Stress Interferes With the Rhythm of Life: Why This Matters
Disrupting daily rhythms has serious consequences for the brain.
Posted March 16, 2016
The whole of life is locked into a rhythm. A slow-motion camera focused on any road would reveal two surges in traffic: one in the morning, the other in the evening. We call them rush hours, but they are really a reflection of the way that our lives are organized. Underlying this is the way we alternate periods of sleep and wakefulness. This, in turn, is closely linked to the occurrence of day and night.
Anyone who travels knows the effects of disturbing these rhythms. Jet-lag stops you sleeping when you should, alters your mood and interpersonal relations, makes it difficult to think clearly and effectively, and generally degrades the quality of life. But only for a few days: luckily, we recover, and go back to our usual ways. Were it to last for, say, several weeks, our lives would be disrupted and we would almost certainly seek medical advice.
Body rhythms are controlled by a clock in the brain, called the SCN (suprachiasmatic nucleus). It lies just behind the eyes, which reflects the fact that light controls it. Left to itself, it would generate a rhythm that would be approximately, but not accurately, 24 hours: so it’s a self sustaining clock – it doesn’t an external stimulus to keep it going. Light from the eyes synchronizes it to the external day-night rhythm so that the body clock now ticks at exactly 24 hours. One of the important functions of the SCN clock is to generate a daily rhythm of cortisol, the hormone from the adrenals.
Cortisol is normally at its highest early in the morning, and gradually drops to quite low levels in the evening, rising again during the later part of the night. The cortisol rhythm has an essential function: it synchronizes many of the clocks in other parts of the body, so they all adopt a 24 hour rhythm though, importantly, they have different peaks and troughs relative to the time of day. So your body prepares itself for the various events, themselves usually periodic, that can happen as each day passes – for example, mealtimes.
Stress can disrupt the usual daily pattern of cortisol. This is particularly likely to happen if the stress is persistent, unpleasant, threatening and difficult to predict or control. Cortisol levels may be raised, and the usual decrease as the day progresses may be blunted. This alters the signal to the rest of the body. Disruption of these bodily rhythms, and their desynchronization from each other, is why jet-lag is so unpleasant. The reason you recover is because your SCN clock, after a few days, resets to the new light-dark cycle and gathers them together again. But persistent stress, because it interferes with the daily pattern of cortisol, results is a more long-standing disturbance of these clocks, so the body and the brain - parts of which also contain secondary clocks - begin to malfunction.
A certain amount and type of stress is beneficial. Life without some demands, surprises or challenges would be very dull indeed. But there is a threshold, above which stress becomes harmful. It may be the amount, the nature, or the way the individual perceives it. It certainly varies between individuals: an event that some regard as an exciting challenge might be viewed as a dangerous threat by others. Experience, genetic make-up, social networks, possession of assets or resources – they all contribute to what is seen as stressful and how the body responds. Many studies show that the onset of mental illness such as depression or schizophrenia is associated with previous or current severe stress, or ‘life events’ as they are sometimes called.
More and more attention is being paid to the idea that disruption of the body’s rhythms, largely through disturbance in the daily rhythm of cortisol, might be responsible. There is growing evidence that abnormal patterns of cortisol can damage the brain. It alters the activity of genes that we know are important for brain function. It accentuates the damaging actions of other events – for example, traumatic brain damage or a stroke. It can even predispose the brain to inflammation, which is being increasingly identified as an important element of several disorders of the brain. Yes, the rhythm of life really is a powerful beat. It may put a tingle in your fingers or a tingle in your feet, but if it’s disturbed, it can endanger the brain. You need to dance to the music of time.
Credit: Sunrise photo by ssguy/Shutterstock