Why links matter

I wrote last week about the importance of links.  Having links doesn’t guarantee the claims are justified, but it does make it a lot easier to check.  As an exhibit, consider today’s Stuff story about “Healing Foods for Spring Allergies“, which has lots of links.

• Garlic, we are told “has incredible antibiotic properties that can help clear mucous and fight infection.” There are two links. One is to a review article that summarise a lot of lab studies of allicin, a chemical in garlic.  These studies did not involve anyone, even mice, eating garlic — the chemical was applied directly to bacteria growing in Petri dishes.  The other is a review of a much wider set of studies of garlic and garlic extracts. Again, the studies are almost all in vitro, that is, “in lab glassware”.  This one contains the sentence “However, claims of effectiveness of garlic on common cold appear to rely largely on poor quality evidence”. And there’s nothing that even purports to be slightly related to “spring allergies”

• Vitamin C is supposed to be an “effective anti-histamine”.  The link to “clinical trials” refers to two studies in 1992, actually in people and published in real journals — though not available online through the journals’ websites.  However, the abstract of one of them is easily available online. It isn’t a clinical trial — it’s an uncontrolled before-after experimental study in healthy people — and they didn’t find the effect of vitamin C they were actually looking for.The other one was harder to find, and I don’t have an open-access source. It also wasn’t a clinical trial: it was an experiment in nine healthy  university students.  They started off getting 500mg/day of vitamin C — a level that could be achieved by a well-chosen diet — and then were escalated to 2000mg/day. There was no effect on blood histamine levels from 500mg/day, but a 40% lowering with 2000mg/day.  On the other hand “At the end of the third week of the study, two participants withdrew complaining of chronic diarrhea. Another reported diarrhea but completed the study. Osmotic diarrhea is considered the only major side effect of taking large doses of vitamin C (15). After several days at the 2,000-mg dosage level, two participants complained of dry nose and nosebleeds. Their dosage level was reduced to 1,000 mg daily and they completed the study without further complications. According to a document (JPI-HS-103-2) prepared in May 1991 by Janssen Pharmaceuticals of Piscataway, NJ, dryness of the eye, ear, nose, and throat is a common side effect of antihistamine drugs.” And, again, they didn’t even look at allergy symptoms.

• “If you suffer from sinus inflammation, pineapple is the fruit for you.”  The link is to a review of studies of pineapple extract for arthritis. Sinus inflammation is not mentioned.  Even for arthritis, the article says “The data available at present indicate the need for trials to establish the efficacy and optimum dosage for bromelain and the need for adequate prospective adverse event monitoring in such chronic conditions as osteoarthritis.”

• “Gargling salt water has recently been shown to help prevent upper respiratory infections in healthy people.” That’s quite a good study, but it compared plain water to water with povidone/iodine antiseptic.  It’s quite plausible that salt water also works, but the research didn’t show it.

• “Chicken soup is a wives’ tale with substance!”.  There are two links. One is to Mercola.com, and so isn’t going to be useful.  The other is to an in vitro study of mixing chicken soup extracts with neutrophils, a particular type of immune-related white blood cell.  It might be relevant if you were going to stick the chicken soup up your nose instead of drinking it.

There’s nothing wrong with these foods from a health point of view. I like chicken soup, although I prefer it with lemongrass, lime, and chili. But you’d expect the links to be to the strongest evidence available. And the disappointing thing is, they might well be.