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
  • Ask The Doctor
  • Related Info
  • 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 auto-immunity. This type of eating style provides adequate Vitamin C, E, carotenes, folate, and various antioxidants and phytochemicals. A Nutritarian diet also contains seeds and nuts supplying fat in a form that maximizes absorption of micronutrients from other foods consumed in the same meal. Eating a whole food, plant-based, nutrient dense diet has more benefits than obtaining micronutrients through supplement form; however, the conservative use of supplements to assure nutritional completeness of one’s diet can be helpful, especially if following a vegan diet without ideal levels of zinc, B12, Vitamin D, iodine or DHA.
  • The foods with scientifically documented immune-system benefits that have been shown to significantly reduce risk of cancer (as well as other benefits) include cruciferous greens, beans, onions, mushrooms, berries, and seeds. (G-BOMBS).
  • Ensure adequate Vitamin D supplementation by having your physician check serum 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.1
  • Alcoholics have depressed immune systems that increase susceptibility to infections. Alcohol cessation is essential to optimal immunity.

Stress relief

  • Meditation and hypnosis improve the emotional state of a person, leading to a stronger immune system.
  • Exercise is an effective stress-release technique that also enhances immunity.

Sleep hygiene

Adequate restful sleep each night is essential for a healthy immune system. Sleep deprivation has been found to adversely affect immunity.2

Other considerations

For more complete information and an action plan for immune system protection and repair, please see my book, Super Immunity.

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  1. Aranow C. Vitamin D and the immune system. J Investig Med 2011, 59:881-886.
  2. Irwin MR. Why Sleep Is Important for Health: A Psychoneuroimmunology Perspective. Annu Rev Psychol 2014.

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.