Poor mental health leads to bad lifestyle behaviour in socially disadvantaged people - not the other way round, a study suggests.
Binge drinking, smoking, illegal drug use, poor diet and unsafe sex could all be coping strategies for dealing with depression and anxiety, according to psychologists.
The research turns on its head the idea that unhealthy lifestyle might explain high rates of mental health problems among deprived sections of society.
Scientists studied a group of 482 adults receiving care at a sexually transmitted disease clinic in the US.
Patients completed online questionnaires to assess their lifestyle, and were tested for levels of anxiety, depression and perceived stress.
Those with low incomes were more likely to display unhealthy behaviours than those with high incomes, and also had higher rates of mental problems.
The study found that depression, anxiety and stress tended to herald unhealthy behaviour. In contrast, unhealthy behaviour did not predict poor mental health.
The findings, published in the journal Translational Behavioural Medicine, suggest that unhealthy behaviour follows mental conditions but does not necessarily give rise to them.
Dr Jennifer Walsh, from the Miriam Hospital, in Providence, Rhode Island, and colleagues wrote: "Clinicians and practitioners should recognise that there may be high rates of depression, anxiety and stress, as well as health-compromising behaviours, in low income populations, and they should assess mental health as well as these behaviours.''
Offering patients mental health counselling or stress reduction may help them improve their lifestyles, said the researchers.