A couple years ago, I wrote about a study that looked at the effect of a seawater nasal spray on the health of children (see that post).
Yesterday's New York Times, explored a very similar claim. Anahad O'Connor's column, "Really? The Claim: Gargling With Salt Water Can Ease Cold Symptoms," looks at a study of 387 Japanese adults aged 18 to 65 (see this page for an abstract). Treatment groups gargled with PLAIN water or a "povidone-iodine" solution. Those gargling with plain water did the best, with 0.17 URTIs (upper respiratory tract infections) every 30 person-days, meaning about 1 in 6 get a URTI per month if they gargle with water. The control group had a rate of .26, meaning about 1 in 4 got a URTI. The iodine group had a rate of .24, also meaning about 1 in 4 go a URTI.
So water looks pretty good. The only caveat, and it is the same as the issue I mentioned in the earlier post, is that the outcomes were self-measured. The people doing the gargling reported whether or not they had a URTI. IN Japan, where the study was performed, there is a strong bias toward water gargling, at least according to the abstract of the study, which says: "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)." In fact, the article reports that those in the control group gargled one time a day on average as well l (but those in the treated group gargled around 3 times a day). This affinity for water gargling and the belief that it stops infection may result in water-gargles reporting fewer infections, thus throwing the results of the study into question.
The New York Times, by the way, gives recommendations based on an upcoming book by Philip Hagen, to gargle with *salt* water, but cites this study, which is referring to *plain* water only.
My conclusion? If you THINK it is going to work, it's fairly likely water gargling will be effective, and it is a lot cheaper than buying some kind of preventative medicine. If you don't think it will work, this study provides little help in deciding whether it actually will work.