For years, a belief has circulated in wellness communities and doctors’ offices alike — that intense psychological stress, grief or a negative personality could bring on cancer.

But a massive international study has put that theory to rest, finding that a person’s state of mind has very little to do with the development of the disease.

The research — published March 23 in the journal Cancer — analyzed data from an international research consortium funded by the Dutch Cancer Society.

The analysis included data from 421,799 people in the Netherlands, United Kingdom, Norway and Canada. 

Scientists looked at whether factors like neuroticism, social support, general distress and relationship status or the loss of a partner, measured at a single point in participants’ lives, influenced who eventually got cancer.

After a 15-year follow-up, the results were clear: There was no evidence that psychosocial factors increased the overall risk of cancer.

Specifically, the study found no direct connection between a person’s mental state and their likelihood of developing breast, prostate or colon cancers.

The Psychosocial Factors and Cancer (PSY-CA) consortium “has spent the last years researching a commonly held belief — that poor mental health or other potential psychosocial stressors can increase the risk of developing cancer," said lead author Lonneke van Tuijl of University Medical Center Groningen in the Netherlands. 

"Our findings do not support this notion,” she added in a news release.

The study did initially find a slight increase in lung cancer risk among people who felt lonely or had recently suffered a loss.

But when the researchers accounted for known risk factors — like whether the person smoked or had a family history of cancer — that link almost entirely disappeared.

The researchers concluded that while stress itself doesn't cause cells to become cancerous, the way people react to stress can.

People going through a difficult time might be more likely to smoke, drink alcohol or eat poorly, which are the true drivers of cancer risk.

“Furthermore, many of the small effects observed are often explained by unhealthy behaviors,” van Tuijl said.

While maintaining good mental health is vital for quality of life and recovering from illness, the study showed it is not a primary shield against getting cancer in the first place.

They also noted that the findings may help those with cancer avoid guilt and self-blame from attributing their cancer diagnosis to a stress factor in their life.