Does This Vitamin Really Help Colds and Flu?

One reason why the sale of vitamin C supplements skyrockets during the flu season is that there is a strong association between vitamin C and cold in the public mind. Therefore, cold symptoms are usually initially treated with different sources of vitamin C including orange juice as well as cough drops, chewable tablets and other dietary supplements containing vitamin C.

But how did the use of vitamin C in the treatment of cold and flu become established? The root of this association can be traced to Linus Pauling.

In his book, Vitamin C and Common Cold, the eminent researcher and two-time Nobel Prize winner argued for the benefits of vitamin C supplementation for preventing and treating cold.

Linus Pauling was a big advocate of high-dose vitamin C for treating a long list of chronic diseases.

While studies have confirmed that vitamin C can indeed boost the immune system, there is still an ongoing debate over the efficacy of the vitamin for preventing or treating cold and flu.

What is Vitamin C?

Vitamin C or ascorbic acid is a water-soluble vitamin and an essential nutrient. It functions as a major antioxidant and also a cofactor to essential enzymatic reactions in the body.

The major sign of vitamin C deficiency is scurvy, a disease caused by impairment of collagen synthesis.

The antioxidant property of vitamin C makes it useful for reducing oxidative stress. Therefore, the vitamin may contribute to lowering the risks of inflammatory diseases, diabetes, hypertension, and cardiovascular diseases.

Besides its antioxidant effect, vitamin C is also a natural antihistamine. In addition, vitamin C is essential to the immune system although the mechanisms by which it boosts the immune system are not clear.

However, the vitamin is found abundantly in cells of the immune system. Also, researchers believe that vitamin C may promote the activities of immune cells such as monocytes, phagocytes, lymphocytes as well as increase the production of cytokines.

The recommended dietary allowance for vitamin C ranges between 75 mg/day and 90 mg/day for adults. However, doses as high as 2,000 mg/day are still tolerable.

However, proponents of vitamin C megadoses recommend daily doses between 1,000 mg and 10,000 mg.

In such high doses, vitamin C is not used as a dietary supplement but rather as a drug in the treatment of a number of conditions.

The need for vitamin C mega dosage is highly debated within the medical community. This is because while some studies found that it may help, others find it useless and potentially dangerous. Although vitamin C is a water-soluble vitamin, users may still experience side effects and even toxic reactions when it is taken in excessive doses for prolonged periods of time.

Common side effects of vitamin C supplementation include indigestion, nausea, vomiting, diarrhea, flushing, fatigue, headache, skin rashes and sleep disturbance.

Sources of Vitamin C

Fruits and vegetables are the best dietary sources of vitamin C. Animal sources include meat but especially liver. Vitamin C can also be obtained from cod roe, oyster and milk.

Although orange juice is a popular source of vitamin C and commonly recommended for preventing and treating cold, it is not an ideal source of the vitamin.

Because the absorption of vitamin C in the intestine is partly controlled by channels sensitive to glucose, the extent and rate of its absorption of the vitamin are determined by the amount of glucose present on both sides of the intestine.

This means that high levels of sugar in the intestine and/or the blood will reduce the absorption of vitamin C.

This is important because orange juice (and most citrus fruit juices) have a high concentration of sugar. Therefore, delivering both sugar and vitamin C together does not improve the uptake of the vitamin into the blood.

Besides foods, vitamin C can also be obtained from dietary supplements. Studies have proven that the vitamin is just as easily absorbed from foods as supplements.

Vitamin C supplements are available in multiple forms ranging from tablets and capsules to crystalline powders and drink mixes. The vitamin can also be found in combination with other vitamins in multivitamin preparations or combined with other natural antioxidants such as rutin, hesperidin, and quercetin.

Can Vitamin C Help Cold?

Over 60 years of research into the benefits of vitamin C for preventing or treating vitamin C has only yielded inconsistent results. This means that there are well-designed studies that have found little use for vitamin C in the prevention of cold as there are good studies that concluded that the vitamin helped.

A summary of the results of these studies can be obtained from a review done by the Cochrane Collaboration on the subject.

According to the Cochrane review, it appears that vitamin C is not very useful in the treatment of a cold.

The evidence shows that after the onset of cold symptoms, vitamin C supplementation is useless. It does not reduce the duration of the cold or its severity.

When taken daily, studies show that vitamin C may shorten the duration of a cold by 8% in adults and 14% in children.

While these may seem like small effects on cold, its contribution can definitely reduce how long sufferers stay sick.

The best benefit for vitamin C supplementation in the prevention of cold is for those who partake in high-intensity exercises. Vitamin C can reduce the risk of coming down with a cold by 50% among people exposed to extreme conditions.

Therefore, regular vitamin C supplementation may not be the cure-all it is marketed to be but it can still cut your risk of catching a cold and especially provide significant protection if you are working under conditions of physical stress.

More Studies on Vitamin C, Cold, and Flu

Continuous Supplementation During the Winter Months

Researchers have demonstrated that vitamin C supplementation is more effective as a preventive measure rather than as a cure for a cold.

Therefore, supplementation should begin before you catch a cold and not after. But is this belief supported by hard evidence? The answer is yes.

