"Annoying" relations can increase your chance of developing dementia, research has found.

The 10-year study by a team from four British universities found that the stress caused by family members who were "critical, unreliable and annoying" makes people more likely to fall victim to the disease.

Previous research has 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 the University of East Anglia, 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."

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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, and asked to rate 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.

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

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

Meanwhile, having family members who were reliable and understanding reduced the chance of developing the condition by up to 17 per cent, the study found.

This was particularly the case where the older person was interacting with children. Studies have also shown that interacting with children can make older people less likely to develop depression, which is associated with dementia.