What vitamins should be taken to prevent routine viral infections?

From the Guidelines

Vitamin D, vitamin A, and zinc are the most critical nutrients for preventing routine viral infections, with vitamin D supporting immune function, vitamin A acting as an anti-infective vitamin, and zinc inhibiting viral replication and supporting immune cell function. For vitamin D, a daily supplement of 1000-2000 IU is recommended for most adults, with some individuals potentially benefiting from higher doses (up to 4000 IU daily) under healthcare supervision 1. Vitamin A has been defined as an “anti-infective” vitamin, and its deficiency is involved in various infectious diseases, including measles and diarrhea 1. Zinc is also beneficial, with 15-30 mg daily during cold and flu season being helpful, as it helps inhibit viral replication and supports immune cell function 1. Additionally, ensuring adequate intake of other essential nutrients such as vitamins C, E, B6, and B12, as well as selenium, iron, and omega-3 polyunsaturated fatty acids, is important for maintaining robust immunity 1. These supplements work best when combined with adequate sleep (7-9 hours nightly), regular exercise, proper hydration, and a balanced diet rich in fruits and vegetables. While these vitamins can support immune function, they are not guaranteed protection against all viral infections and should complement good hygiene practices like handwashing. It is essential to note that there is no established evidence that routine, empirical use of supraphysiologic or supratherapeutic amounts of micronutrients may prevent or improve clinical outcomes of viral infections, and therefore, daily allowances for vitamins and trace elements should be ensured to malnourished patients at risk for or with viral infections 1.

Some key points to consider:

• Vitamin D status is crucial in optimizing immune defense against the common cold, and players who are deficient or insufficient in vitamin D are likely to benefit from vitamin D3 supplementation (2000 IU/day) 1.
• High intakes of fresh fruit and vegetables are associated with reduced infection risk in highly physically active people, and footballers should follow the standard recommendation of at least five portions of fruit and vegetables per day on at least 5 days per week 1.
• Daily probiotic ingestion may result in fewer days of respiratory illness and lower severity of illness symptoms, with general support for a reduced incidence of respiratory illness being provided by a recent meta-analysis of data from 12 studies involving both athletic and non-athletic populations 1.
• Limiting alcohol intake to no more than 2 units per day and avoiding binge drinking is also essential, as it can negatively impact the functioning of immune cells 1.

From the Research

Vitamins for Preventing Routine Viral Infections

• Vitamin C: contributes to immune defense by supporting various cellular functions of both the innate and adaptive immune system, and supplementation with vitamin C appears to be able to both prevent and treat respiratory and systemic infections 2
• Vitamin D: can reduce risk of infections through several mechanisms, including inducing cathelicidins and defensins that can lower viral replication rates, and reducing concentrations of pro-inflammatory cytokines 3
• Multivitamins, Vitamin A, and Vitamin B: the effects of these vitamins in preventing and managing COVID-19 and long-COVID are contrasting, and no conclusion could be drawn on their efficacy 4

Recommended Intake

• Vitamin C: dietary vitamin C intakes that provide at least adequate, if not saturating plasma levels (i.e., 100-200 mg/day) 2
• Vitamin D: 10,000 IU/d of vitamin D3 for a few weeks to rapidly raise 25(OH)D concentrations, followed by 5000 IU/d, with the goal of raising 25(OH)D concentrations above 40-60 ng/mL (100-150 nmol/L) 3

Importance of Vitamins in Infection Prevention

• Vitamins play a crucial role in infection prevention and control, and their deficiency can result in impaired immunity and higher susceptibility to infections 2, 3, 4
• Multivitamin/multi-mineral supplement intake can help decrease micronutrient inadequacies and lower the risk of nutrient deficiencies 5