Leafy Greens For The Immune System

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Introduction

The immune system is an essential part of protecting our body from foreign pathogens, substances, germs and cell changes.  The immune system can be triggered by antigens, which are foreign substances that are not recognised by the immune system. Thus, it elicits a response. Having a balanced diet that incorporates leafy greens can protect you from various diseases, such as diabetes and cardiac diseases. The purpose of this article is to provide information on the nutritional value of leafy greens and how they affect the immune system. There are also recipe ideas on how to incorporate them into your diet.

Nutritional value of leafy greens

Several leafy greens are high in minerals, vitamins and fibre.  The main components found in leafy greens are vitamins A, K, E, and C, folate, and beta-carotene as well as the vitamins B1, B2, B2, B5 and B6.

Kale is considered a superfood due to its nutrient-rich components that are still being investigated for its benefits. Currently, we know that kale is from the family Brassicaceae. Most people have kale raw. Klae consists of vitamins A, C, K and folate as well as magnesium, potassium and calcium.1

Cabbage is also part of the Brassicaceae family, which grows in more than 90 countries. It has several health benefits, including reducing the risk of heart disease, Alzheimer’s, cancer, and diabetes.  It is rich in calcium, vitamin C, and E. Cabbage has been incorporated into traditional medicine for years to treat diseases such as gastritis and irritable bowel syndrome (IBS).2 A study has shown that cabbage can protect you from oxidative stress. As oxidative stress plays a significant role in the development of cardiac disease,  the benefits of cabbage seem to go against this. 

Spinach also contains essential nutrients such as vitamin A, iron and potassium. It is suggested that it may prevent constipation, lower blood pressure, and assist in asthma management. 

Broccoli is another nutritional leafy green that provides several health benefits for the immune system. Within this category, it also includes cauliflower, bok choy and cabbage. Bok Choy contains isothiocyanate sulforaphane (SULF). SULF is currently gaining the attention of researchers, as studies have suggested that it has mechanisms to block mutation in DNA that would normally result in cancer.3 To further add on, it has been demonstrated to reduce immune cell proliferation.4

Other leafy greens that are rich in nutrients include: 

  • Arugula
  • Mustard greens
  • Brussels sprouts
  • Beet greens
  • Watercress
  • Collard greens 
  • Savoy cabbage

Antioxidants 

Antioxidants are found in food and play a role in protecting the body from free radicals. Research has suggested that plant-based diets with a high amount of leafy greens could protect you from type 2 diabetes, cardiovascular disease (CVD) and even cancer.5 Antioxidants like beta-carotene (B-carotene), lutein, and vitamin E can function to prevent several cardiovascular diseases. As the role of antioxidants is to fight free radicals, they can decrease the oxidative stress of cells. B-carotene through antioxidant function may protect you from cancer as it has anticarcinogenic properties.6

Vitamin E is a nutrient known to be most effective in regulating the immune system. Its ability to directly and indirectly aid immune cells has been studied. Immune cells contain high amounts of vitamin E, to protect their membrane of polyunsaturated fat against oxidative damage. Furthermore, vitamin E may be involved in the activation of signalling molecules and the integrity of the membrane.7

Additionally, vitamin C is another antioxidant that can protect cells from reactive oxygen species (ROS) during an immune response.  Leukocytes and neutrophils can transport vitamin C in its oxidised form to function as a defence mechanism for the immune system. Vitamin C is not only found in leafy greens but also in potatoes and citrus. Neutrophils and monocytes can accumulate 100 times more vitamin C than plasma, indicating the importance of vitamin C for immune functions. A research study by Bozonet et al. has demonstrated that there was a 20% increase in the chemotactic activity of neutrophils, suggesting that vitamin C plays a role in innate immunity.8 The leafy greens that have a high vitamin C content are broccoli, kale and snow peas.

