It’s that time of year again—sniffles, coughs, and fevers start making their rounds, and more often than not, the flu is behind it. The flu is one of the most common illnesses, responsible for millions of cases annually. According to the CDC, during the 2022-2023 flu season, an estimated 27 million people in the U.S. contracted the flu, leading to over 300,000 hospitalizations. This contagious respiratory virus can sneak in like a typical cold but hits hard with fever, fatigue, and body aches, making it a major disruptor for families. Thankfully, I have a hero in my toolkit: supplements! And every family should have theirs, too.

At my Ridgefield, CT clinic, I always incorporate supplements into the care plan I recommend to families because, let’s face it, not everyone can get all the necessary nutrients through their diet alone. Supplements help fill those gaps and support overall health.

With the right immune-boosting arsenal, you can give your body the support it needs to fight off viral infections and spare your family a lot of stress and discomfort. Supplements can help the body build a barrier to illness by creating wellness from within. The healthier our bodies are, the better we can repel and tolerate illnesses, including viruses and the flu, by enhancing immune system function.

Here’s a list of evidence-based vitamins and minerals for supporting the immune system.

1. Vitamin D

Vitamin D is involved in so many functions in the brain and body. High dose vitamin D has been shown to reduce inflammation in those with chronic lung conditions. Vitamin D₃ is made in your skin through a chemical process called “photolysis” that occurs when you expose your skin to ultraviolet B rays. In the liver, vitamin D is turned into a chemical called calcidiol and this vitamin D prohormone travels through the bloodstream to the kidneys, where it’s turned into the active form. Every tissue in the body has vitamin D receptors, including the brain, heart, muscles, bone health, endocrine system, and immune system, which means vitamin D is needed at every level for the body to function. 

Upwards of 70% of Americans have vitamin D deficiency, leading to significant medical and psychological consequences. Low levels of vitamin D are associated with anxiety and depression (Bičíková et al., 2015). In terms of anxiety and mood, if the brain and endocrine system are not getting enough vitamin D, then they can’t work properly, then these symptoms can result.

Vitamin D supplements play a role in magnesium homeostasis, which is necessary for so many biochemicals in the body. If you have a mental health issue, it is important to have your vitamin D levels checked. For those with clinical conditions, your blood levels of vitamin D should be on the high end of average.

Sun exposure is a natural source of vitamin D, as the skin produces this essential vitamin when exposed to sunlight. The best time for vitamin D synthesis is typically between 10 a.m. and 3 p.m., and just 10-30 minutes of midday sun exposure several times a week can help maintain healthy levels, depending on skin type and location.

Dosage: To maintain adequate vitamin d levels, only 400 to 800 IU (15 to 20 mcg) is required daily. To boost low levels or immune systems, higher doses, such as 2,000 to 5,000 IU daily.

2. Vitamin C

About 7% of the U.S. population is estimated to have vitamin C deficiency, particularly among smokers and those with limited access to fresh produce. Vitamin C or ascorbic acid contributes to immune defense by supporting various cellular functions of both the innate and adaptive immune systems. It helps white blood cells that help to fight infections. Intravenous vitamin C has been explored for its potential benefits for critically ill patients, particularly those with COVID-19-related complications like sepsis and acute respiratory distress syndrome. Vitamin C is also important for iron absorption, and iron deficiency can make you more vulnerable to infections in general. A natural way to ensure you have adequate vitamin C is by consuming vitamin C in form of citrus fruits and plant foods such as oranges, lemons, limes, and grapefruits.

Research suggests that supplementation with vitamin C appears to be able to both prevent and treat respiratory and systemic infections. Vitamin C has long been used to treat the common cold symptoms and helps to reduce the duration (Hemilä H et al., 2013). The research is mixed for taking high-dose vitamin C (e.g., 500 mg twice daily) before getting a cold but it may slightly reduce the severity and duration of a cold. (Carr AC et al., 2017)

Dosage: 1 to 2 grams in children and 6 to 8 grams in adults

The NIH has more dosage recommendations, here

3. Vitamin A

Vitamin A is known for its anti-inflammation properties because it improves immune function. It plays regulatory roles in cellular immune responses and humoral (body fluids) immune processes. Research suggests that a therapeutic effect of Vitamin A in the treatment of various infectious diseases. According to Huang et. al (2018), “Vitamin A has both promoting and regulatory roles in both the innate immune system and adaptive immunity; therefore, it can enhance the organism’s immune function and provide an enhanced defense against multiple infectious diseases.” A research study from 2015 found that Vitamin A supplementation trained the body to “forget” past infections. 

