It is time that the health-care system abolished the artificial division between mental and physical health and treated the whole patient. The dichotomy between mind and body is rooted in the work of Descartes in the 17th century - and belongs there.

Today there is an urgent need to strengthen the provision of mental health care to people with physical illness and the quality of physical health care provided to people with mental health problems in both acute and primary care. Failure to treat both physical and mental health conditions results in poorer health outcomes and higher health-care costs.

With the intensifying interest in and concerns about disease prevention and health promotion, mental health solutions, like those for physical health, must be rooted in a population-based public health model. Such a model is characterised by concern for the health of a population in its entirety and by awareness of the linkages between health and well-being and the physical and psychosocial environments. One obvious corollary is that all health-care professionals, including those who work in public health, need more education and training about these linkages. Both mind and body are affected by biological and emotional changes, as well as by socioeconomic factors such as income and housing.

Children with chronic illness are at considerable risk for psychiatric disorders, and this risk, together with that for social adjustment problems, increases when disability is also present. This means that doctors who care for children with chronic health problems should be skilled in the recognition of existing or incipient mental health and social problems and familiar with preventative and treatment approaches to lessen their impact.

Mental health problems in those with chronic physical illnesses are easily missed by health care professionals whose focus is on the physical disorder which is usually the reason for the consultation. Mentally ill people may be unable to comprehend or describe their physical symptoms adequately and their physical health may be overlooked if their doctors are not aware and vigilant in assessing the patient's total health status.

While public health professionals understand well the impact of socio-economic factors such as unemployment, poverty and housing on physical health, they are less aware of the correlation between these social determinants and mental health. But there is now good evidence that the poorer an individual's socioeconomic conditions, the higher their risk for mental disability.

Sound social policies can provide an effective buffer against these mental health risks, especially for vulnerable groups like children, immigrants and the socially isolated. There is a growing body of research to help elucidate the biomedical basis of the relationship between physical and mental disorders. Mental illness can alter hormonal balances, sleep cycles, and immune system function, creating an increased vulnerability to a range of physical health problems. People with long-term psychological stress, depression and post-traumatic stress disorder are more likely to develop physical illnesses such as stroke, dementia, heart disease and diabetes at younger ages.

And just as techniques such as psychotherapy have been shown to alter brain structures, now there is also evidence that child abuse can cause genetic alterations within the brain.

Recently scientists have found that depression and major stress cause the same chromosomal changes that happen during ageing.

This accelerated ageing process is reshaping the understanding of stress and depression as not just psychological conditions or even brain disease, but as systemic illnesses in which mood may simply be the most obvious symptom.

The ultimate aim of this chromosomal research is to find the molecular mechanisms by which depression and stress take their toll on the body.

That might also help with understanding why some people appear to have innate biological and social protective factors.

But with or without this knowledge, the holy grail of health care should be to ensure a holistic approach to the prevention, early intervention and treatment of mental and physical disorders, regardless of the underlying causalities.

Dr Lesley Russell is a Research Associate at the Menzies Centre for Health Policy, University of Sydney.