>>bookof+(OP)
Is it possible that this phenomenon is specific to people with those mental illnesses? A wider general population study resulted in the inverse effect:

https://www.mdpi.com/2072-6643/15/6/1354

I only did a postgraduate degree, so I don't have the practice reading scientific studies to determine which is true. Maybe someone with more knowledge can chime in?

>>devils+l7
Separately from this study, here's an interesting opinion piece by John Ioannidis titled "The Challenge of Reforming Nutritional Epidemiologic Research", published in JAMA 2018:

https://statmodeling.stat.columbia.edu/wp-content/uploads/20...

  > Assuming the meta-analyzed evidence from cohort
  > studies represents life span–long causal associations, for
  > a baseline life expectancy of 80 years, eating 12 hazelnuts
  > daily (1 oz) would prolong life by 12 years (ie, 1 year per
  > hazelnut), drinking 3 cups of coffee daily would achieve
  > a similar gain of 12 extra years, and eating a single man-
  > darin orange daily (80 g) would add 5 years of life. Con-
  > versely, consuming 1 egg daily would reduce life expec-
  > tancy by 6 years, and eating 2 slices of bacon (30 g) daily
  > would shorten life by a decade, an effect worse than
  > smoking. Could these results possibly be true?

via Andrew Gelman's blog: https://statmodeling.stat.columbia.edu/2019/01/26/article-po...

>>bookof+(OP)
Direct link to study: https://mentalhealth.bmj.com/content/28/1/e301700

>>devils+l7
It's well-known that schizophrenics self-medicate with coffee and nicotine: https://en.wikipedia.org/wiki/Schizophrenia_and_tobacco_smok...

The inverse possibility--that nicotine, and perhaps caffeine as well, heighten the risk of psychosis in those genetially predisposed--has also been considered.