[Tharkun]

Don't have access to the full paper, but it seems like this study was based on asking patients whether they were taking supplements, as opposed to administering placebo/supplements and measuring the outcome. I would imagine that the worse your cancer is, the more likely you are to try things like supplements and whatnot. Did they manage to control for this?

[chiefalchemist]

> "...were queried on their use of supplements at registration and during treatment..."

My concern as well. Self-reported is a red flag. Not necessarily fatal but it obviously has an unpredictable affect on the data collected.

[fencepost]

I suspect that if you're the type to take a bunch of individual vitamin supplements then you know exactly what you're taking and how much, much more so than if you're taking a multivitamin every morning washed down with your coffee. There's also no reason to be lying about that to your doctor.

[phren0logy]

It's a reasonable concern, but all studies are flawed in some way. From the perspective of clinical practice, this is how most clinics assess supplement use - by asking the patient. In the absence of any better data (and it surely could be better) it at least offers some guidance when patients ask if they should or shouldn't take supplements during chemotherapy. I would tell them that there's limited evidence, but it points towards avoiding supplements.

[maxerickson]

I propose that for most people "I'm on chemotherapy" triggers the feeling that their cancer is pretty bad.