Immune Function

The immune system is the body’s defense system against irritants, toxins, infections, and the development of cancer. With an arsenal of “soldiers,” such as T-cells, B-cells, antibodies, macrophages, etc., the immune system can detect, attack, and remove potential dangers to optimal health. A nutrient-dense eating style with a variety of immune supporting phytochemicals is required to maintain an effective immune system.

  • Overview
  • Action Plan
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  • Success Stories


The goal of the immune system is to distinguish self from non-self. There are two main components to the immune system: the innate and the adaptive immune system. The innate immune system is made up of barriers in the form of skin and mucous membranes (of the mouth, nose, etc.) and chemical secreting cells that attract infection-fighting white blood cells. These cells kill foreign invaders by the process of “phagocytosis,” where the cell engulfs and destroys the invader. The adaptive immune system is made of B cells, which secrete antibodies against invaders, and T cells, which help destroy infected cells. These two systems work together to optimize health utilizing numerous chemical messengers, like interferon, interleukins, and the complement system. Dysfunction in one “soldier” can have dangerous systemic effects throughout the whole body.

Impaired immune systems lead to frequent viral, bacterial or fungal infections, as well as an increased risk of cancer. When the immune system fails and recognizes “self” as “non-self,” autoimmune disease can occur where the immune system attacks a person’s own tissues. For example, Hashimoto’s thyroiditis occurs when the immune system attacks the thyroid gland. Rheumatoid arthritis occurs when the immune system attacks joints.

Many factors can cause dysfunction in the body’s defense system, including nutritional, psychological, environmental, and hormonal factors. Nutrition has the largest impact on the immune system. The Standard American Diet with its low-nutrient, highly processed refined carbohydrates; trans, saturated, and processed fats; and large amounts of animal products sets the stage for an impaired immune system. An assortment of natural plant foods is needed to support optimal immune function. Nutrient deficiencies, excess sugar consumption, and food sensitivities can further depress the immune system.1 Negative emotional states (e.g. depression) and stressors (e.g. the loss of a spouse) were found to decrease the body’s ability to fight infection and may increase risk of allergies or autoimmune diseases.2 Sleep deprivation, alcohol abuse, and smoking also impair immunity.

  1. Chandra RK. Impact of nutritional status and nutrient supplements on immune responses and incidence of infection in older individuals. Ageing Res Rev 2004, 3:91-104.
  2. Segerstrom SC, Miller GE. Psychological stress and the human immune system: a meta-analytic study of 30 years of inquiry. Psychol Bull 2004, 130:601-630.

Action Plan


  • A Nutritarian diet provides an array of vitamins, minerals, and antioxidants that contribute to a robust immune system capable of defending against infections and cancer, and protecting against autoimmunity. The antioxidant and anti-inflammatory actions of vitamins, minerals and phytochemicals help to prevent excessive oxidative stress and inflammation, and many nutrients and phytochemicals promote proper immune cell function.1
  • Whole plant foods provide adequate vitamins C and E, carotenoids, flavonoids, folate, and various antioxidants and phytochemicals with immune-modulating functions. For example, cruciferous vegetables promote intestinal immune function. Mushrooms contain immune-supporting beta-glucans. Beans and other legumes provide fiber and resistant starch to nourish the microbiome. Berries are rich in flavonoids, which have anti-inflammatory effects.1-7


  • Dr. Fuhrman’s general supplement protocol for adults (see Vitamin Advisor for details) includes:
  • Additional notes:
    • Ensure adequate Vitamin D levels by having your physician check serum 25(OH)D levels. Vitamin D enhances the immune system by up-regulating clearance of bacteria by immune cells and increasing T cell activation. Vitamin D supplementation has been found to decrease the frequency of viral upper respiratory infections.8
    • Zinc is essential for immune function and absorption of zinc is lower from plant foods than animal foods. Zinc supplementation as part of a multivitamin and mineral supplement is important for many who follow plant-based diets.9,10


  • Exercise is an effective stress-reducing activity that also enhances immunity. Research suggests regular exercise boosts immunity, leading to fewer and less severe respiratory illnesses.11


  • Adequate restful sleep each night is essential for a healthy immune system. Sleep deprivation has been found to adversely affect immunity.12

Other considerations 

  • Chronic stress suppresses immune function and is linked to greater susceptibility to upper respiratory infections.13,14 Meditation could help reduce stress and improve a person’s emotional state, leading to a stronger immune system.
  • Alcohol, especially regular heavy drinking, suppresses immune system function. Alcohol cessation is essential to optimal immunity.15


Find additional help

ONLINE: All members of can search the Ask the Doctor archives for discussions on this topic. Platinum and Diamond members can connect with Dr. Fuhrman by posting questions in the forum. Not a member? Join now.

IN PERSON: Book a stay at Dr. Fuhrman’s Eat to Live Retreat in San Diego, California. With options ranging from one, two and three months (and sometimes longer) you will be under Dr. Fuhrman’s direct medical supervision as you hit the “reset” button on your health. For more information: (949) 432-6295 or [email protected]

EVENTS: Join Dr. Fuhrman for an online boot camp, detox or other event. During these immersive online events, you’ll attend zoom lectures, follow a special meal plan, and have access to a special, live Q&A session with Dr. Fuhrman. Learn more about events.

