Researchers suggested that negative relationships might make someone more likely to drink and smoke, which increases their chances of developing dementia.

"Annoying" relatives can increase your chance of developing dementia, a new study has found.

The 10-year study by researchers from four British universities found that the stress of having relatives who were "critical, unreliable and annoying" makes people more likely to develop the disease.

Researchers suggested that negative relationships might make someone more likely to drink and smoke, which increases their chances of developing dementia.

Previous studies have shown that having a support network keeps older people mentally healthy for longer, but this is the first time poor-quality relationships have been found to have a negative impact.

Dr Mizanur Khondoker, a senior lecturer in medical statistics at UEA’s Norwich Medical School, said: “A relationship or social connection that does not work well can be a source of intense interpersonal stress, which may have a negative impact on both physical and mental health of older adults.

"It is not only the quantity of social connections, but the quality of those connections which may be an important factor affecting older people’s cognitive health."

More than 10,000 participants were asked questions such as "How much do they criticise you?" and "How much do they get on your nerves?" about family members, rating their answers on a scale of one to four.

An increase of one point on the "negative support scale" meant their risk of developing dementia was up to 31 per cent higher.

The study was led by researchers from London Metropolitan University, UCL, Nottingham University and the University of East Anglia.

Dr Khondoker said that the findings could help prevent dementia by "raising public awareness of the importance of having a positive and supportive relationship with older adults".

Researchers added that the findings could help carers identify risk factors for dementia among patients who have poor-quality social relationships.

Professor Andrew Steptoe, professor of psychology at UCL, said: “Our findings add to the growing evidence of the relevance of social relationships for cognitive health in older age.

"Specifically for health and social care practice, the research highlights the value of thinking about social relationship issues in individuals vulnerable to dementia, while pointing toward specific ways of potentially modifying risk."

Poor-quality relationships have previously been associated with higher levels of inflammation, which is linked to dementia.

Telegraph.co.uk