COSMOS-Web and replication
The results of COSMOS-Mind were seemingly bolstered by the recent publication of COSMOS-Web. Although I’ve seen this study described as having replicated the results of COSMOS-Mind, that description is a bit misleading. This was yet another ancillary COSMOS study; more than half of the 2,262 participants in COSMOS-Mind were also included in COSMOS-Web. Replicating results in the same people isn’t true replication.
The main difference between COSMOS-Mind and COSMOS-Web is that the former used a telephone interview to administer the cognitive tests and the latter used the Internet. They also had different endpoints, with COSMOS-Web looking at immediate recall rather than a global test composite.
COSMOS-Web was a positive study in that patients getting the multivitamin supplement did better on the test for immediate memory recall (remembering a list of 20 words), though they didn’t improve on tests of memory retention, executive function, or novel object recognition (basically a test where subjects have to identify matching geometric patterns and then recall them later). They were able to remember an additional 0.71 word on average, compared with 0.44 word in the placebo group. (For the record, it found no benefit for the cocoa extract).
Everybody does better on memory tests the second time around because practice makes perfect, hence the improvement in the placebo group. This benefit at 1 year did not survive to the end of follow-up at 3 years, in contrast to COSMOS-Mind, where the benefit was not apparent at 1 year and seen only at year 3. A history of cardiovascular disease didn’t seem to affect the results in COSMOS-Web as it did in COSMOS-Mind. As far as replications go, COSMOS-Web has some very non-negligible differences, compared with COSMOS-Mind. This incongruity, especially given the overlap in the patient populations is hard to reconcile. If COSMOS-Web was supposed to assuage any doubts that persisted after COSMOS-Mind, it hasn’t for me.
One of these studies is not like the others
Finally, although the COSMOS trial and all its ancillary study analyses suggest a neurocognitive benefit to multivitamin supplementation, it’s not the first study to test the matter. The Age-Related Eye Disease Study looked at vitamin C, vitamin E, beta-carotene, zinc, and copper. There was no benefit on any of the six cognitive tests administered to patients. The Women’s Health Study, the Women’s Antioxidant Cardiovascular Study and PREADViSE have all failed to show any benefit to the various vitamins and minerals they studied. A meta-analysis of 11 trials found no benefit to B vitamins in slowing cognitive aging.
The claim that COSMOS is the “first” study to test the hypothesis hinges on some careful wordplay. Prior studies tested specific vitamins, not a multivitamin. In the discussion of the paper, these other studies are critiqued for being short term. But the Physicians’ Health Study II did in fact study a multivitamin and assessed cognitive performance on average 2.5 years after randomization. It found no benefit. The authors of COSMOS-Web critiqued the 2.5-year wait to perform cognitive testing, saying it would have missed any short-term benefits. Although, given that they simultaneously praised their 3 years of follow-up, the criticism is hard to fully accept or even understand.
Whether follow-up is short or long, uses individual vitamins or a multivitamin, the results excluding COSMOS are uniformly negative.
Do enough tests in the same population, and something will rise above the noise just by chance. When you get a positive result in your research, it’s always exciting. But when a slew of studies that came before you are negative, you aren’t groundbreaking. You’re an outlier.
Dr. Labos is a cardiologist at Hôpital Notre-Dame, Montreal. He has disclosed no relevant financial relationships.
A version of this article appeared on Medscape.com.