Depression occurring for the first time late in life could be reflecting a prodromal stage of Alzheimer’s disease, researchers say.

A long-running, large US study found depressive symptoms that occur in both midlife and late life are linked with an increased risk of developing dementia.

The study looked at 13,500 patients in a health maintenance organisation database who were evaluated for depression at 40–55 years and again at a mean age of 81 years.

The researchers looked for diagnoses of dementia over a six–year period, finding more than 3000 (22.5%) of the cohort developed the disease.

At midlife, 14.1% of participants had depressive symptoms, in late life 9.2% had depressive symptoms, and 4.2% had symptoms at both stages.

Adjusting for comorbidities and other factors, the researchers found people experiencing depression in midlife only had a 20% increased risk of dementia, those with late-life depressive symptoms had a 70% increased risk, while the risk of dementia for those with depressive symptoms at both life stages was increased by 80%. In addition, the risk of Alzheimer’s disease was approximately doubled in individuals with depressive symptoms in late life (alone or in combination with midlife symptoms).

“The findings have important public health implications because they raise hope that adequate treatment of depression in midlife may reduce dementia risk, particularly vascular dementia, later in life,” the authors said.

They said the recurrence of depression in late life might be a sign of a long-term process of subclinical cerebrovascular changes that might predispose towards the development of dementia.

“Depression that presents for the first time in late life may reflect the earliest symptoms of dementia, particularly [Alzheimer’s disease] in some individuals,” they wrote.

Arch Gen Psychiatry 2012; 69:493-49

As first appeared in Medical Observer