Dosage: 

*Too much Vitamin A can be toxic

Tolerable upper limits of a daily dose according to Web MD:

ADULTS:

Vitamin A is 10,000 units (3,000 mcg)

CHILDREN:

For birth to 3 years, 600 mcg/day (2,000 units)

 4 to 8 years, 900 mcg/day (3,000 units)

9 to 13 years, 1700 mcg/day (5,667 units)

14 to 18 years, 2800 mcg/day (9,333 units).

For measles: 100,000 to 200,000 IU of vitamin A for at least two doses has been used in children less than 2 years-old.

4. Zinc

Zinc supplements can be beneficial in reducing the duration and severity of acute respiratory tract infections by supporting immune function and fighting off pathogens. Zinc has antioxidant properties and has anti-inflammatory actions, as well as anti-viral properties. Zinc may also help reduce the severity and duration of upper respiratory tract infections. Research suggests that zinc supplementation decreased oxidative stress markers and generation of inflammatory cytokines. Zinc has been shown to reduce the severity and duration of colds, which are caused by viruses. It inhibits viral replication and has antiviral effects.

Zinc deficiency can weaken the immune system, but you can boost your levels by including zinc-rich foods like meat, shellfish, legumes, seeds, and nuts in your diet. Eating nutritious foods is a sure fire way to stay healthy and to prevent viral infection.

Dosage: 80 to 150 mg daily for adults; 3 to 11 ms daily for children

5. Elderberry

Elderberry has been used for centuries to boost the immune system and fight viruses, colds, and sinusitis. Elderberry dietary supplement has been shown to help alleviate symptoms of acute respiratory infections, providing a natural boost to the immune system. Research suggests that elderberry extract has been shown to inhibit the replication and hemagglutination of human flu viruses, including certain strains of Influenza A and B. It has also been shown to shorten the duration of the flu. Boosting antiviral immunity with supplements like elderberry can help the body defend itself against viral infections.

Dosage: 15 ml of elderberry syrup 4 times per day

6. Beta-Glucan

Beta-glucans are naturally occurring polysaccharides. Beta-glucans are glucose polymers are constituents of the cell wall of certain pathogenic bacteria and fungi that bind surface receptors to activate immune cells (Akramiene et al., 2007).  Research suggests that these substances increase host immune defense by activating the complement system, enhancing white cell and natural killer cell function and reducing oxidative stress.

Dosage: varies between 50 and 1,000 mg daily

7. Garlic

Garlic produces a chemical called allicin that is active against microbes and gives garlic its distinctive smell. Allicin, a compound found in garlic, is an antiviral agent and is known to have antibacterial, antifungal, antiparasitic, and antiviral properties. Garlic has been shown in laboratory studies to inhibit certain flu and cold viruses Ahmadniaye Motlagh et al., 2019) It has even been studied and found to shorten the duration of the flu and treat pneumonia (Weber et al., 2020). Dietary supplements containing garlic offer a convenient way to incorporate its health benefits into your daily routine.

Dosage: Maximum dosages are: 

• 17.0 grams for a 150lb person
• 22.7 grams for a 200lb person
• 28.4 grams for a 250lb person

8. Basil

There are a number of types of basil, which differ in taste and smell. Two of the most common are Sweet Basil (Lamiaceae) and Holy Basil (Tulsi). Basil contains a wide range of essential oils, rich in phenolic compounds, and a wide array of other natural compounds (more than 25), including polyphenols such as flavonoids and anthocyanins. Basil has been used for centuries as a traditional and ayurvedic medicinal plant for the treatment of headaches, coughs, diarrhea, constipation, warts, worms, and kidney malfunctions.

Today basil is often used as an immune booster and an anti-inflammatory herb, as well as for its antibacterial and anti-aging properties. Animal and human studies support basil having multiple therapeutic actions including adaptogenic, antimicrobial, anti-inflammatory, cardioprotective, and immunomodulatory effects. Research suggests that Basil counters metabolic stress through normalization of blood glucose, blood pressure, and lipid levels. 

Dosage: 300 to 1200 mg a day 

This is all uncharted territories but trying to support your nervous system and body with good nutrition, hydration, exercise, sleep, hygienic practices and adding in vitamins to boost your immune system is the best way to protect yourself.

Other Supplements to Improve the Immune System

9. Magnesium

Magnesium plays a crucial role in immune system regulation by activating key immune cells like T cells. It also helps reduce inflammation, supporting a balanced immune response. Maintaining healthy magnesium levels strengthens the body's defenses, helping it respond more effectively to infections.