Introduction

Supporting the immune system is essential for maintaining overall health. Deficiencies in key vitamins and minerals—including vitamin C and zinc—have been shown to impair immune responses and increase vulnerability to illness. (Tourkochristou 2021) Other ingredients like astragalus and probiotics have also demonstrated potential in supporting immune resilience. (Li 2022)(Mazziotta 2023)

There is a growing interest in using supplements to strengthen immunity. (Crawford 2022) The ingredients selected for this protocol form the basis of a targeted approach to general immune support aimed at enhancing physiological defenses.

Ingredients

Astragalus (Astragalus membranaceus)

Dosing: 500–2,000 mg standardized extract daily, taken in divided doses for up to 2–3 months (Tang 2009)(Zou 2013)(Ny 2021) 

Supporting evidence:

• In preclinical and clinical studies, astragalus polysaccharides have demonstrated immunomodulatory effects to support both innate and adaptive immune responses. Specifically, they may increase phagocytic and natural killer (NK) cell activity and support antibody production. (Chen 2020)(Li 2022)  
• One review explored the effects of astragalus on upper respiratory tract infection (URTI) in children with nephrotic syndrome (n=130). Children, aged 1.5–14 years, who were coadministered astragalus granules with prednisone for at least three months had a significantly reduced incidence of URTI compared to those who received prednisone monotherapy. (Zou 2013)
• Astragalus’ immunosupportive properties have been studied specifically in relation to hepatitis B virus (HBV). In a clinical trial involving 208 Chinese patients (age range 25–56 years) with chronic HBV, treatment with an astragalus-based compound led to significantly greater rates of symptom resolution and recovery of liver function (65.5%) compared to the control group receiving drugs in regular clinical use in traditional Chinese medicine (TCM) for viral hepatitis—silibinin, oleanolic acid, and Yiganling (28.3%). (Tang 2009) A separate study concluded that astragalus polysaccharides act as a potent adjuvant to the hepatitis B subunit vaccine, enhancing both humoral and cellular immune responses. (Du 2011)

Probiotics

Dosing: Variable depending on formulation and patient age 

Supporting evidence:

• Probiotics support the immune system by modulating gut microbiota composition, enhancing gut barrier function, and interacting with immune cells to regulate inflammatory responses. (Yan 2011) 
• A Cochrane review including 23 individual randomized controlled trials (RCTs) and one cluster RCT found that probiotics likely reduce the risk of experiencing at least one episode of acute URTI and may reduce the mean duration of URTI episodes by about 1.2 days. Probiotics also likely reduce the use of antibiotics for treating URTIs. The most common probiotic doses used in the included studies were between 1–100 billion colony-forming units (CFU) per day for more than three months. (Zhao 2022)
• A double-blind, placebo-controlled RCT evaluated the effects of probiotic supplementation on the incidence and duration of cold and influenza-like symptoms in healthy children aged 3–5 years (n=326) over a six-month winter period. Children received twice-daily placebo, Lactobacillus acidophilus NCFM, or L. acidophilus NCFM plus Bifidobacterium animalis subsp. lactis Bi-07. Both probiotic groups showed significant reductions in the incidence and duration of fever (53% and 72.7%), cough (41.4% and 62.1%), and rhinorrhea (28.2% and 58.5%) compared with placebo, along with fewer antibiotic prescriptions and childcare absences. (Leyer 2009)
• In a double-blind, placebo-controlled RCT with 65 healthy adults aged 18–44 years, a dietary supplement containing L. plantarum PBS067, L. acidophilus PBS066, and B. lactis BL050 more effectively alleviated and reduced the duration of cold symptoms (i.e., fever, muscle pain) and reduced pro-inflammatory cytokine levels over a six-week treatment period. (Lungaro 2025)
• Research suggests that certain Lactobacillus strains can act as adjuvants to influenza vaccination. In animal models and humans, oral or nasal supplementation with Bifidobacteria and Lactobacilli before and after vaccination has been shown to enhance systemic and mucosal immune responses, increasing vaccine-specific IgG and secretory IgA production, improving seroconversion rates, and modulating T helper cell activity and cytokine balance. (Davidson 2011)(Rizzardini 2012)(Jung 2020)(Tonetti 2020)

Vitamin C

Dosing: 250–1,000 mg daily, ongoing (Hemilä 2013) 

Supporting evidence:

• Vitamin C supports immune function by maintaining the integrity of the epithelial barrier, a critical first line of defense against pathogen entry into the body. It also enhances the proliferation, differentiation, and activity of immune cells, including neutrophils, B cells, and T cells, thereby improving the efficiency of pathogen killing and clearance. (Carr 2017)
• Vitamin C is a potent antioxidant that scavenges reactive oxygen species (ROS) and reduces inflammation. (Gęgotek 2022) Weak antioxidant defenses can weaken the immune system and increase susceptibility to illness and disease. (Khadim 2021) 
• Research suggests that ongoing vitamin C supplementation may reduce the risk of the common cold. A subgroup analysis from a Cochrane review found that regular supplementation reduced incidence by 50% in individuals under high physical stress, such as marathon runners, skiers, and soldiers (n=598). In other studies, vitamin C was associated with an 8% reduction in adults and an 18% reduction in children. (Hemilä 2013)

Vitamin D

Dosing: 

• Loading dose (to correct deficiency): 50,000 IU once weekly for 2–3 months (Kennel 2010)
• Maintenance dose: 300–4,000 IU daily, ongoing (Martineau 2017) 

Supporting evidence:

• The vitamin D receptor is expressed on immune cells, enabling vitamin D to enhance the pathogen-fighting activity of innate immune cells, modulate adaptive immune pathways, and stimulate the production of antimicrobial peptides like cathelicidin. (Aranow 2011)(Wei 2015) 
• Vitamin D deficiency is associated with increased susceptibility to infection. (Aranow 2011)
• According to this study, short-term repletion of vitamin D in elderly adults with deficiency before receiving an influenza vaccine shifts immune signaling toward a less inflammatory, more tolerogenic profile (lower tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL‑6), higher transforming growth factor beta (TGF-β)) one month after vaccination. (Goncalves-Mendes 2019)
• In a prospective, double-blind, placebo-controlled RCT conducted in Japanese schoolchildren (n=334), daily cholecalciferol during winter reduced laboratory-confirmed influenza A from 18.6% to 10.8% (relative risk 0.58), which corresponds to a 42% relative risk reduction in incidence. (Urashima 2010)

Zinc

Dosing: 75–276 mg daily as zinc gluconate or zinc acetate for up to 21 days (Hemilä 2011) (Nault 2024)

Supporting evidence:

• Zinc insufficiency impairs the production and activation of T cells, leading to an increased risk of infectious diseases like pneumonia. (Walker 2004)(Hönscheid 2009) 
• Zinc may help prevent respiratory infections by enhancing interferon-alpha–mediated antiviral responses, inhibiting viral replication, reducing angiotensin-converting enzyme 2 (ACE2) receptor activity relevant to SARS-CoV-2, supporting mucociliary clearance of pathogens from the respiratory tract, and exerting direct antibacterial effects. (Skalny 2020)
• A meta-analysis of three RCTs, including a total of 199 patients, concluded that zinc acetate lozenges reduced the duration of the common cold by almost three days. (Hemilä 2016)
• According to a Cochrane review, including six studies that involved 5,193 children aged 2–59 months, zinc supplementation reduced the incidence and prevalence of pneumonia by 13% and 41%, respectively. (Lassi 2016)