Good things happen as we get older. We start to have grandchildren and great grandchildren. We celebrate our 80th birthdays and 60th wedding anniversaries. Growing old doesn’t mean inevitable depression from the events we might associate with hitting our 80s: ill health, isolation, or widowhood.
But in developed parts of the world, the over-85s population is the fastest growing age group. And while it is made up of individuals of different physical and mental health status, old age also brings frequent and severe physical and social losses that can induce a higher level of depressive symptoms.
Our recent research, published in Research in Human Development, looks at the impact of cortisol, the stress hormone, in older people over the age of 85. We found that depressive symptoms from the age of 65 had a cumulative effect on the level of cortisol in the body 20 years later.
Using data from the Australian Longitudinal Study of Ageing, we found that on average, depressive symptoms increased from age 65 onwards – results that are similar to those from a 2001 Danish study. It indicates that as we get older it may become increasingly difficult to cope with the challenges we face in very old age.
Cortisol is released by the body in response to stress. This increases blood sugar levels and suppresses the immune system, which helps the body to survive immediate threats, or prepare for the exertion of a new day. While prolonged cortisol secretion, which may be due to chronic stress, could have significant negative effects on the body in the long term, including chronic fatigue and cardiovascular diseases, certain amounts of it play a good part in our lives.
The daily stress cycle
Most studies on cortisol in old age so far have examined aggregate levels of cortisol in people through the day - looking at average daily amount for example. Our research looks at all the separate components, including the wake-up level, cortisol awakening response (CAR), in a group of participants with a mean age of 89.
The release of cortisol shows a regular daily cycle in the average person. The cortisol cycle has a characteristic shape, with relatively low levels when we wake up and a peak about 30 minutes later. The increase after waking is termed the cortisol awakening response (CAR) and although a definitive function isn’t currently known, it is speculated that it plays a critical role in mobilising energy at the start of the day, enabling individuals to respond to the forthcoming challenges and demands of the day.
After this first peak when we wake, cortisol then gradually declines through the day until bedtime. CAR can vary, based on many factors including the quality of our sleep, our age, or chronic health problems, but the average increase is about 50%.
Our study combined data from research over a 15-year period, from 1992 to 2007, with data from a shorter, one-week period in 2010, where we charted the cortisol pattern.
We found that participants with more depressive symptoms over the 15 years showed a significantly lower CAR when they woke in the morning. This association between higher past depressive symptoms and lower CAR may inform research on burnout and fatigue, that is, lack of energy, associated with chronic stress.
In contrast, CAR is not linked to current depressive symptoms, which were measured in 2010 when participants were in their 80s. This means that depressive symptoms contribute to a fall in CAR over a prolonged period.
These results have significant clinical and policy implications. It means that depression in old age could and should be attended to and treated early on, before the negative effect of it accumulates and exerts further impact to physical health.
The link between depression and ill health in very old age is complex. Depression in very old age involves the interplay of multiple factors including cognitive functioning, physical health, and social support. Our research suggests that depression in very old age isn’t just a sudden inability to cope with a specific event. Interventions can be implemented to improve emotional well-being and potentially enhance longevity in older adults.