government/news/major-new-measures-to-protect-people-at-highest-risk-from-coronavirus (Accessed 27/03/20)
Gov.uk (2020). Staying at home and away from others (social distancing). Available at: https://www.gov.uk/government/publications/full-guidance-on-staying-at-home-and-away-from-others/full-guidance-on-staying-at-home-and-away-from-others (Accessed 27/02/20)
Harvard Health Publishing (2019). How to Boost Your Immune System. Available at: https://www.health.harvard.edu/staying-healthy/how-to-boost-your-immune-system (Accessed 07/11/19)
Kerr, M. and Cafasso, J. (2017). Malabsorption Syndrome. Healthline. Available at: https://www.healthline.com/health/malabsorption (Accessed 28/03/20)
Kubala, J. (2018). Zinc: Everything You Need to Know. Healthline. Available at: https://www.healthline.com/nutrition/zinc (Accessed 05/11/19)
Link, R. (2020). 15 Healthy Foods That Are High in Folate (Folic Acid). Healthline. Available at: https://www.healthline.com/nutrition/foods-high-in-folate-folic-acid (Accessed 27/03/20)
Medline Plus (2019). Immune Response. Available at: https://medlineplus.gov/ency/article/000821.htm (Accessed 05/11/19)
Moliner, P. et al. (2010). Focus On: Alcohol and the Immune System. Alcohol Research Health. 33(1-2): 97–108. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3887500/ (Accessed 06/11/19)
Nall, R. (2018). What Causes Malabsorption? Medical News Today. Available at: https://www.medicalnewstoday.com/articles/322467.php (Accessed 08/11/19)
Nutri Advanced (2019). Health Notes. Immune Function. Available at: https://www.nutriadvanced.co.uk/healthnotes?resource=%2fassets%2fhealth-condition%2fimmune-function%2fhelpful-supplements (Accessed 06/11/19)
Nutri Advanced (2019). Health Notes. Quercetin. Available at: https://www.nutriadvanced.co.uk/healthnotes?resource=%2fassets%2fnutritional-supplement%2fquercetin%2f%7edefault (Accessed 06/11/19)
Perkins, S. (2018). How to Raise Your Vitamin D3 Level. SF Gate. Available at: https://healthyeating.sfgate.com/raise-vitamin-d3-level-3561.html (Accessed 27/03/20)
Riordon Clinic (2019). Seasonal Defense: Boosting Your Immune System. Available at: https://riordanclinic.org/2011/11/seasonal-defense-boosting-your-immune-system/ (Accessed 05/11/19)
Semeco, A. (2020). Top 12 Foods That Are High in Vitamin B12. Healthline. Available at: https://www.healthline.com/nutrition/vitamin-b12-foods (Accessed 27/03/20)
WebMD (2019). 16 Symptoms of Immune System Problems. Available at: https://www.webmd.com/cold-and-flu/immune-system-disorders#1 (Accessed 21/10/19)
WebMD (2020). What foods are rich in vitamin C? Available at: https://www.webmd.com/cold-and-flu/qa/what-foods-are-rich-in-vitamin-c (Accessed 27/03/20)
West, H. (2018). The 10 Best Foods That Are High in Zinc. Healthline. Available at: https://www.healthline.com/nutrition/best-foods-high-in-zinc (Accessed 27/03/20)
Windel, J. (unknown). Nutribullet: Natural Healing Foods. Supercharge your Health in just seconds a day! Nutribullet. Los Angeles, CA 90025. Pp. 37 and 41
World Health Organisation Europe (2019). Benefits of a Balanced Diet. Available at: http://www.euro.who.int/en/health-topics/disease-prevention/nutrition/a-healthy-lifestyle/benefits-of-a-balanced-diet (Accessed 07/11/19)
Zelman, K. (2019). The Benefits of Vitamin C. WebMD. Available at: https://www.webmd.com/diet/features/the-benefits-of-vitamin-c#1 (Accessed 05/11/19)