In times past, the "common cold" has been the most common respiratory infection worldwide. Scientists estimated that more than 200 unique viral strains could cause typical cold symptoms. 

Traditional cold symptoms include cough, runny nose, low-grade fever, sore throat, shortness of breath. Once resolved, the person is back to normal.

Simple strategies that may help strengthen the immune system and reduce the risk of upper respiratory viral transmission include the following.

  • Frequent handwashing using anti-microbial soap and warm water
  • Social distancing (reduces exposure to higher viral loads if someone nearby is ill)
  • Suppose you have a cough, cough into your sleeve, not your hand. This will help reduce the spreading of germs. 
  • Wear a protective face mask when indoors or as recommended based on the transmission risk in your local community. (Note: Masks can help reduce viral load exposure, which means your immune system does not have to work as hard to fight off as many pathogens. As the saying goes, "The poison is in the dose")
  • Consume a diet high in antioxidant containing foods such as colorful fruits and vegetables
  • Minimize intake of sugar, simple carbohydrates, and processed foods, which may weaken the immune system
  • Regular physical activity helps improve the immune system's response.

According to scientific research, the following supplements have been found to play a role in supporting a healthy immune system. 

Vitamin C

Vitamin C, also known as ascorbic acid or ascorbate, has been one of the most researched vitamins over the last 50 years. A search of the scientific literature reveals that over 55,000 studies have been conducted on vitamin C since 1968. Findings show that it helps promote a robust immune system and cardiovascular, brain, and skin health, among many other benefits. 

Many scientists believe that the human body could make vitamin C at one time but lost this capacity over time. Essentially, all animals, including most mammals, can make vitamin C—the exceptions are humans, monkeys, and guinea pigs. The brain and adrenal glands have the highest concentrations of vitamin C, 15 to 50 times higher than that found in the blood.

Vitamin C, also known as ascorbic acid, has been recommended to support immune health for decades. There still is no cure for the common cold, but a 2014 study suggests that vitamin C may help reduce the risk for developing a cold and reduce the duration of the cold compared to a placebo (sugar pills). More studies, however, are needed. 

Additionally, a 2021 study suggests that high-dose vitamin C might be beneficial in the early stages of a viral infection and pneumonia. It is believed that vitamin C helps improve the immune system, reduces inflammation and blood clotting. 

Suggested Dose: Vitamin C 500 mg to 2,000 mg daily

Vitamin D

In my Southern California Practice, 80 percent (4 in 5) of my patients are vitamin D deficient. The incidence is higher in less sunny climates around the world. I routinely recommend my patients supplement with vitamin D to optimize their immune systems.

A 2019 study in the International Journal of Environmental Research and Public Health found that those with higher blood levels of vitamin D were at lower risk for Upper Respiratory Infections than those with lower vitamin D blood levels. 

In a 2017 study in the British Medical Journal, researchers evaluated 25 randomized controlled trials which included 11,321 participants, whose ages ranged from babies to 95 years of age. 

In total, vitamin D supplementation appeared to reduce the risk of an upper respiratory infection by 12 percent. Those who had vitamin D blood levels less than 25 nmol/L (10 ng/dl) noticed the most significant benefit and saw a 70% decrease in infection rate when supplemented. In patients with a vitamin D level greater than 25 nmol/L (10 ng/dl), a 25% reduction in respiratory infections was seen.

Lastly, a 2021 meta-analysis study evaluated ten studies that included over 360,000 participants. The analysis showed that those with the lowest vitamin D levels were 43% more likely to become infected with a viral infection when compared to those with higher vitamin D blood levels. 

The suggested dose of vitamin D is 1,000-2,000 IU for children and 2,000 to 5,000 IU daily for adults. 


As we age, absorption of essential minerals like zinc may be increasingly impaired. Zinc is vital for the immune system to respond appropriately. The WHO or World Health Organization estimates that up to one-third of the world population is deficient in zinc. Additionally, poor dietary intake of zinc-containing foods or routine alcohol ingestion can result in chronically low zinc levels. Those over 65 years of age are more likely to have zinc deficiency compared to those under 65 years of age. 

The mineral zinc is also known to have both anti-inflammatory and antioxidant properties. 

Suggested dose: zinc lozenges, 30 mg as directed on the label. Also available in capsules and multivitamins.


Elderberry (Sambucus sp.), a flowering plant, has been used for hundreds of years for medicinal purposes by native populations worldwide. In recent years, elderberry's popularity has caught on. Indigenous Americans have used elderberries as a treatment for various infections and fever. 

A 2016 study suggests that elderberry may reduce the duration of cold symptoms in airline travelers. 

A 2019 study in Complementary Therapies in Medicine evaluated 180 participants. They found that elderberry could substantially reduce upper respiratory infection symptoms. 

Further, a 2001 and 2002 study both showed elderberry's benefit in strengthening the immune system response. This is key to preventing and fighting off any infection. 

Elderberry is available as a supplement, syrup, gummies, and lozenge.


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