Study identifies previously unrecognised cause of persistent coughing

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Generally in practice we’re able to make significant headway with all sorts of people with all sorts of health issues be they a 57 year-old man with type 2 diabetes or a 23 year-old woman with irritable bowel syndrome. And yet, I do inevitably come across patients I don’t seem to be able to help in any meaningful way, and this includes a handful of patients I’ve known over the years that suffer from a chronic, dry, tickly cough. These are individuals for whom conventional causes of cough, such as asthma, have been investigated and excluded.

I have, with these individuals, tried the sorts of approaches that one might expect from a naturally oriented doctor (e.g. identification and elimination of foods that might be triggering the problem, immune support if there’s any suspicion of compromise here, herbals approaches to soothe the throat and surrounding regions). But I have to say, hand on heart, that the results have generally not been good. Reading a study published yesterday on-line in the American Journal of Clinical Nutrition, I feel I may have found a missing piece in the puzzle regarding the causes of, and potential cure for, a persistent dry cough.

This study focused on vitamin B12, and the fact that a deficiency in this nutrient can lead to nerve damage. Could B12 deficiency lead to enhanced reactivity in and around the throat? And if so, might B12 supplementation help reduce this as well as the symptoms of chronic cough? [1].

This study focused on 42 individuals with chronic, unexplained cough. 27 of these were found to be deficient in vitamin B12 (<200 pmol/L). The remainder (15 people) were not B12 deficient.

The investigators found ‘laryngeal hyper-responsiveness’ (to histamine) was significantly more common in individuals with B12 deficiency than those without.

This finding is interesting, I think, and consistent with the investigators’ underlying hypothesis. But all this finding does, in essence, is link B12 deficiency with hyper-responsiveness in the throat – that does not mean that B12 is causing the hyper-responsiveness.

However, the investigators went a step further by treating the participants of this study with B12 to judge the effect. Individuals were treated with the following protocol:

1000 micrograms (1 mg) of B12 (in the form of cyanocobalamin) by intramuscular (IM) injection daily for 5 days, followed by;

1000 micrograms of B12 by IM injection weekly for 3 weeks, follow by;

1000 micrograms of B12 by IM injection once a month thereafter.

In the individuals who were not B12 deficient to start with, this treatment regime essentially did nothing for them. However, it was a different story in the group who were deficient: Here, B12 therapy reduced the ‘hyper-responsiveness’ in the throat significantly. Perhaps most importantly of all, cough symptoms reduced by about half in this group (though was unchanged in the group who were not B12 deficient to start with).

This is just one study, and as the authors point out, there is no other study like it (apart from one in Columbian children which found that giving them nutrient-fortified (including B12) snacks reducing coughing. However, bearing in mind how persistent cough symptoms can be, I know I’ll be on the lookout for B12 deficiency in the future.

I’ll be particularly keen to explore this possibility in individuals who fall into an at risk category. In this study, the most likely underlying cause of B12 deficiency was “inadequate intake of foods from animal origin”. Another potential underlying factor was low stomach acid secretion (stomach acid is required for the efficient absorption of B12).


1. Bucca CB, et al. Unexplained chronic cough and vitamin B12 deficiency. AJCN 19 January 2010 [epub before print]

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