[mensetmanusman]

Sorry, meant to post the connections people are researching between vitamin-D deficiency and obesity:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5691711/

[eurasiantiger]

Surprise: normal-weight people spend time sunbathing, while obese people do not.

This is a great example of why correlation does not imply causation.

[mensetmanusman]

Note that there are few ethical ways to prove single variable causation over long times in human studies :)