For young people, there are three critical pathways to depression. Understanding them opens the door on early diagnosis and intervention.
Clinical Depression is a life-threatening illness. However, unlike other high-profile diseases, there is no coordinated national campaign aimed at early intervention or prevention.
Professor Ian Hickie, Director of the Brain & Mind Research Institute, likes to draw the analogy with the pathways to heart disease. We know that smoking, lack of exercise and high blood fats are risk factors for heart disease, so we attempt to modify those risks in the hope of preventing premature death or heart failure 30 years down the track. We don’t wait for a first heart attack to happen before providing effective interventions. He believes that a similar tack needs to be taken with clinical depression. But to do so, it’s necessary to identify the earlier forms of depression that may lead to premature death or disability.
Consequently, he has shifted his focus from looking at those middle-aged people with chronic illnesses who frequently present to specialist mood disorder clinics. That’s just too late for early intervention or prevention. “Traditionally, we have used the experiences of 30- to 50-year-olds to characterise our diagnostic tools for depression. The area is dominated by this model and there is a great deal of frustration in the way these patients with chronic disorders often respond poorly to psychological or pharmacological therapies,” says Hickie.
People come to clinical depression in mid-life by many different roads. There are two major onset times for depression, adolescence and old age, and both have very different causes. The latter affects those over 70 years of age and is caused by changes in the brain due to small vessel vascular disease. Genetics and the environment are far less relevant to late-onset depression. By contrast, teenage depression typically begins after puberty and continues to become more common into the early 30s.
Hickie believes that the years between 11 and 15 are critical for first diagnosing depressive tendencies. That’s because the years after puberty see the transition from childhood anxiety and other developmental risks to more adult-like depressive disorders. The brain drives puberty and the hormones that are released feedback on the brain and behaviour. Other critical changes, like those related to the sleep-wake cycle, also happen during this period.
So what are the pathways to depression which are identifiable in childhood or adolescence and what are their complications? Hickie says there are three critical pathways:
Children with learning difficulties and high impulsivity, such as boys with ADHD, or children who have experienced problems with brain development, are at increased risk of psychiatric disorders, including depression. They lose opportunities at school and in employment, and may even end up in juvenile justice institutions.
This is the most common route to clinical depression. More than 50 percent of depressed teenagers have had childhood anxiety. As anxiety in children is a general phenomenon, that’s perhaps not surprising.
The brain becomes over-sensitive to environmental threats and the child becomes fearful and unable to deal with their situation, leading to an anxious type of depression. In teenagers and adults, social anxiety becomes quickly associated with alcohol and substance abuse, particularly in boys. Added to depression, there is the increased risk of premature death from heart disease. “More than 50 percent of depressed teenagers have had childhood anxiety...”
There are strong links between circadian (i.e. the 24 hour sleep-wake cycle) disturbance and some of the characteristic symptoms of depression, including delayed sleep onset, oversleeping, overeating and daytime fatigue. The childhood precursors to depression based on circadian disorders may overlap with ADHD symptoms or other developmental problems. These children are often natural night-owls and have poor sleep patterns. They can be up all night on the internet and they get little physical activity.
The circadian-disorder pathway to adolescent depression is less well-known, but it is here that Hickie believes successful prevention and early intervention are most likely to be achieved. “Restoration of normal sleep-wake cycles is increasingly thought to be a marker of effectiveness for antidepressant treatments. Failure to restore normal rhythms is highly predictive of ongoing symptoms or early relapse,” says Hickie.
Interestingly, drug treatments for major depression have often worked on increasing serotonin, having the effect of disrupting slow-wave and REM sleep which is at odds with normalising circadian rhythms. Instead, new behavioural or drug regimes focus on re-synchronising circadian rhythms. The natural sleep hormone melatonin is already widely used in the community and new antidepressants have been developed based on this principle.
"More than 50% of depressed teenagers have had childhood anxiety..."
Hickie describes the circadian-based systems in humans as an example of ‘unintelligent design’. “There are different clocks in the body – they are all running to different times! We rely on the master clock in the brain to get us back into synchrony and feeling energetic and well. The timing of the master clock is set by light exposure and physical activity. If it is working well, it controls all the other clocks in the body so you can feel well and function properly. However, the clocks are clearly dysfunctional in people with major mood disorders.
“We have a whole lot more objective tests, particularly for circadian rhythm, and Sydney University has real strength in these areas. The Woolcock Institute has led the nation in sleep and circadian research. Working with the George Institute, we’ve discovered that if your child sleeps short, they are more at risk of onset of depression as a teenager, so developing good sleep/wake patterns in childhood is important. When the circadian cycle is off, you are more likely to get fat and suffer from diabetes,” says Hickie.
Ironically, ensuring we get good sleep is all about what we do during the day. We have to maximise physical activity and sunlight exposure, and the best time to do that is in the morning. Melatonin is turned off in the morning and the critical timing of the circadian rhythm is then set for the day. So having children in classrooms all day working at computer screens is not helping the problem. “The way the school day is structured is important. We should be running the academic component later in the day. The preoccupation of schools is with academic outcomes, but if you want brighter students, they need to be outside exercising. It’s a nonsense idea sitting in a library or classroom all day.”
While young children go to bed early and rise early, in normal development there is typically a shift so that teenagers start going to bed later and getting up later. In the US, some schools have adapted to take account of this, starting classes later and allowing students to get a good sleep. Not so in Australia, where the school timetable is more rigid and additional classes are often scheduled before the normal school day begins.
Hickie believes we can potentially prevent the onset of adolescent depression if we treat the causes in context, providing the right type of intervention at the right point in time. “Twin studies have shown us that the risk of depression is 30 to 40 percent genetic, and 50 to 60 percent environmental. In other words, the environment is twice as important as genes in determining whether a child will become depressed. That means we have considerable opportunity to reduce the burden of depression through early intervention and prevention.”
This optimism is particularly important in light of the consistent and unexplained trend over the past 50 years of an increase in depression in younger people. Hickie believes that changes in our social structures which have resulted in less supportive families and communities might be part of the problem. “We have to provide new ways to support our young people. We are not going back to the 1950s and relying simply on community, church and youth groups, or women staying at home.” He thinks that technology might provide a solution through the Internet. “We have to come up with smarter ways collectively to make sure that happens, especially for those at greatest risk.”
Ian Hickie AM is Professor of Psychiatry, Sydney Medical School and Director of the Brain & Mind Research Institute.