A study that took place over the course of 17 years discovered that out of 1,000 elderly people 22% of those that were depressed at the beginning of the study later developed dementia, compared to 17% of those who developed dementia but were not depressed.
However, the study results do not mean that depression is the cause of dementia, and the actual association between the two diseases is not immediately clear. It is still unclear if depression is an actual risk factor, or if it simply may be an early sign of impending cognitive decline. It also potentially could be that changes in the brain are present in both conditions.
Lifestyle factors were also not measured in the study including social interaction, poor diet, and lack of physical activity all of which may increase the risk of dementia and depression. It is also important to note that this study looked at elderly people with an average age of 79 years, which does not clearly link to depression that begins earlier on in life.
The study was performed by researchers from Boston University and the University of Massachusetts both in the United States and was funded by many US medical institutes.
The study mentioned previously began in 1990 with 1,166 study participants out of which 949 were determined to be dementia free at the time of the studies’ beginning.