Just out today is research testing if vitamin D supplementation impacts on the common cold. Key authors are from my local university, the University of Otago.

They conclude that vitamin D does not affect how often or severe people’s colds were,

“monthly administration of 100 000 IU of vitamin D did not reduce the incidence or severity of URTIs in healthy adults.”

[From abstract of paper. URTI = upper respiratory tract infection.]

This work is a randomized, double-blind, placebo-controlled trial testing 322 otherwise healthy adults. This type of trial is generally regarded as the ‘gold standard’ of trials for medical treatments.

Important differences to this work compared to previous trials of vitamin D (which also concluded it was ineffective in preventing URTIs) were,

  • a larger study[1] (better statistical power to draw a conclusion from)
  • vitamin D3 supplementation starting before the onset of winter, rather than during the middle of winter (when infections might have already taken hold)
  • the length of the study period, eighteen months
  • the large dose administered
  • robust collection of URTI data and sampling of viral infections

They found that very few of their subjects had vitamin D deficiencies. The authors point out that it is possible that vitamin D has an effect in the case of people with vitamin D deficiencies,[2]  You can see how this might make sense. In people with good levels of vitamin D, adding more might have no real effect. For those with low levels of vitamin D, the supplement raised their vitamin D levels to a normal level. This would have vitamin D not acting as a treatment per se, as a drug might, but to make up for a deficiency in patients lacking sufficient vitamin D that might cause them to struggle more than those with normal vitamin D levels. (e.g. they might find it harder to clear an infection.) Their results suggest that people with low levels of vitamin D that might benefit from this kind of effect are uncommon.

For this study, vitamin D supplements (or the placebo) were given monthly rather than, say, daily. The authors report that there are conflicting results depending on the dosage regime but note that arguments behind these are speculative.[3]

Another element is that as the study examines adults (aged 18 or older) results are not directly applicable to children.[4]

People already taking vitamin D supplements were not included (excepting those taking daily multivitamins with a vitamin D dose less that 400 IU) as were people taking medication that interfere with vitamin D metabolism or had one of several diseases that would interfere with the study.

The study was carried out in Christchurch, New Zealand. The winter of this study is that before the magnitude 7+ 4th September 2010 earthquake at Christchurch. (The more destructive earthquake occurred later on 22nd February 2011.)

Details of the trial registration can be found on-line.


Effect of Vitamin D3 Supplementation on Upper Respiratory Tract Infections in Healthy Adults: The VIDARIS Randomized Controlled Trial

David R. Murdoch, MD; Sandy Slow, PhD; Stephen T. Chambers, MD; Lance C. Jennings, PhD; Alistair W. Stewart, BSc; Patricia C. Priest, DPhil; Christopher M. Florkowski, MD; John H. Livesey, PhD; Carlos A. Camargo, MD; Robert Scragg, PhD

JAMA 308 (13) 2012.

The paper is free, i.e. open-access for all to read.


In the interests of my time and getting this out in a timely manner I have left aside a lot of detail. If readers would like a breakdown each of elements in the study, let me know I will consider it. (But allow this will take time.) Readers wanting a faster-paced read, without having to tackle the research paper proper, may prefer to read the author’s summary of their paper, which you will see has been a main source for my presentation here.

A question for my readers. New Zealanders may know of a recently-published book by Ian Wishart, the editor of the conspiracy theory-oriented Investigate magazine* titled: Vitamin D, is this the miracle vitamin? Does this book claim vitamin D to treat upper respiratory infections?

(* My initial impression is that it is an in-house publication – the publishing company, Howling at The Moon, appears to be owned by Investigate or Wishart.)

1. 351 were screened, 322 considered suitable, 294 (91%) completed the full study. For more details see the ‘Study Recruitment and Follow-up’ section of the Results in the paper.

2. These are measured as serum 25-hydroxyvitamin D levels. Only 5 of the 322 studied had vitamin D levels below 10 ng/mL. The authors cite a previous study that observed “vitamin D supplementation significantly reduced exacerbations only in patients with baseline 25-OHD levels less than 10 ng/mL”.

3. My own interests are pricked with the references to genetic variation in vitamin D receptors: “Alternatively, genetic variation in vitamin D metabolism or signaling may modify the anti-infective effects of vitamin D. Vitamin D receptor polymorphisms have been linked to both susceptibility to tuberculosis and response to vitamin D supplements in patients with tuberculosis. I can imagine some useful computational biology here (no doubt there is already work in this area).

4. You would have to offer why children were likely to have a different response, however. Although the lower age is just 18, the average age of participants was 47.

Updated to add the additional reading links, which in my rush I left out. Sigh.

Other articles at Code for life:

“We’re so used to getting a prescription that’s it’s surprising when we don’t”

Genetic tests and personalised medicine

Boney lumps, linkage analysis and whole genome sequencing

Rubella, not a benign disease if experienced during early pregnancy

Haemophilia – towards a cure using genetic engineering

Immunisation, then and now