Dementia affects women in the later stages of life much more than men of the same age, a study has shown.
Scientists in the US found that 45% of women from a group of 911 people aged 90 or older had dementia compared with 28% of men.
Previous evidence has shown that dementia prevalence for both men and women increases between the ages of 65 and 85.
Less than 2% of 65 to 69-year-olds suffer from dementia, but the proportion increases to 5% for 75 to 79-year-olds, and more than 20% for 85 to 89-year-olds, the research published in the journal Neurology found.
Research from the University of California found that the likelihood of having dementia doubled every five years for women after the age of 90, but not for men.
Women with a higher education were up to 45% less likely to develop dementia than those who were not so well educated.
Epidemiologist Dr Maria Corrada said: "Our findings show that more will need to be done to provide adequate resources to care for the increasing number of very old people with dementia."