In a recent blog I admitted to having to eat a moderate sized portion of humble pie regarding vitamin supplementation and its possible benefits. This was a result of reading the COSMOS-Mind study which showed a statistically significant effect of multivitamin supplementation on cognition. The study authors concluded that “Daily multivitamin-mineral (MVM) supplementation for 3 years improved global cognition, episodic memory, and executive function in older adults.”

However, the plot now thickens further with this month’s publication of the VITAL study comparing Omega 3 and Vitamin D supplementation. In this 2,742 subject study there was a clear association between obesity and higher BMI with reduced efficacy of Vitamin D supplementation. Even when controlling for baseline vitamin D status, BMI was still significantly associated with changes seen with supplementation. The authors concluded "It really does seem that even with insufficient or low levels at baseline, those with higher BMI are not able to catch up to sufficient levels as well as those with normal BMI". Of course vitamin D is a fat soluble vitamin and it seems likely that the more fat you have the more vitamin D you might sequester. Another case of a confounding factor! Perhaps for future studies we should stratify in advance by BMI or perhaps do some retrospective analyses on existing publications.

I also had cause this month to revisit my recent piece on the imperviousness of some to evidence. A workman (who I have known for several years and gain quiet amusement from some of his gleanings from the wilder frontiers of the internet) visited to do a few minor repairs to my heating system, which had chosen our recent arctic spell as the perfect time to get temperamental. As he walked through the door he told me that thousands of old people had died because of the Covid vaccine and the Centre for Disease Control had confirmed this. I showed him the data from the Office for National Statistics which, of course, showed no such effects. Of course, and sadly, thousands of older people will die in any year and if you just look at the raw numbers you can rapidly conjure up a mare’s nest. The problem I believe is the superficial attractiveness to many of the conspiracy theory; it gives a simple answer to very complex problems.

However, it made me think that we should be wary of many peoples lack of appreciation of the difference between association and causality. This is always a problem for those working in drug safety: just because something follows something else does not mean that the first something caused the second. This is the post hoc fallacy, but it is a difficult thing to refute for many. I can still remember a patient with an advanced liposarcoma, obviously of quite long standing, telling me they thought it was due to having walked into a door the previous week. I think we all like to seek a cause for problems, but the “post hoc ergo propter hoc” fallacy is an indulgence we should be wary of in pharmacovigilance practice.

I promise as my (belated) New Year resolution to try not to bore further with multivitamins and conspiracy theories. However, you never know what lurks around the next corner… or the next journal that might set me off again!