No, but randomized controlled trials provide much more evidence than correlational studies. I'll admit I don't fully understand the methods these researchers us

No, but randomized controlled trials provide much more evidence than correlational studies. I'll admit I don't fully understand the methods these researchers use, so it's possible that they address the common problems, but historically conclusions from trying to establish causal relationships through data mining have not had a great track record. The bits I did understand seem solid enough (vitamin D and obesity levels 10-15 years ago, when the participants were enrolled, and now should be pretty highly correlated, and the sample size is pretty large) but there are a lot of non-obvious pitfalls when trying to establish causality with purely observational methods.