Or maybe vice versa. At any rate, the University of Sydney has published findings that demonstrate depression is physiologically really close to jet lag, and both problems seem to involve the cycles of the body’s internal clock:
The study, led by Dr Joanne Carpenter and Professor Ian Hickie from the University of Sydney, is the first to look simultaneously at three key measures of body clock regulation in people with mental ill-health.
“We analysed participants’ core body temperature, cortisol levels and melatonin levels, which we know play important roles in how our bodies manage the circadian rhythm – our 24-hour cycles which regulate things like wakefulness and sleep,” said Dr Carpenter, a Research Fellow at the Faculty of Medicine and Health Central Clinical School and member of the Brain and Mind Centre’s Youth Mental Health and Technology Group.
Melatonin is a hormone that signals to our bodies that it’s time to sleep, while cortisol is a hormone that is found at its highest levels in the morning shortly after waking up. Our body temperature also goes through a daily cycle of rising and falling that is closely aligned with sleep.
“When we looked at these three measures in young people who presented to mental health services, we found that 23 percent of patients were experiencing a kind of physiological jet lag.”
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The study comprised two groups – the first, young people between the ages of 16-35 who presented to mental health clinics in Sydney for treatment; the second, young people who had no prior history of mental illness.
The participants in the two groups were monitored overnight in a chronobiology lab to measure their sleep and body clock related hormones in the lead up to sleep and in the hours after they woke up. Their body temperatures were recorded continuously using a sensor that was swallowed by participants.
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“We were able to measure melatonin and cortisol levels using saliva samples in the lead up to sleep and after participants woke, which is the first time these key markers of the circadian rhythm have been combined with body temperature to study how circadian rhythms might be misaligned in people with mood disorders,” says Dr Carpenter.
“We found that 23 percent of patients had at least two of these circadian rhythm measures out of sync with each other. This is similar to the disruption we see when travelling across time zones or undertaking shift work, when the body clock becomes out of sync with the external environment. However, what we are seeing here is circadian rhythms being out of sync with each other within a person’s body, a kind of ‘internal jet lag’.
“While we do see teenagers sleeping later because of normal developmental shifts in the body clock to later timing across adolescence, what we are seeing here is a more extreme kind of circadian disruption where the clocks are not just delayed but not lining up with each other.”
“We also found a correlation between how out of sync patient’s body clocks were and the severity of their depressive symptoms,” said [co-author] Dr [Jacob] Crouse. “In particular, higher depressive symptoms were linked to core body temperature cycles that were running on an earlier clock than other rhythms and sleep-wake patterns.”