Manuela Martinez and her colleagues were intrigued. Why was it that women who had suffered domestic violence seemed more prone to outbreaks of cold sores?
On the surface there appeared to be no connection between the physical and emotional abuse they suffered and the herpes infection that broke out on their lips. To try to find a link, they carried out a detailed profile of the saliva of a group of 74 survivors of abuse and compared it to a similar analysis of other women. They found that the abused women had far fewer immune-system compounds able to neutralise the virus. Their levels of antibodies to the virus were also lower. "Our findings confirm that the stress associated with partner violence could impair health by increasing the likelihood of viral reactivation and reducing the ability to suppress virus proliferation,'' says Dr Martinez, of the department of psychology at Valencia university.
The findings are part of a new and increasing body of evidence showing that the mind, personality and outlook can influence the development and progress of disease. New research, some of it being reported at an international conference on psychosomatic medicine this month, shows that the mind can have an effect on many conditions, from arthritis to cancer and heart disease.
Although Western medicine is still largely based on the paradigm that the mind and body are separate from one another, there is increasing evidence to the contrary. Such a mind-body connection has been hinted at down the centuries, but most of the evidence until now has been anecdotal or inconclusive. But a revival in interest in the mind-body link has triggered a wave of new research. Doctors in Holland who investigated heart disease treatments in almost 1,000 people found that patients with so-called type-D personalities - negative types who have difficulty communicating their emotions - were four times as likely to have heart problems. The same findings have now emerged from at least two other studies.
At Ohio State University, scientists have established that there is a mind-body connection in wound-healing. Their studies found that animals' skin wounds healed twice as quickly when they had social contact with other animals. "Stress delays wound-healing, and social contact helps counteract this delay," says Dr Courtney DeVries, who led the study.
And psychologists at Eastern Michigan University studied the outcome of bone-marrow transplants and found increased rates of survival among patients who were more defiant, better adjusted, and less depressed. "This first large-scale study provides evidence that psychosocial variables can affect survival,'' say the researchers.
The links don't stop there. Doctors in the UK and Germany looked at 1,300 elderly men and women over 10 years, and found a connection between personality and cancer deaths. "The results justify belief that certain types of cancer may be related to specific stress and personality factors,'' say the researchers. A Japanese study based on more than 30,000 people concluded that personality may affect mortality rates among cancer and cardiovascular disease sufferes. A second study found that skin cancer patients who had group therapy had higher levels of immune-enhancing cells. And in Los Angeles, scientists at the Digestive Diseases Research Center believe that the mind can even bring about chronic heartburn. "The presence of a severe, sustained life stress during the previous six months significantly increased heartburn symptoms during the following four months. As with other chronic conditions like irritable bowel syndrome, heartburn severity appears to be responsive to major life events,'' they say.
A large number of studies have shown that people who are depressed suffer greater levels of disease and illness, but research is increasingly showing that happiness and positive attitudes can have the opposite effect. Scientists in Finland carried out personality tests on 500 older people and then studied them for a decade. Fifty four per cent of the positive thinkers were still alive ten years laters, compared to 39 per cent of the others. Those with a negative slant on life were also six times more likely to be in institutional care at the end of the survey.
At Johns Hopkins University in Baltimore, researchers looked at the effect of humour on heart disease, and found that happy people were healthier. Not only were they less likely to get heart disease, they were also less prone to high blood pressure: "The results suggest that the propensity to laugh may contribute to cardio-protection,'' say the researchers. The mind-body link has also triggered new treatments. At Stanford University, one team found that metastatic breast cancer patients who were in a support group that used self-hypnosis as well as other mind-body techniques lived some 18 months longer than a control group.
With so much research now suggesting powerful mind-body links, the hunt is on for the mechanisms involved. How can abstract thoughts and feelings affect the body and influence the development and progress of diseases and conditions that are so diverse? Prime candidates for bridging the gap between mind and body include neurotransmitters, the nervous system, hormones and the immune system.
Stress is heavily implicated, with several studies showing that stressed people have lower levels of natural killer cells and are more vulnerable to disease. One study found that students taking exams had depressed immune systems, while others have shown links between high stress events such as divorce and redundancy and the onset of disease. People with a large number of friends and who also have pets have greater immune-system activity.
Stress is known to trigger physical reactions, especially in the flight-or-fight response to stimulus. But although it's known that stress can have an effect on the immune system, it is still not known how it can lead to a specific disease. Researchers in the relatively new area of psychoneuroimmunology, the study of how the mind and body interact in health and disease, are dedicated to discovering that mechanism.
One theory is that there is a direct communication system between the immune system, which orchestrates the body's defences, and the nervous system, which passes information between the body and the brain. Some experts believe that nerve endings in the thymus, spleen and bone marrow are evidence of communication.
But others maintain that the effects of the mind on disease are still unproven, and that any apparent effects can have different explanations. Are people with a large number of friends likely to live longer because of some unknown socialising effect, or because the friends are more likely to help them through illness? There are concerns too that mind-body explanations may have an adverse effect on patients with serious diseases, who may feel that they are in some way to blame.
"It is important to underline the hypothetical nature of these relationships,'' says Dr Vincent Jadoulle of the Université Catholique de Louvain. "Psychosomatic explanations risk being used to fill in knowledge gaps, and to give the illusion that we can avoid or control a disease. They especially risk making the patients feel guilty for their cancer or its development."