Depression symptoms that steadily increase in
older adults are more strongly linked to dementia than any other types
of depression, and may indicate the early stages of the disease,
according to the first ever long-term study to examine the link between
dementia and the course of depression, published in The Lancet Psychiatry journal.
Symptoms of depression are common in people with dementia, but
previous studies have often looked at single episodes of depression,
failing to take into account how depression develops over time. The
course of depression varies greatly between individuals -- some might
experience depressive symptoms only transiently, followed by full
remission, others might have remitting and relapsing depression, and
some might be chronically depressed. Different courses of depression may
reflect different underlying causes, and might be linked to different
risks of dementia.
The study included 3325 adults aged 55 and over, who all had symptoms
of depression but no symptoms of dementia at the start of the study.
The data was gathered from the Rotterdam Study, a population-based
cohort study of various diseases in the Netherlands which allowed the
authors to track depressive symptoms over 11 years and the risk of
dementia for a subsequent 10 years.
Using the Center for Epidemiology Depression Scale (CES-D) and the
Hospital Anxiety and Depression Scale-Depression (HADS-D), the authors
identified five different trajectories of depressive symptoms -- low
depression symptoms (2441 participants); initially high symptoms that
decreased (369); low starting scores that increased then remitted (170);
initially low symptoms that increased (255); and constantly high
symptoms (90).
Of the 3325 participants, 434 developed dementia, including 348 cases
of Alzheimer's disease. Among the group with low symptoms of
depression, 10% (226/2174) developed dementia. The researchers used this
as the benchmark against which to compare other trajectories of
depression -- the study did not compare the risk of dementia following
depression with the risk of dementia for adults in the general
population (without depression).
Only the group whose symptoms of depression increased over time was
at an increased risk of dementia- 22% of people (55/255) in this group
developed dementia. This risk was particularly pronounced after the
first 3 years. Individuals with remitting symptoms of depression were
not at an increased risk of dementia compared to individuals with low
depressive symptoms. The authors say that this suggests that having
severe symptoms of depression at one point in time does not necessarily
have any lasting influence on the risk of dementia.
The authors say their findings support the hypothesis that increasing
symptoms of depression in older age could potentially represent an
early stage of dementia. They also say that the findings support
previous suggestions that dementia and some forms of depression may be
symptoms of a common cause. They say that at the molecular levels, the
biological mechanisms of depression and neurodegenerative diseases
overlap considerably including the loss of ability to create new
neurons, increased cell death and immune system dysregulation.
According to Dr M Arfan Ikram, Department of Epidemiology, Erasmus
University Medical Center, Rotterdam, Netherlands, "Depressive symptoms
that gradually increase over time appear to better predict dementia
later in life than other trajectories of depressive symptoms such as
high and remitting, in this study. There are a number of potential
explanations, including that depression and dementia may both be
symptoms of a common underlying cause, or that increasing depressive
symptoms are on the starting end of a dementia continuum in older
adults. More research is needed to examine this association, and to
investigate the potential to use ongoing assessments of depressive
symptoms to identify older adults at increased risk of dementia."
Writing in a linked Comment, Dr Simone Reppermund from the Department
of Developmental Disability and Centre for Healthy Brain Ageing at the
University of New South Wales, Sydney, Australia, says: "In conclusion,
several factors can contribute to the development of both depression and
dementia. The questions are if, and how, the presence of depression
modifies the risk for dementia. The study by Mirza and colleagues
provides an answer to the first question: depression, especially
steadily increasing depressive symptoms, seems to increase the risk for
dementia. However, the question of how the presence of depressive
symptoms modifies the risk of dementia still remains. More studies of
depression trajectories over a long period, with inclusion of biological
measures, are necessary to understand the link between depression and
dementia, in particular the underlying mechanisms. A focus on lifestyle
factors such as physical activity and social networks, and biological
risk factors such as vascular disease, neuroinflammation, high
concentrations of stress hormones, and neuropathological changes, might
bring new treatment and prevention strategies a step closer."
Source: https://www.sciencedaily.com/releases/2016/04/160429192926.htm