Vitamin A is considered an anti-inflammation vitamin as it is involved in the cellular immune response as well as the humoral immune response. A mice study demonstrated that vitamin A deficiency resulted in the lack of T-cell response and inhibition of normal apoptosis in bone marrow cells. This illustrated that vitamin A is vital in the regulation of homeostasis of bone marrow.9 B-carotene is a provitamin A that is used to prevent vitamin A deficiency. It is also found in leafy greens. It can convert to retinol, which is the active form of vitamin A. The role of  B-carotene can boost immunity as studies have shown that B-carotene can increase T-cell levels after seven days.10

Other nutrients

Folate is found in a lot of leafy greens, which are water-soluble vitamins B9. It can also be added to foods and sold as supplements, known as folic acid.11 The Recommended Dietary Allowance (RDA) has stated that men and women over the age of 19 should strive for 400 micrograms (mcg) of dietary folate equivalents (DFE) whilst pregnant women should take 500-600 mc DFE.11 folate is prominently found in spinach, asparagus, brussels sprouts, turnip greens and broccoli. 

Furthermore, calcium has a role in the immune system. It can activate cells and act as a secondary messenger in various cell types.12,13 Vegetables high in calcium are kale, collard greens, and bok choy. Broccoli and beet greens.  It is recommended that those over the age of 19 should take 1000 mg (milligrams) for both males and females.14

Overall, nutrition is important in supporting the immune system, as a high-nutrient diet ensures:15

  • The functioning of the immune system.
  • Regulates metabolism
  • Ensures new generation of cells and protein production for antibodies
  • Protection from inflammatory and oxidative stress

Immune system - function

The role of the immune system is to protect you from foreign pathogens and toxins. The immune system consists of two specific defence systems which are known as the ‘two arms of the immune system’: the innate and adaptive system. The innate immune system consists of non-specific macrophages and phagocytes. The innate immune system can develop rapidly if a foreign pathogen enters your body. The cells respond to the pathogens in a non-specific way. The adaptive immune system consists of T-lymphocytes and B-lymphocytes, which are specific responses to a certain pathogen. T-lymphocytes are commonly known as T cells, which are produced in the bone marrow and then relocated to the thymus. They use chemical messengers to send signals to cells in the immune system, and they can also destroy foreign pathogens using toxins. As it is a specific response, the adaptive response takes slower to develop, unlike the innate immune system. However, it is much more effective against pathogens and provides a faster response when exposed to the same pathogen due to memory B-cells.16 Several factors can weaken the immune system:

Recipes and meal ideas

There are several ways to incorporate leafy greens into meals. Some people may dislike the taste of some vegetables; therefore, these are some links to some creative and simple dishes:

  1. https://www.delicious.com.au/recipes/collections/gallery/22-ways-to-cook-with-leafy-greens/ghx3iiyh?page=8
  2. https://thehealthyepicurean.com/ways-to-eat-more-leafy-greens/
  3. https://goop.com/food/recipes/dark-leafy-green-recipes/ 
  4. https://www.bbcgoodfood.com/recipes/collection/green-smoothie-recipes 

Summary

Overall, there are many health benefits of leafy greens for the immune system and overall health. It is important to incorporate them into your diet to have a strong immune system, as several factors can weaken the immune system, including stress, lack of sleep, poor diet and age.  There are several ways to include leafy greens in your diet, whether as a snack, meal or even a smoothie.  In conclusion, this article provides a comprehensive understanding of the relationship between leafy greens and the immune system by emphasising the importance of incorporating them into a balanced diet for a healthy immune system.

