"Psychosocial factors and public health: a suitable case for treatment?", Macleod & Davey Smith, 2003

Abstract
Adverse psychosocial exposure or "misery" is associated with physical disease. This association may not be causal. Rather it may reflect issues of reverse causation, reporting bias, and confounding by aspects of the material environment typically associated with misery. A non-causal relation will not form the basis of effective public health interventions. This may be why psychosocial interventions have, so far, showed little effect on objective physical health outcomes. This paper reviews evidence for the "psychosocial hypothesis" and suggests strategies for clarifying these issues. It concludes that, although misery is clearly a bad thing as it erodes people's quality of life, there is little evidence that psychosocial factors cause physical disease. In the absence of better evidence, suggestions that psychosocial interventions are needed to improve population physical health, in both absolute and relative terms, seem premature.

https://jech.bmj.com/content/57/8/565

 

Thought this was an interesting commentary, worth reading.

Much of the evidence for psychosomatic theories, for example about stress causing diseases such as heart disease or cancer, come from observational studies.

The authors highlight two problems in such studies:

Often the risk factor (e.g. self-reported stress) and outcome (e.g symptoms of heart disease) are both subjective so a relationship might simply reflect reporting bias. People under high stress might be more likely to report symptoms and complaints regardless of underlying disease. Studies usually try to account for this by adjusting for reporting tendency, but because this concept is difficult to measure accurately, there will likely be residual confounding.

The same applies for adjustment for socio-economic status. This is always measured quite imprecisely so that it is still possibly that a relationship between disease and psychosocial factors such as stress are confounded by factors that have to do with a low socio-economical status and that are not measured.​

Macleod and Davey Smith did a longitudinal observational study where the outcome was measured objectively and where stress was not associated with lower-socio economic status. The results support the points made above. There was a relationship between stress and subjective outcomes (such as angina) but not with objective outcomes. Those results were reported here:
https://www.bmj.com/content/324/7348/1247

 

Regarding this statement. I had a look at a recent review, such as this Cochrane review from 2017, which seems to confirm it. It states:

"there was no evidence that psychological treatments had an effect on total mortality, the risk of revascularisation procedures, or on the rate of non-fatal MI, although the rate of cardiac mortality was reduced and psychological symptoms (depression, anxiety, or stress) were alleviate."
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https://pubmed.ncbi.nlm.nih.gov/28452408/