It's not uncommon for older people - especially those who live alone - to feel sad. But when that sadness becomes clinical depression, the risk of dementia may be higher, scientists say.
A study by researchers at the University of California San Francisco found that the risk of Alzheimer's disease doubled for people who were depressed in later life and the risk of vascular dementia more than tripled when the depressed people were midlifers.
The researchers looked at the medical histories of 13,535 Californians. They found that more than 72 percent of the participants had no depressive symptoms. Another 14 percent suffered from depression in midlife, more than 9 percent had symptoms in later life and about 4 percent were depressed both at midlife and in later life.
Only 20 percent of those with no history of depression developed dementia while 23 percent of those with midlife symptoms and 31 percent of those with late life symptoms developed dementia. About 31 percent of those who had depression at both mid and late life developed dementia.
It's not clear from this study whether the depression itself may be a symptom of dementia but the research does suggest that midlife and older people who experience depression should be treated.