References

  1. Alfawaz HA, Wani K, Alrakayan H, Alnaami AM, Al-Daghri NM. Awareness, knowledge and attitude towards ‘superfood’ kale and its health benefits among arab adults. Nutrients [Internet]. 2022 Jan 7 [cited 2023 Nov 4];14(2):245. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8782012/
  2. Yang DK. Cabbage (Brassica oleracea var. capitata) protects against h2o2-induced oxidative stress by preventing mitochondrial dysfunction in h9c2 cardiomyoblasts. Evid Based Complement Alternat Med [Internet]. 2018 Aug 12 [cited 2023 Nov 4];2018:2179021. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6109504/
  3. Vanduchova A, Anzenbacher P, Anzenbacherova E. Isothiocyanate from broccoli, sulforaphane, and its properties. J Med Food. 2019 Feb;22(2):121–6. 
  4. Totsch SK, Waite ME, Sorge RE. Chapter fifteen - dietary influence on pain via the immune system. In: Price TJ, Dussor G, editors. Progress in Molecular Biology and Translational Science [Internet]. Academic Press; 2015 [cited 2023 Nov 4]. p. 435–69. (Molecular and Cell Biology of Pain; vol. 131). Available from: https://www.sciencedirect.com/science/article/pii/S1877117314000283
  5. Stanner S, Weichselbaum E. Antioxidants. In: Caballero B, editor. Encyclopedia of Human Nutrition (Third Edition) [Internet]. Waltham: Academic Press; 2013 [cited 2023 Nov 4]. p. 88–99. Available from: https://www.sciencedirect.com/science/article/pii/B9780123750839000131
  6. Lobo V, Patil A, Phatak A, Chandra N. Free radicals, antioxidants and functional foods: Impact on human health. Pharmacogn Rev [Internet]. 2010 [cited 2023 Nov 4];4(8):118–26. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3249911/
  7. Lewis ED, Meydani SN, Wu D. Regulatory role of vitamin E in the immune system and inflammation. IUBMB Life [Internet]. 2019 Apr [cited 2023 Nov 4];71(4):487–94. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7011499/
  8. Moore A, Khanna D. The role of vitamin c in human immunity and its treatment potential against covid-19: a review article. Cureus [Internet]. [cited 2023 Nov 4];15(1):e33740. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9925039/
  9. Huang Z, Liu Y, Qi G, Brand D, Zheng SG. Role of vitamin a in the immune system. J Clin Med [Internet]. 2018 Sep 6 [cited 2023 Nov 4];7(9):258. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6162863/
  10. Clark S. Beta carotene. In: Enna SJ, Bylund DB, editors. xPharm: The Comprehensive Pharmacology Reference [Internet]. New York: Elsevier; 2007 [cited 2023 Nov 4]. p. 1–3. Available from: https://www.sciencedirect.com/science/article/pii/B9780080552323613029
  11. Office of dietary supplements - folate [Internet]. [cited 2023 Nov 4]. Available from: https://ods.od.nih.gov/factsheets/Folate-HealthProfessional/
  12. Vig M, Kinet JP. Calcium signaling in immune cells. Nat Immunol [Internet]. 2009 Jan [cited 2023 Nov 4];10(1):21–7. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2877033/
  13. Grinstein S, Klip A. Calcium homeostasis and the activation of calcium channels in cells of the immune system. Bull N Y Acad Med [Internet]. 1989 Jan [cited 2023 Nov 4];65(1):69–79. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1807782/
  14. Office of dietary supplements - calcium [Internet]. [cited 2023 Nov 4]. Available from: https://ods.od.nih.gov/factsheets/Calcium-HealthProfessional/
  15. Calder PC. Nutrition and immunity: lessons for COVID-19. Eur J Clin Nutr [Internet]. 2021 Sep [cited 2023 Nov 4];75(9):1309–18. Available from: https://www.nature.com/articles/s41430-021-00949-8
  16. The innate and adaptive immune systems. In: InformedHealth.org [Internet] [Internet]. Institute for Quality and Efficiency in Health Care (IQWiG); 2020 [cited 2023 Nov 4]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK279396/

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Maysaah Seif Suleiman

Bachelors of Science Microbiology, BSc Microbiology, University of Reading

I am a recent Microbiology graduate. I have had the opportunity to contribute to two research projects during my time as an undergraduate; in vitro lung models to assess antimicrobial drug activities and discover a potential diagnostic tool for Mycobacterium bovis.

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