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Kalsbeek Group

The biological clock

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Health issues such as being overweight, cardiovascular disorders and type-2 diabetes are related to, among other things, the amount of (day)light and the timing of eating and sleeping. Once scientists have figured out the optimum blend of these factors, this may help to minimize the health risks for people with these disorders and for shift workers.

The research of the Kalsbeek research group is focused on those hypothalamic systems that control metabolism, circulation and the immune system. To unravel the mechanisms of hypothalamic integration we study the hypothalamic biological clock and how it enforces its molecular rhythms onto daily physiology and behaviour.


The hypothalamus rules those things in life that really matter, such as sex and food, and love and aggression. This ‘primitive’ area at the base of the brain controls all aspects of our lives that are of the utmost importance, but at the same time mostly go unnoticed. Together the various hypothalamic nuclei control how we respond to stress, injury and infection. They determine our appetites for food and water, and subsequently regulate how we use the energy that we have taken in. The hypothalamus ensures a stable blood pressure, blood volume, electrolyte balance and body temperature. Last but not least, the hypothalamus imposes daily rhythms, such as the sleep/wake rhythm, onto our bodies. In other words, the hypothalamus controls the rhythm of our life. These things might seem mundane compared to the intangible mysteries of cognition, but they are of immediate and profound importance for our health and well-being.

Andries Kalsbeek:

We’ve all heard about ‘the’ biological clock, but it turns out we have more than one.

‘There is a central clock in our brain, which has a direct connection to the retina and which regulates our day/night rhythm. Additionally, we have clocks in our organs, the so-called peripheral clocks. These are ultrasensitive to energy: energy that comes in, i.e., food, and energy that is spent, i.e., by moving around. ‘In the ideal situation, the liver clock receives the signal from the central clock that it is daytime, while at the energy level it receives information that food is being eaten and that the muscles use up energy because they are active. But in our society we also eat and move when it is dark outside. This causes a mismatch, a desynchronization, between the central clock and the peripheral clocks.’

What are the consequences?

‘Your liver ensures that there is always enough glucose in your blood, and your muscles are important for glucose uptake. It is our thinking that when the clocks of the liver and the muscles are out of sync, the liver produces glucose, which the muscles then do not use. This leads to an excess of glucose in your body, which is the start of type 2 diabetes. A similar mismatch occurs with fat metabolism, when the clocks in your fatty tissue get out of sync.’

That is probably also bad news for people who work nights?

‘Indeed, they are more likely to be overweight and to have cardiovascular disorders. They sleep, eat and move at the wrong time, and their central clock also gets confused because of the nighttime exposure to artificial light. Of all these factors, eating at the wrong time has the biggest impact. And its effect is extra detrimental when the food is fatty and rich in sugar.’

Does it make a difference if you sit still or run around order picking for a web shop?

‘In our opinion, shift workers generally should eat as little as possible at night, but whether that also goes for shift workers who are on the go all night? That is exactly what we are currently researching. We are also looking at the rhythm of the shifts. It is our hypothesis that you should work no more than two nights in a row, and then work two or three daytime shifts. If you make sure there are sufficient strong stimuli during the day, your central clock won’t shift. Working nights for longer periods of time increases the chances of your clock shifting. The question is thus how much recovery time you need after a night shift, and how this recovery process is affected by recurrent night shifts.’

What are the effects of computer screen work on sleep?

‘In adolescents we have seen that not looking at a screen in the evening meant they went to sleep earlier and that their melatonin levels began to rise sooner. This effect was even stronger if they wore orange-tinted glasses from about seven p.m. onwards if they did use screens. Quite possibly it is not just the use of a screen that postpones sleep, but also the lighting in the living room and the bedroom.’

So dimming the lights in the evening is a good idea?

‘Yes. The less light at night the better.’

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