> Most likely healthy people go outside more than sick people and thus get more sun exposure

Such a lazy critique.

Here's the actual study: https://onlinelibrary.wiley.com/doi/10.1111/joim.12251

Number of subjects: 39,973

Follow up period: 20 years

Some factors controlled for: smoking, history of antidiabetic meds, history of CVD meds, weight/height/BMI, level of exercise, income, alcohol consumption, N pregnancies.

I think these factors pretty well correlate with "health" (however you'd measure actually that).

That's what the authors say:

> Despite having adjusted for several potential confounders, the major shortcoming of this study is the inability to distinguish between the consequences of an unhealthy lifestyle and of avoidance of sun exposure.

Take depression for example. None of the factors you mentioned would control for it and depression is often not diagnosed, especially early on.

And I'd guess smokers go outside more than non-smokers.

Surprise, the study designers did happen to also think to control for smoking.

Agreed, and you already addressed this with your sibling comment. I just thought it was an amusing counterpoint to "healthy people go outside more than sick people".