Many of the more dubious health sites promote gargling salt water (or peroxide) and swabbing the nasal cavity as a 'natural' prevention for catching the 'flu. Is there any science behind this? I understand how it alleviates symptoms through reducing swelling due to water being drawn out through the semi-permiable throat lining, but prevention?
Influenza viruses bind through hemagglutinin onto sialic acid sugars on the surfaces of epithelial cells, typically in the nose, throat, and lungs of mammals, and intestines of birds (Stage 1 in infection figure). After the hemagglutinin is cleaved by a protease, the cell imports the virus by endocytosis.
My doctor explained that if you do this regularly, you're washing the virus out before it can really grab hold in "Stage 1" of the infection.
This study (2005) found that gargling with just water (no salt) protects against respiratory tract infections:
BACKGROUND: Gargling to wash the throat is commonly performed in Japan, and people believe that such hygienic routine, especially with gargle medicine, prevents upper respiratory tract infections (URTIs). Its effectiveness, however, has not been established by clinical trials.
DESIGN: Randomized controlled trial carried out in 2002-2003 winter season and analyzed in 2003 and 2004.
PARTICIPANTS: Healthy volunteers (387) aged 18 to 65 years.
INTERVENTION: Participants were randomly assigned to water gargling, povidone-iodine gargling, and usual care (control). Subjects in the two gargling groups were requested to gargle with water or diluted povidone-iodine at least three times a day. Participants were followed for 60 days.
MAIN OUTCOME MEASURES: The primary outcome measure was first URTI incidence. Severity of URTI symptoms among incident cases was also evaluated. Both outcomes were assessed with a self-administered symptom record. Analyses were performed on an intention-to-treat basis.
RESULTS: A total of 130 participants contracted URTIs. The incidence rate of first URTI was 0.26 episodes/30 person-days among control subjects. The rate decreased to 0.17 episodes/30 person-days in the water gargling group, and 0.24 episodes/30 person-days in the povidone-iodine gargling group. Respective incidence rate ratios against controls were 0.64 (95% confidence interval [CI]=0.41-0.99) and 0.89 (95% CI=0.60-1.33). A Cox regression (proportional hazard model) revealed the efficacy of water gargling (hazard ratio=0.60, 95% CI=0.39-0.95). Even when a URTI occurred, water gargling tended to attenuate bronchial symptoms (p=0.055).
CONCLUSIONS: Simple water gargling was effective to prevent URTIs among healthy people. This virtually cost-free modality would appreciably benefit the general population.
Snopes has an article on this one.
"I don't even know of any evidence basis for gargling preventing influenza," Dr. Randy Taplitz (clinical director of infectious diseases at UCSD Medical Center) said.
Apparently this rumor was spread quite a bit during the Swine flu outbreak. It does apparently help for the symptoms of flu. From UHS health:
Gargling with warm salt water can moisten a sore or scratchy throat and temporarily relieve pain. Dissolve a teaspoon of salt in a glass of warm water four times daily. (Don't swallow the salt water, but spit it out.)
I actually can't find any references to it being a measure for prevention, rather just some symptomatic treatment.
Here is the search I used in case you want to research further:
According to an article published in Prescriber’s Letter, a prescribing journal for medical doctors, the benefits of gargling for the prevention of colds and flu is still unclear. A small study published in the American Journal of Preventive Medicine conducted by Japanese researchers showed that gargling with water was not only effective in reducing the incidence of the common cold, but it was also superior to gargling with an iodine solution.
Benefits of Gargling: Does It Prevent the Common Cold? by Kristie Leong MD