Recently, a two new studies of multivitamins and their efficacy for purposes other than vitamin deficiency were published in the Annals of Internal Medicine . One study looks at using multivitamins to improve outcomes after myocardial infarction, and finds no evidence of a benefit. The second study looks at measurable outcomes of cognitive function in men who take a multivitamin, and finds no positive benefit to supplementation. These are just two studies in a growing body of evidence (c.f. ) that shows that the primary and overwhelming thing that vitamin supplementation is good for is curing a vitamin deficiency. In general, there are many more popular claims about the wonders of vitamin supplementation than there are actual, high-quality scientific studies of those claims. The latest pair of articles were brought to my attention by a friend on Twitter, and what resulted from their post was a classic example of a bad argument.
I should note to readers here that vitamins have been shown to have benefits beyond curing a deficiency. As Scott Gavura over at the “Science Based Medicine” blog writes,
Not all vitamin and mineral supplementation is useless. They can be used appropriately, when our decisions are informed by scientific evidence: Folic acid prevents neural tube defects in the developing fetus. Vitamin B12 can reverse anemia. Vitamin D is recommended for breastfeeding babies to prevent deficiency. Vitamin K injections in newborns prevent potentially catastrophic bleeding events. 
The problem, as Gavura notes in his post and as I have said, is that there are more claims out there about “improving general health” than are tested by the scientific method, and those are unreliable at best and dangerously irresponsible at worst.
Since Twitter is a public forum, the person who engaged in the argument has no right to privacy and their communications are public record. I’ve gone to at least some length to hide their identity, but not in any way their words. Of course, you can find the conversation here: https://twitter.com/charlesdumais/status/413042077337804800.
Look at the pattern – it’s a classic example of a poorly constructed and unscientific argument against the two articles:
- Use the red herring that “scientists are just saying this because they have a strong vested interest”, e.g. money (argument fallacy)
- this is a red herring because even peddlers of alternative medicine could be argued persuasively to be “in it for the money”. It distracts from scientific assessment itself.
- Cite a non-scientific source that opposes the scientific articles. (poor scholarship)
- In this case, the arguer uses Mike Adams, the self-proclaimed “Health Ranger.” Adams makes money from peddling pseudoscience, and seems to have never met a pseudoscientific claim he didn’t agree with. He has no credentials as a medical or research doctor. He is totally credulous, and his only philosophy is to oppose the scientific method at every turn.
- Argue the source is good anyway (poor scholarship)
- Having failed to win over me about the quality of the source, dismiss my responses with a “well I believe it anyway” statement. (non-scientific argument)
Here you go. Enjoy!
 Lamas, G. et al. “Oral High-Dose Multivitamins and Minerals After Myocardial Infarction: A Randomized Trial” The Annals of Internal Medicine. 17 December 2013, Vol 159, No. 12.
 Grodstein, F. et al. “Long-Term Multivitamin Supplementation and Cognitive Function in Men: A Randomized Trial” The Annals of Internal Medicine. 17 December 2013, Vol 159, No. 12.
 Wang, Lu et al. “Systematic Review: Vitamin D and Calcium Supplementation in Prevention of Cardiovascular Events.” Annals of Internal Medicine, ISSN 0003-4819, 03/2010, Volume 152, Issue 5, p. 315.
 Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews 2013, Issue 1. Art. No.: CD000980. DOI: 10.1002/14651858.CD000980.pub4.