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Just why does homelessness cause premature ageing?

Homelessness has become a national crisis in Ireland, with the numbers of homeless people in Ireland having doubled in the past four years. The difficulties of daily living are obvious for this group, but what is less well known is that homelessness is also related to the rate at which people age. Clinical evidence has found homeless people in their forties and fifties with conditions such as osteoporosis and dementia that are usually seen in people in their seventies or eighties.

Dr Clíona Ní Cheallaigh is conducting a study on Premature Ageing in Long-term Homeless Adults in Dublin (the PATH study), funded by the Health Research Board, the Royal City of Dublin Hospital Trust and the Global Brain Health Institute

Heightened levels of childhood and adulthood abuse and trauma mean the homeless have greatly increased levels of psychosocial stress. However, just how this trauma affects our biology is a burning but unanswered question.

The first phase of the study will measure the degree of physical and cognitive frailty in homeless people versus a control group from the Irish Longitudinal Study on Ageing (TILDA).

Evidence shows that chronic inflammation, such as that seen in people with rheumatoid arthritis, leads to premature ageing, memory loss and depression; and, also, that when animals are under social stress their white blood cells show increased inflammation. The second phase of the study will test the hypothesis that the childhood trauma and stress that homeless people live with causes increased inflammatory responses, and that this causes them to age more rapidly. This will be the first human study to look at the effects of psychosocial stress on responses in innate immune cells.

The third phase of the study, funded by the Global Brain Health Institute (GBHI), will look at the effect of homelessness and inflammation on the brain. The brain is the key link between people’s life experiences and their behaviour, and homelessness may be affecting the structure and function of the blood-brain barrier and the brain.

Understanding premature ageing in homelessness will give us insight into the mechanisms via which social exclusion gets “under the skin” to precipitate illness and earlier ageing and will inform policies to deliver improved health equity.

Prof Clíona Ní Cheallaigh said

“Premature ageing in homeless people is poorly understood. We are delighted that the Health Research Board, the Royal City of Dublin Hospital Trust and GBHI have given us funding to look at the effect of homelessness on health. This study will contribute to a paradigm-shift in the understanding of how adversity and exclusion affect health and will inform national and international health and social care policies, contribute to reducing stigma and improving health equity.”

About Prof Clíona Ní Cheallaigh

Prof Clíona Ní Cheallaigh is a Consultant Physician in General Medicine and Infectious Diseases in St. James Hospital and Associate Professor in Clinical Medicine in Trinity College, Dublin. Her clinical and research interests centre on understanding and addressing the effects of social exclusion on health.

She has established and leads the first hospital-based Inclusion Health Service internationally (, ( This service has demonstrated the value of directly addressing social exclusion to patients and to the health system. The Inclusion Health Service has recently received funding through the Service Reform Fund to carry out a pilot Homeless Hospital Discharge programme. The Inclusion Health Service has been extensively covered in national television, radio and print media.

She completed her specialist Academic Fellow training in infectious diseases and internal medicine in 2016. She is a firm believer in the critical value of research in shaping health and social policy. Her PhD resulted in numerous published works which includes a first author paper in the high impact journal Immunity. She is currently supervising two PhD students (one studying accelerated ageing in people living with HIV and one studying socially excluded people’ access to healthcare). Her focus is on identifying the mechanisms through which psychosocial stress causes immune activation and through which low-grade chronic inflammation affects health and aging.

Prof Ní Cheallaigh combines a deep commitment to health equity with the scientific expertise needed to deliver this ambitious and innovative project. She is currently establishing an independent research group based in the Department of Clinical Medicine in Trinity College, Dublin and has access to the excellent facilities, supports and mentoring in the School of Medicine in TCD.

About TCD School of Medicine

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