Flu – Food Supplements

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Flu - Food Supplements
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Flu - Food Supplements

The following foods and supplements have all shown potential for either preventing flu infection or for treating flu symptoms. The Flu - Food Supplements page is regularly up dated as new evidence is published in the medical journals. 


There have been several studies of the use of NAC to prevent and treat influenza symptoms – especially the inflammatory effects of chronic obstructive pulmonary disease (COPD), one of the most dangerous results of influenza.

A large study of older adults who took 600mg twice daily of NAC for six months, found that only 25% of them experienced influenza-like episodes, compared to 79% in the placebo group. Of those who were ill, the NAC group were less ill and spent less time in bed. The study’s leader, Dr. Silvio de Flora, said that NAC appeared to reduce the oxidative and inflammatory burden within lung tissue through multiple mechanisms.

A 2011 trial found NAC helpful in the management of COPD symptoms and that the supplement inhibited influenza virus replication and diminished the amount of inflammation. It concluded, “this work supports the use of (NAC) antioxidants in order to ameliorate the inflammatory effects of different viral infections during COPD exacerbations.”


A 2012 randomized, double-blind, placebo controlled study on aged garlic extract aimed to prove it could modify immune cells. Of the 120 healthy people on the trial, 60 were given 2.56 grams per day of aged garlic extract. After 90 days illness diary entries showed the incidence of colds and flu between the two groups were not statistically different but that the group consuming aged garlic extract had less serious illness with milder symptoms and a reduction in the number of days when they functioned sub-optimally due to illness. They concluded, “these results suggest that supplementation of the diet with aged garlic extract may enhance immune cell function and that this may be responsible, in part, for reduced severity of colds and flu.”


Studies into the effectiveness of Vitamin C (L-ascorbic acid) against flu have had mixed results over the years. However, trials in 2012 and another in 2013 found Vitamin C shows anti-viral immune responses at the early time of infection. A Chinese study found that the antiviral effect was dose-dependent. 2.5 mmol/L of Vitamin C could eliminate 90% of the viruses while they reported 20 mmol/L totally blocked viral replication in vitro. The antiviral effect of pharmacological Vitamin C varied at different phases of infection, but it was concluded that “Vitamin C, as a pro-drug, eliminates or kills influenza virus, probably by producing steady-state concentrations of hydrogen peroxide (H2O2) in extra cellular fluid.


Many people are surprised to discover that Vitamin D, not C, is the real superhero of anti-flu food supplements. When scientists noticed a reverse linear association between influenza and respiratory infections on the one hand, and Vitamin D on the other, a number of studies were instigated.

The flu virus is most common during the winter when sunlight levels are lowest, the weather is cold – which hinders white blood cells from reaching the respiratory tract and fighting the virus, and humidity is low – dry air allows the virus to live longer outside of the body.

Vitamin D boosts the body’s immune system and reduces inflammation. This helps to fight off infections initially and, if the body is infected, to keep temperatures lower so the lung lining is less aggravated making it harder for bacteria to give rise to pneumonia. In a 2012 review of 5 clinical Vitamin D trials, it was concluded that all the results pointed to the fact that supplementation with Vitamin D significantly degreases respiratory tract infections.

Dosage recommendations from studies are between 1000 – 5000 IU / 25-125mg per day of Vitamin D during the influenza season. Combining this with anti-influenza vaccines provides the best protection against the type A virus. Trials have shown less spectacular results again type B virus.


The antioxidant effects of Vitamin E help the body to produce the antibodies it needs to fight germs and harmful cells. In a 2003 trial Vitamin E was shown to have a stronger preventative effect than Vitamin C, but the combination of E and C was stronger still. In a 2000 trial on the long term use of antioxidants to reduce influenza infection, of the antioxidants tested Vitamin E was the only one to significantly reduce pulmonary viral titers which helped to stop flu patients from suffering decreased appetite and weight loss. The daily recommended intake for Vitamin E is 60-100mg. It can be obtained from sunflower seeds, vegetable oils and grains, or taken as a supplement.


Selenium is a trace mineral needed for the correct function of the thyroid gland. It assists the immune system and has recently been discovered to be important in stopping the flu virus from mutating.

Scientists found that animals who were deficient in selenium were more likely to contract infectious diseases, but in the case of the flu virus it was discovered that the initial virus mutated in the selenium deficient host into a far more virulent form.

Selenium deficiency can lead to joint pain, unhealthy hair and white spots on fingernails. Excess selenium results in bad breath, diarrhea and occasionally hair loss. The recommended daily intake is 70mg and it can be found in nuts – especially Brazil nuts, seafood, oily fish, whole-wheat bread, seeds, mushrooms and whole grains.


There is some evidence that zinc lozenges, syrup or tablets can speed recovery from influenza if taken within 24 hours of symptoms beginning. In a 2011 study it was shown that children who were given a zinc supplement at the time of their flu vaccination suffered less malaise side effects from the infection. Long term use of zinc is not recommended and can result in unpleasant side effects including vomiting and diarrhea.

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