Food, nutrients and relief from the common cold

Medical science has no cure for the common cold; symptomatic relief is the best we can offer as we wait for our body to overcome the viral illness.

Although the common cold is generally a mild disease and poses no real threat to overall healthy people it can be quite unpleasant. As a mom and a physician I really like having some helpful, natural, inexpensive common sense therapies to prescribe.

A good number of the methods used today haven’t changed much since my grandma’s time: Her advice was drink lots of liquids, get plenty of rest and eat chicken soup, but every grandma’s different and home remedies change from culture to culture.

Most of these home remedies pose no harm, and are well worth a try, even if there’s only an anecdotal notion of benefit. But I wanted to see if any of the remedies have attained enough scientific support through rigorous research so that we can now firmly say these kitchen-based medicines work better than a placebo, and there’s more than suggestion in their mechanism of action.

So, I headed to the online Cochrane library looking for reports on some of these natural remedies.

Before I get into the details of what I found, I’m sure you’ve been wondering how we make sense of study results when one study shows one finding while another study refutes those results. The experience can leave everyone quite confused, not knowing what to believe. But this is how the scientific method works. It’s only through refining and repeating studies that we can arrive at a tentative conclusion. The Cochrane reviews aim to do just that—take into account only the best of studies, and see if there’s enough evidence to prove efficacy.

The global Cochrane Collaboration is an independent network of volunteers that doesn't accept conflicted funding, and whose mission is to gather the best available evidence, summarize and interpret the results and make them readily available as a resource for evidence-based medicine on which to base scientifically grounded health-care decisions. (The full reports require a subscription, but the abstracts and summaries are free.)

Now, here are some interesting findings from the library:

Garlic

Garlic’s is a common-cold remedy handed down for generations in my husband’s family, and while I love garlic in cooking and use plenty of it, the result of a spouse consuming half a head of raw garlic is offensive to my nose. I just hate it! I admit I’m biased here; I really wanted this one to be proven ineffective.

The Cochrane report authors looked for randomized controlled trials of common-cold prevention and treatment comparing garlic with placebo, no treatment or standard treatment, and found five such studies with only one fulfilling their criteria. The study included 146 people and found that people who took garlic (in supplement form) every day for three months had fewer colds and fewer days of illness with a cold than people who took a placebo. They found no information from randomized, controlled trials about whether taking garlic at the time of a cold reduces either symptom severity or the number of days of illness.

They conclude:

“While this one study was positive, there is a need for large, high-quality randomised controlled trials to support these findings. Possible side effects in this small trial included odour and a skin rash. More information is needed about the possible side effects of garlic.”

Honey

Honey has been used from ancient times for many medical purposes, from wound healing to respiratory relief. Mixing honey into warm milk, tea or juice is a time-honored sore throat soother and cough suppressant.

The Cochrane reviewers looked for randomized, controlled studies comparing honey to placebos for the treatment of chronic cough, and found none that were applicable for review. In other words, there are no good studies out there, therefore no proof for or against honey for a four- week-old cough.

Honey for acute cough has shown promise in some studies, in which it outperformed both no treatment and cough syrup, and this treatment modality is currently evaluated by the Cochrane group.

A word of caution: Honey should not be given to kids younger than one year due to the risk of infant botulism.

Plenty of fluids

Drinking plenty of liquids makes sense: the water replaces losses due to rapid breathing, reduces the viscosity of mucus (therefore reducing congestion) and prevents dehydration. Alas, the reviewers found no evidence for or against increasing fluid intake during the illness—no randomized controlled studies have been conducted.

Vitamin C

Vitamin C was popularized by Nobel Laureate Linus Pauling in the 1960s and has been used widely as both a preventive and therapeutic agent for the common cold for decades. It’s still very controversial.

The Cochrane review was restricted to placebo-controlled trials testing at least 0.2 grams per day of vitamin C. Thirty studies involving more than 11,000 participants were analyzed and they showed:

• Regular ingestion of vitamin C has no effect on preventing the common cold in the ordinary population.

• Vitamin C reduced the duration and severity of common cold symptoms very slightly, and the magnitude of the effect was so small its clinical usefulness was doubtful.

• Six trials included participants exposed to short periods of extreme physical or cold stress or both (including marathon runners and skiers). In these people vitamin C reduced the common cold risk by half.

• Trials of high doses of vitamin C administered to treat the common cold showed no consistent effect on either duration or severity of symptoms. The authors call for more therapeutic trials (especially ones including kids who weren’t studied in trials) to settle the question.

Echinacea

Echinacea is a plant widely used for the common cold, but preparations vary greatly (there are many Echinacea species, and different parts of the plant are utilized in different ways). The Cochrane review found 16 clinical trials investigating the effectiveness of several Echinacea preparations for common-cold prevention or treatment.

Two trials using Echinacea for 8 to 10 weeks for common-cold prevention showed no clear effect.

Most of the trials investigated Echinacea for treatment of common-cold symptoms, and it seems that some preparations may be effective in adults, but the results were inconsistent. There’s no evidence of efficacy in kids. Side effects were rare, and included rashes in one trial in kids.

Zinc

Seven trials of variable quality were included in the review, and no strong evidence was found to show that zinc lozenges reduce the duration of the common cold. Side effects included mouth irritation, unpleasant taste and diarrhea.

As for chicken soup, I couldn’t find it in the Cochrane reviews. A study in CHEST (the cardiopulmonary and critical-care journal) looked at mucus velocity and airflow through the nose of 15 healthy people after they drank cold water, hot water or chicken soup. The results showed that both hot fluids increased the flow of mucus for about 30 minutes, with the chicken soup outperforming the hot water significantly. Another study in CHEST showed that chicken soup inhibited the movement of neutrophils (a subset of white blood cells) in the lab. So there is some evidence supporting my grandma’s regimen.

Writing this post and going through these studies reinforces my respect for the wisdom of traditional methods for symptom relief. Many of these old-fashioned remedies show some benefits, are worth a try, and won’t hurt. I think the current evidence on Echinacea, vitamin C and Zinc tend to show little or no efficacy, and zinc can have some nasty side effects, so I’d personally stay with the food remedies, and not the supplement ones—their safety profile’s better.

As to the garlic: I’m hoping my husband won’t read this post and decide on garlic as a preventive regimen, taken continuously. Personally, I think the secret to garlic’s success is that no one ventures near you when you eat that much raw garlic. Isolation is perhaps the best way to prevent the spread of communicable diseases, including the common cold. Washing hands frequently and well is probably the best preventive measure of them all.

Have a healthy fall,

Dr. Ayala