Well, firstly, most of those articles are actually quite strongly negative, which is weird. I mean, you’ve cherry-picked single sentences so that they appear to support your argument, but let’s look at the whole quote for the systematic review of vitamin D supplementation and hepatitis C. You’ve quoted the first sentence of the abstract’s conclusion. The rest:
“we observed that additional use of vitamin D has a positive effect on sustained viral response rates of patients with chronic hepatitis C infection. However, we cannot establish the efficacy because of substantial heterogeneity, a small sample size and a low methodological quality.”
So, essentially, this study is saying that it cannot be used as evidence for a conclusion because the research that has been done on the subject is not very good.
And your argument is filled with similar quote-mines. That 130-person pilot program with no placebo control arm and zero blinding that you quote? The whole sentence looks like this:
“In a sub-set of cases, corrective treatment with fish oil-based products has resulted in improvements in psychiatric symptoms without notable side effects…”
So no, fish-oil hasn’t been demonstrated to provide benefit to psychiatric patients (at least from this study) either.
But let’s say for a second that you’ve found definitive evidence that supplements work for these conditions. When was the last time that you saw fish oil pills marketed with the tagline “may improve psychiatric symptoms for those with psychotic disease” or vitamin D tablets marketed “may assist 30% of hepatitis C patients with minor improvements in viral load”?
Obviously, the answer is never.
What happens is that you get a finding like in one of these studies, a minor improvement in a single condition, and this is extrapolated into a much bigger-sounding benefit. Fish oil doesn’t provide “minor improvement in a single test of cognitive ability” it “may support brain health and cognitive function”.
So the main thing that is being sold with supplements, that diverse and discrete hope that they will improve not just one test score but every part of your thinking, is simply untrue. The statements are cleverly-crafted to conform to legal requirements, but they are still trying to sell to you something that just isn’t demonstrably true.
Supplements don’t work.