Previous studies have shown that in men and women over the age of 65 the prevalence of dementia increases by 5% and doubles every 5 years thereafter.  However, no studies have specifically analysed the 90+ category to find out if the prevalence of dementia kept on increasing at this alarming rate or if it reached a plateau.

This study revealed that the prevalence of dementia kept on doubling in women aged over 90 but not in men of the same age.  It allows us to look at the risk factors associated with dementia and whether they have a greater effect in women aged 90+ or if certain sex-specific risk factors are the cause.

Rebecca Wood, Chief Executive of the Alzheimer's Research Trust said:  "This is a large study with interesting results.  There may be a hormonal link to explain the difference between the incidence of dementia in men and women after the age of 90.

Previous research has shown that testosterone in men appears to be protective and has positive effects on mood and thinking skills, while a number of studies have shown that low levels of oestrogen during menopause increase a women’s risk of Alzheimer’s.

Further research is needed to investigate whether it is a hormonal link or a combination of other factors that are the reason for this difference between men and women. A better understanding of the causes of Alzheimer’s could lead scientists to new ways to cure this devastating disease.

This is an important area of research with dementia affecting 450,000 women in the UK - approximately two women are affected for every man."

This study also found that women with higher education were less likely to develop dementia.  This may be because women who were educated at this time were usually of higher socioeconomic status and thus would have had better living conditions and diets or it may be that as a result of increased education, aspects of the brain's structure and function act to buffer the effects of the changes that occur in the brain at the onset of dementia.