I Want To Believe... But I Think There's a Causality Direction Issue Here

From April 1, 2014 CBS Atlanta:

A new study from the Medical University of Graz in Austria finds that vegetarians are more physically active, drink less alcohol and smoke less tobacco than those who consume meat in their diets. Vegetarians also have a higher socioeconomic status and a lower body mass index. But the vegetarian diet — characterized by a low consumption of saturated fats and cholesterol that includes increased intake of fruits, vegetables and whole-grain products — carries elevated risks of cancer, allergies and mental health disorders.

Vegetarians were twice as likely to have allergies, a 50 percent increase in heart attacks and a 50 percent increase in incidences of cancer.

I have always regarded vegetarianism as a health goal as pretty silly.  (Three pounds of meat a day, however, is definitely dangerous.)  George Orwell's The Road to Wigan Pier has a ferocious attack on what he regarded as the lunatic fringe cultural aspects of English socialism, including vegetarianism.  (For those who are vegetarian for ethical reasons, I don't agree, but I can respect our differences.)

Nonetheless, I find myself suspecting that some significant number of people who are vegetarian may be because they have significant health problems (including mental health disorders), and have become vegetarian for that very reason.  Which causes which?