What are the most effective natural strategies to boost immune function?

Natural Immune Support Strategies

The most effective natural immune boosters are vitamin D supplementation (2000 IU/day), adequate protein intake (≥1.2 g/kg/day), consuming at least five portions of fruits and vegetables daily, and daily probiotic supplementation with Lactobacillus and Bifidobacterium species. 1

Primary Evidence-Based Interventions

Vitamin D Supplementation

• Vitamin D at 2000 IU/day has the strongest evidence for reducing respiratory infection risk, particularly during autumn and winter months when infection risk is highest. 1
• Players deficient or insufficient in vitamin D benefit from vitamin D3 supplementation to optimize immune defense against the common cold. 1
• Vitamin D is essential for absorption of calcium and necessary for healthy bones and a healthy immune system. 2
• Adequate vitamin D status is critical because deficiency decreases immune defenses against invading pathogens and makes individuals more susceptible to infection. 1

Adequate Protein Intake

• Protein intakes of at least 1.2 g/kg body weight per day are required for optimal immune function. 1
• In cases of overreaching or high physical stress, even higher intakes (up to 3 g/kg/day) can reduce the incidence of respiratory infection. 1
• Inadequate protein-energy intake decreases immune defenses and increases infection susceptibility. 1

Fruit and Vegetable Consumption

• Consume at least five portions of fresh fruit and vegetables per day on at least 5 days per week. 1
• High intakes of fresh fruit and vegetables are associated with reduced infection risk in highly physically active people. 1
• This dietary pattern ensures adequate intake of essential micronutrients (vitamins A, C, E, B vitamins, and minerals) that support immune health. 1

Probiotic Supplementation

• Daily probiotic ingestion with Lactobacillus and Bifidobacterium species results in fewer days of respiratory illness and lower severity of illness symptoms. 1
• A meta-analysis of 12 studies involving both athletic and non-athletic populations supports reduced incidence of respiratory illness. 1
• Probiotics may also reduce the severity and/or duration of gastrointestinal illness. 1

Essential Micronutrients for Immune Function

Critical Micronutrients to Maintain

• Deficiencies in iron, zinc, magnesium, manganese, selenium, copper, vitamins A, C, D, E, B6, B12, and folic acid decrease immune defenses. 1
• A broad-range multivitamin/mineral supplement is the best choice to support food intake when food choices and quality may be limited. 1
• Adequate levels of essential nutrients are important to support immune health throughout the season. 1

Zinc Supplementation

• Taking 75 mg/day of zinc lozenges when symptoms of a cold begin reduces the duration of symptoms. 1
• Zinc supplementation should only be used when plasma zinc levels are documented as low (<0.75 mmol/L). 3
• High zinc intake (≥30 mg daily) can induce copper deficiency, leading to neutropenia, anemia, and paradoxically reduced immune function. 3

Vitamin C

• Vitamin C plays an important role in immune function, particularly in older adults who are vulnerable to infections due to reduced immune function. 1
• Correcting documented vitamin C deficiency decreases immune defenses and infection susceptibility. 3
• Adequate vitamin C can be obtained through dietary sources including citrus fruits and vegetables. 1

Additional Beneficial Interventions

Polyphenol-Rich Beverages

• Daily consumption of polyphenol supplements or beverages (non-alcoholic beer, green tea) is associated with reduced respiratory infection risk. 1
• Several studies in athletes indicate consistent benefits from these plant-derived compounds. 1

Vitamin E (Age-Specific)

• For adults over 60 years old, vitamin E at 200 IU/day improves T cell-mediated immune function. 1
• This dose is most effective in improving age-associated immune dysfunction, outperforming both 60 IU/day and 800 IU/day doses. 1
• Vitamin E supplementation enhances antibody titers to vaccines and delayed-type hypersensitivity response in older adults. 1

Lifestyle Factors That Support Immunity

Energy Availability and Carbohydrate Intake

• Low energy availability is associated with increased risk of illness. 1
• Restricting carbohydrates (e.g., 'training low') may increase immunosuppressive stress hormone responses. 1
• Maintain adequate energy intake to support robust immunity. 1

Sleep and Recovery

• Ensuring adequate recovery and sleep is just as important as nutritional strategies in reducing infection risk. 1
• Effects on eating and sleeping can affect training ability, performance, and recovery. 1

Alcohol Limitation

• Limit alcohol intake to no more than 2 units per day and avoid binge drinking, which negatively impacts immune cell functioning. 1

Hygiene and Stress Management

• Good personal, home, and training venue hygiene are important considerations alongside nutrition. 1
• Psychological stress management helps reduce infection risk. 1
• Managing training and competition load prevents overreaching and overtraining that can compromise immunity. 1

Dietary Pattern Approach

Mediterranean Diet Benefits

• The Mediterranean diet, which prioritizes whole grains, fruits, vegetables, and healthy fats, has been linked to reduced levels of inflammation and lower chance of developing chronic diseases. 1
• This eating pattern supports gut microbiota health, which substantially impacts immune system functioning. 1

Avoid Western Diet Pattern

• The Western diet, high in processed foods, red and processed meat, and refined carbohydrates, has been associated with elevated inflammation and impaired immune function. 1
• Diets high in saturated and trans fats may promote inflammation and decrease immune system function. 1

Important Clinical Caveats

When NOT to Supplement

• Currently, there is insufficient evidence to justify the use of supplements beyond those mentioned above to boost immunity and/or reduce infection incidence. 1
• No established evidence supports routine empirical use of supraphysiologic doses of vitamin C or zinc to prevent or improve outcomes in viral infections. 3

Populations at Higher Risk

• Illness-prone individuals should implement nutritional measures throughout the season or at least during autumn and winter months. 1
• Periods of fixture congestion or high stress increase infection risk and warrant closer attention to nutrition. 1
• Older adults are particularly vulnerable to infections due to reduced immune function and may benefit from targeted supplementation. 1

Foundation First

• Ensure adequate dietary intake through whole foods before considering supplementation. 1
• Consider supplementation as part of a broader nutritional strategy including adequate protein and other micronutrients. 4
• A balanced diet with variety of fruits and vegetables helps ensure adequate intake of essential nutrients with little risk of excess. 5