  1. Linus Pauling Institute Micronutrient Information Center. Immunity in Depth []
  2. Yahfoufi N, Alsadi N, Jambi M, Matar C. The Immunomodulatory and Anti-Inflammatory Role of Polyphenols. Nutrients 2018, 10. doi: 10.3390/nu10111618
  3. Jeong SC, Koyyalamudi SR, Pang G. Dietary intake of Agaricus bisporus white button mushroom accelerates salivary immunoglobulin A secretion in healthy volunteers. Nutrition 2012, 28:527-531. doi: 10.1016/j.nut.2011.08.005
  4. Dai X, Stanilka JM, Rowe CA, et al. Consuming Lentinula edodes (Shiitake) Mushrooms Daily Improves Human Immunity: A Randomized Dietary Intervention in Healthy Young Adults. J Am Coll Nutr 2015, 34:478-487. doi: 10.1080/07315724.2014.950391
  5. Hooper LV. You AhR what you eat: linking diet and immunity. Cell 2011, 147:489-491. doi: 10.1016/j.cell.2011.10.004
  6. Naithani R, Huma LC, Holland LE, et al. Antiviral activity of phytochemicals: a comprehensive review. Mini Rev Med Chem 2008, 8:1106-1133. doi:
  7. Sonnenburg ED, Sonnenburg JL. Starving our microbial self: the deleterious consequences of a diet deficient in microbiota-accessible carbohydrates. Cell Metab 2014, 20:779-786. doi: 10.1016/j.cmet.2014.07.003
  8. Martineau AR, Jolliffe DA, Greenberg L, et al. Vitamin D supplementation to prevent acute respiratory infections: individual participant data meta-analysis. Health Technol Assess 2019, 23:1-44. doi: 10.3310/hta23020
  9. Prasad AS. Zinc in human health: effect of zinc on immune cells. Molecular Medicine 2008, 14:353-357. doi: 10.2119/2008-00033.Prasad
  10. Foster M, Chu A, Petocz P, Samman S. Effect of vegetarian diets on zinc status: a systematic review and meta-analysis of studies in humans. J Sci Food Agric 2013, 93:2362-2371. doi: 10.1002/jsfa.6179
  11. Nieman DC, Henson DA, Austin MD, Sha W. Upper respiratory tract infection is reduced in physically fit and active adults. Br J Sports Med 2011, 45:987-992. doi: 10.1136/bjsm.2010.077875
  12. Irwin MR. Why sleep is important for health: a psychoneuroimmunology perspective. Annu Rev Psychol 2015, 66:143-172. doi: 10.1146/annurev-psych-010213-115205
  13. Vitlic A, Lord JM, Phillips AC. Stress, ageing and their influence on functional, cellular and molecular aspects of the immune system. Age (Dordr) 2014, 36:9631. doi: 10.1007/s11357-014-9631-6
  14. Pedersen A, Zachariae R, Bovbjerg DH. Influence of psychological stress on upper respiratory infection--a meta-analysis of prospective studies. Psychosom Med 2010, 72:823-832. doi: 10.1097/PSY.0b013e3181f1d003
  15. Pasala S, Barr T, Messaoudi I. Impact of Alcohol Abuse on the Adaptive Immune System. Alcohol Res 2015, 37:185-197. 

Ask The Doctor

The following are sample questions from the Ask the Doctor Community Platinum and higher members can post their health questions directly to Dr. Fuhrman. (All members can browse questions and answers.)


Do you have a supplement formulated to specifically to enhance protection against cancer?


Dietary supplements by definition do not treat, prevent, or cure a disease and cannot claim to on labels or in advertising. However, plant extracts are continually being studied for their potential to maintain health and affect the disease process.  Clinical trials are being conducted, aiming to figure out whether certain plant extracts could affect cancer-related biomarkers, act as beneficial adjunct treatments to be used with chemotherapy, or help to prevent progression of an early stage cancer or pre-cancerous condition. Read more


Are there any good foods/supplements/herbs that will lighten the symptoms or shorten the duration of a cold once its symptoms present and the ‘normal process’ begins?


There is considerable science to suspect that if an herbal product could relieve cold symptoms, then it should be avoided due to toxicity. You can’t have it both ways; if it works, it has pharmacologic properties and that means it is toxic, and if it is not toxic, it cannot work. The symptoms of the cold are the remedy, they occur to remove and defend against the viral attack. Excellent nutrition gives us better immunity, which means your defenses are heightened and your ability to respond to illness is quicker and more complete. If you are eating and supplementing properly when well, you are already at maximum function. If you could take something to improve immune function, it should be used regularly, not just when sick because once you are sick, you can’t suddenly get great nutrition, that only occurs from months of eating properly.


Recently, my immune system seems to be very weak. I have had various infections over the last three months. My diet is 80% Nutritarian (plus fish oil and vitamin D every day). I have to admit that I am not too physically active, and I love sweets; I have dessert almost every other day.

Is there anything specific I can do to boost my immune function?


You probably know what I’m going to say – if you’re having SAD desserts with sugar, trans fats, and high fructose corn syrup or other sweeteners, this really will impact your immune function over time. When you can make a commitment to 90-100 percent Nutritarian diet, you’ll see that the frequency of infections will diminish tremendously. I highly recommend that you read Super Immunity. Try some of my delicious healthy desert recipes that are helpful to break your addiction to overly sweetened conventional deserts. Plus, maybe you are one of those people who require more zinc, and maybe you need more B12 too. It might be helpful to take my multivitamin to fill in these deficiencies in your diet.


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