Stress caused by conflicts at home or work may increase the risk of breast cancer, scientists said yesterday.
A 24-year study of women in Sweden, which began in the late 1960s, has shown that those who reported high levels of stress at the start - including tension, fear, anxiety and sleeplessness - were twice as likely to develop breast cancer as those with low levels of stress.
But the study's lead author, Osten Helgesson, warned that the findings were not definitive and that women should not blame themselves for their cancer - a common problem among patients with the disease. The results were presented to the European Cancer Conference in Copenhagen yesterday.
The researchers from the Sahlgrenska Academy in Sweden interviewed 1,350 healthy women in 1968 and asked them if they had suffered stress for a month or longer in the previous five years. Over the next two and a half decades they found that of 456 women who had experienced stress, 24 (5.3 per cent) developed breast cancer. Of 894 women who said they suffered no stress, 23 (2.5 per cent) developed breast cancer.
Scientists have examined the link between stress and cancer for more than a decade. Despite a series of studies, no clear findings have emerged. Dr Helgesson, a GP from Gothenburg in Sweden and a doctoral student at the Sahlgrenska Academy, said he believed his study was a stepping stone on the way to establishing whether stress could predict cancer.
If so, women suffering from stress could be selected for preventive treatment or early detection such as screening.
Dr Helgesson said: "Although our study does show a significant association between stress and breast cancer, I would emphasis that more research needs to be carried out before it can be said that stress definitely increases a risk.
"Ours is one of only a very small number of prospective studies, and although our findings are significant, more and larger prospective studies need to be done."
The women in the study were interviewed in 1968 and asked whether they had experienced stress for a month or longer in the previous five years. They had follow-up examinations in 1974-75, 1980-81 and 1992-93, but they were not asked about stress again. The study therefore relates to stress that they experienced during one period of their lives in the mid-1960s.
Dr Helgesson told the conference that the findings had taken account of differences such as weight, smoking, drinking, family history and whether the women had children, all of which are known to affect the risk of breast cancer.
Britain's leading expert on stress and cancer, Professor Amanda Ramirez of Guy's and St Thomas' Hospitals, London, who has studied the relationship between the two for more than a decade, said recent research had failed to show a link.
"This study stands on its own. Its methodology is questionable and it is out of step."
'I developed disease after suffering panic attacks'
When Mary Morrissey was diagnosed with breast cancer in 1999 at the age of 40, her first thought was that stress must be the cause. "I had six sisters and a mother who were all alive and none had cancer. So there was no family history. I had breastfed my children and been active all my life. I thought it had to be stress," she said.
She had good reason for thinking so. Ten years earlier she had gone through an acrimonious divorce, which included a custody battle for her three children. It was a traumatic time. "Someone told me it takes ten years for a cancer to develop - I was divorced in 1990 and diagnosed in 1999," she said. "I do think that was the reason for my cancer. I suffered panic attacks and my stress levels were very high. After the divorce I was on my own for 10 years with the three children, doing a full-time degree and working seven days a week."
Today, Ms Morrissey is free of the disease. She still takes drugs for the cancer but has suffered no side-effects. She walks 30 miles a week and has lost 24kg (53lb) since her treatment was completed.
She has more energy now, she said, and she takes care to avoid stress. "I have learnt a great deal in the last decade or so," she said. "I won't allow things to upset me. I go to the gym and to meditation classes to keep my head in order because if you don't do that everything else falls apart. But I feel very well."Reuse content