SECOND UPDATE: From Sciencebased Medicine [no relation]: “While zinc has the ability to inhibit rhinovirus replication in the test tube, clinical trials for the treatment of colds have been disappointing. While there was a very modest improvement in symptom score in one study of adults, the benefit was seen only when zinc was taken in large doses 5-6 times per day. At these doses, GI side effects were significant and patients complained of a bad taste in their mouth. Needless to say, 5-6 times per day dosing with these side effects would preclude this as a viable option in children. Additionally, a well-designed, randomized, double-masked, placebo-controlled study demonstrated no effectiveness of zinc on cold symptoms in children and adolescents.”
UPDATE: I just took a look at the packet of Zn tabs I have, 15mg per tab. The Cochrane Review says effective dose seen at 75mg. So…who’ve I been kidding? Anecdote is not evidence.
Zinc is the only supplement I take if I feel a cold coming on. Vitamin C, echinacea, cod liver oil etc have no proven effect. But, recent Cochrane analysis vindicates earlier research on which I based my choice.
Zinc – The promise: Laboratory studies have found it can inhibit replication of the rhinovirus, the most frequent cause of cold symptoms.
The research: A Cochrane review of 18 good quality studies last month found that zinc lozenges or syrup significantly reduced the average duration of the common cold in healthy people when taken within 24 hours of the onset of symptoms.
Dr Mullen says: “Zinc influences the immune system in a number of ways: it is involved in immune cell recruitment and function, systemic inflammation, is an antioxidant, and may have antiviral properties with respect to the common cold.”
The verdict: A proven treatment for colds, although side effects include a bad taste and nausea. The review advises taking zinc lozenges of 75mg or more until there is more research.
There is one caveat, I remember my old GP telling me he was involved in a Cambridge U study on cadmium content of zinc supplements. Cadmium is toxic, don’t know what the conclusion of his research was, never been able to find it on PubMed. But, either way, it’s a risk-benefit equation you have to balance yourself. Just don’t waste your money on the remedies that are really nothing more than expensive placebos (homeopathy and Reiki therapy for instance), they will do nothing to tackle a viral or any other infection.
Work in 2001 suggested that cadmium can indeed be present in zinc supplements – http://www.ncbi.nlm.nih.gov/pubmed/11474903, other work highlighted the fact that zinc is protective acute exposure to cadmiu – http://www.ncbi.nlm.nih.gov/pubmed/23726800