When the internal clock gets out of sync

For millennia, daylight was the most important factor that synchronised the inner clock with the day-night rhythm. Under natural conditions, the day is thus the time for physical activity and the night is the time for sleep and regeneration.

In the modern world, life is increasingly disconnected from the day-night rhythm. The ubiquity of electric light, long distance travel across time zones and shift work contributes to the inner clock having to adjust at short intervals. Deviations between the day-night alternation and the inner clock are noticeable, for example in short-term jet-lag after long flights. In the long term, by contrast, disturbances to the Circadian rhythm negatively affect bodily functions and endanger physical and mental health. They can compromise sleep duration and quality, change eating habits and lead to hormonal changes and impairments to the body’s energy metabolism. Thus, these changes encourage the onset of obesity, heart/circulatory diseases and Type 2 diabetes.

Investigations have shown that long-term shift and night work increases the risk of chronic diseases and shortens life expectancy by years. This work pattern causes physical activity, nutrient intake and rest periods to fall at unphysiological times. These deviations from the inner clock encourage disturbances to the metabolism, thus, it was shown in the study that shift-workers suffer twice as frequently from metabolic syndrome. This is the name given to a combination of disturbed carbohydrate and fat metabolism, arterial hypertension and upper-body obesity, which encourage consequential diseases of the heart-circulatory system and type 2 diabetes.

Furthermore, the sleep rhythm plays a central role in general health. If the duration of sleep falls, the risk of chronic physical and psychological illnesses increase. Sleep deprivation has also been proven to encourage weight gain. A daily sleep duration of less than six hours increases the occurrence of obesity by up to 60%, by comparison of six to seven hours. Various factors come under consideration as the cause of this. Lack of sleep influences blood levels for the hunger promoting hormone ghrelin and the anorexigenic hormone leptin. It also increases the activity in the area of the brain associated with reward and a craving for tasty, calorie-rich foods.

Chronic sleep deprivation and a shift in nutrient intake also leads to a reduced demand of the body cells for insulin and thus encourages the onset of type 2 diabetes. For a normal sleep duration of less than 5 hours, the risk of diabetes increases by over 50%. Along with glucose metabolism, disturbances to the Circadian rhythm and lack of sleep also impairs fat metabolism and leads to increased blood fat levels and an adverse shift in cholesterol levels, in the sense of higher LDL and lower HDL cholesterol ratios. This combination of sugar and fat metabolism disturbances is in turn an important risk factor for the development of heart-circulation diseases, and so increases the risk of heart attacks and strokes.

Work and lifestyle can intervene with the body’s inner clock and therefore exert a more extensive influence on health. This primarily affects people who have been working nights and shifts for more than ten years. When the body is in its younger years it still has enough resources to balance out disturbances to the Circadian rhythm, however this capacity steadily reduces with increasing age. A regulated daily routine should be aimed for in the long term. If this is not possible due to work schedules, measures should be taken to promote the metabolic health of the body. This includes, most of all, a healthy and balanced diet and regular physical activity. Choosing to consume low-fat and low-calorie foods during night shifts is also recommended.

Sleep hygiene also plays a crucial role. Enough sleep in quantity and quality should be regarded as an important constituent of maintaining health. A daily sleep routine that guarantees at least seven to eight hours of undisturbed sleep should be established.

Although the demands of modern work deviate ever further from human physiology, small changes in behaviour can have large impacts on health in the long term, countering the negative effects of an unphysiological working life.

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