In a study published in 2002 in the journal, Advances in Therapy, 168 volunteers were randomly assigned to take either placebo or a vitamin C supplement (2 tablets daily) over a 60-day period spanning the length of the winter months.

The results of the study showed that group receiving the vitamin C supplement had fewer incidences of cold and fewer days of severe symptoms than the placebo group.

This result shows that vitamin C supplementation during the winter reduced the risk of catching a cold and improved the speed of recovery. Therefore, the use of vitamin C supplements right from the beginning of the cold and flu season to the end may be justified as a preventive measure to avoid coming down with a cold or the flu.

Megadose or Not?

The need for high doses of vitamin C in the prevention of cold is still hotly debated among scientists.

While some researchers believe that megadoses of the vitamin are effective, others found no additional benefit for megadoses over regular doses. The 2 studies discussed below typifies both sides of the debate.

In a 1999 study published in the Journal of Manipulative and Physiological Therapeutics, a group of researchers investigated the benefits of megadoses of vitamin C in the prevention and treatment of a cold.

They recruited 252 students into the treatment group. Those who were already down with cold and the flu received 1,000 mg of vitamin C every hour for 6 hours and then the same dose 3 times daily. Those without cold and flu symptoms only got 1,000 mg of vitamin C 3 times daily.

In the control group, the researchers gave pain relievers and decongestants to 463 students.

The results of the study showed that megadoses of vitamin C improved cold and flu symptoms by 85% compared to the control group. The researchers, therefore, concluded that megadoses of vitamin C given before or after the appearance of cold and flu symptoms were effective for treating virus-induced respiratory infections.

On the flip side, a 2001 study published in The Medical Journal of Australia found no such benefits from taking megadoses of vitamin C.

In that study, the researchers recruited 400 volunteers over a period of 18 months. These volunteers were then divided into 4 groups. The control group received a daily dose of 30 mg of vitamin C while the other groups received 1,000 mg, 3,000 mg and 3,000 mg of vitamin C + other supplements.

In their results, the researchers found no difference in the duration or severity of cold between the 4 treatment options.

Therefore, they concluded that taking vitamin C in doses above 1,000 mg/day after the onset of cold did not provide additional benefits over low-dose vitamin C supplementations.

Cochrane Review

The verdicts of the Cochrane Collaboration are highly regarded because they are the results of independent reviews of well-designed studies.

A 2000 Cochrane review (updated in 2004) of the evidence for the use of vitamin C in the prevention and treatment of cold pooled 30 clinical trials on the subject. The reviewers found that taking vitamin C in doses as high as 1 g/day did not produce consistent results in the studies considered.

In their conclusion, they found that long-term vitamin C supplementation in large doses did not prevent cold but may reduce the duration of cold symptoms.

A Criticism

Even the Cochrane reviewers mentioned that the quality of the clinical trials they examined was variable. In fact, much of the vitamin C debate is neck-deep in bad science and flawed studies.

For example, a 1995 paper published in the Journal of the American College of Nutrition faulted the designs of a previous landmark (Chalmers’) review that found vitamin C ineffective for preventing and treating cold.

The authors noted that Chalmers did not consider the doses of vitamin C used in the studies analyzed in his review. Some of those studies used such low doses that it would have been impossible to see any benefit of vitamin C supplementation.

In addition, the authors pointed out that Chalmers used data that were different from the ones found in the studies he reviewed.

In their re-calculation, the authors found that megadose (1 – 6 g/day) vitamin C supplementation shortened the duration of cold symptoms by 21%.

Therefore, they concluded that vitamin C supplementation is indeed useful for preventing and treating the common cold.

Vitamin C Deficiency and Flu

If vitamin C may help your cold, is it useful for treating the flu? Studies suggest that vitamin C may provide specific benefits for preventing the flu.

In a 2006 study published in The Journal of Nutrition, a group of researchers investigated the effects of vitamin C deficiency on the progression of influenza infection in the lungs of mice.

Specifically, the researchers studied the influence of vitamin C deficiency on the response of the immune system to the influenza virus. They divided the mice into 2 groups. While one group served as a control, the other group was given daily doses of vitamin C for 3 weeks before both groups were infected with the influenza A virus.

The result of the study showed that populations of the flu virus were the same in the lungs of mice in both groups. However, vitamin C-deficient mice responded poorly to the infection.

The researchers found out that vitamin C supplementation was needed to boost the immune system and produce an adequate immune response to the invading flu virus.

Vitamins C and E and Flu

In another experimental study involving mice, a group of researchers compared the effects of vitamins C and E on an ongoing influenza virus infection.

The study was published in 2003 in the journal, Methods and Findings of Experimental Clinical Pharmacology. The researchers gave the mice daily doses of vitamin C alone, vitamin E alone and a combination of the two vitamins. Thereafter, the mice were infected with influenza A virus.

When studying the effects of the vitamins on the damage caused by the flu infection, the researchers found out that both vitamins provided antioxidant protections but vitamin E was more effective than vitamin C.

Compared to the use of the individual vitamins, the combination of vitamins C and E produced superior results.

This finding is in no way a recommendation for combining both vitamins in the prevention and treatment of influenza infections and further studies are needed to determine if such benefits can be observed in humans.

However, there is no harm in getting better antioxidant protection from vitamins C and E during this flu season.