Disturbing Our Sleep With Shift Work

Most of us only have our sleep disturbed when we get jet lagged or start working shifts at really odd hours. To find out how this affects us, Priya Crosby spoke to Michael Hastings from the MRC Laboratory of Molecular Biology in Cambridge who works on understanding our 'body clocks' or circadian rhythms.

Priya - So, we all get tired if we're suddenly asked to do a night shift, but people who do it regularly seem to adapt to these strange alternate hours. Can you tell us, how do our bodies accept this new kind of timing.

Michael - Well, you mentioned it yourself in the introduction that we have a clock in our body. In fact, we have probably innumerable clocks in our body. There's principal clock in the hypothalamus, something that Jason mentioned earlier which is called the suprachiasmatic nuclei. That is basically the conductor to a whole orchestra of other clocks spread right across the body. So, there are clocks in the liver, there are clocks in the stomach, the immune system, you name it, it's all rhythmic, and nature programme us to operate on a normal 24-hour day. That 24-hour day because the suprachiasmatic nuclei are connected to the retina of the eye, they know as it were when it's day and when it's night, and then they can relay that information to all of the other body clocks right across our body.

Of course, the problem arises is that nature never intended us to jump on airplanes and travel across time zones. So that when we do that, in fact, the capacity of our body clock system to adjust to a change in the light dark cycle is very limited. At the time we're trying to catch up with the changing light dark cycle, this beautiful programme that normally controls our physiology and behaviour is completely scrambled and that's why we feel lousy and we're confused, and we can't concentrate.

Priya - How long does it take our body, roughly, to adapt to this new cycle?

Michael - Yes, so the rule of thumb and you can demonstrate this in people, you can also demonstrate it in experimental animals. The rule of thumb is that for every hour difference in time zone, it takes about one day to readjust. So, you know when the clocks go forward or back in spring and autumn, that's a one hour difference, so it's not too much of a problem for people. But of course if I were to fly from here to New York, it's a 5-hour time zone difference. It would probably take 5 days for me to adjust to New York time and then when I come back, I've got another 5 days of readjustment to Cambridge time.

Priya - So, it's quite a long time to shift between these two cycles. Are there any problems, perhaps not so much with jet lag which is quite rare, but if someone shifts a lot, for example if they're doing shift work and they change between working days, and nights, would there be problems with doing that kind of thing?

Michael - Absolutely. I'm sure that many of listeners have work shifts or have experienced it. It's not a pleasant thing to do. From the point of view of the body clock, we can have animals for example and change their light dark schedules and mimic the effects of shift work. And if for example, you have let's say a mouse, which is a type of mouse which has got problems with its heart, if you then mimic shift work changes on the light dark cycle, that will aggravate the cardiovascular disease that we see experimentally.

You can then jump from those experimental observations to look at people, and if you do epidemiological studies, so you look across a large number of people trying to correct for all the different potential confounding factors, one finds that people who have had a working life on rotating shift work. So, they are forever trying to jump from one clock zone to another, they've got a let's say 20% increased chance of getting certain forms of cancer or indeed cardiovascular disease. So, there is a real life cost to people, trying to work against their natural body rhythm.

Priya - We've got a question in from one of our listeners here from Anthony Gortastic. He says that he's a shift worker. Every 21 days, he does 7 nights and he wants to know what's the best thing to do eating wise. Should he eat meals through the night as if it were a day or should he just have lots of light snacks?

Michael - I mentioned there's a clock in the liver and that controls when the liver produces the various digestive enzymes. The clock in the liver is actually responsive to meal times. In an experimental animal, if you change a time when they can eat, you see that their rest activity, their sleep wake cycle stays the same, but the clock in the liver gets pushed out of sync with it. So, meal times are very potent stimulus for this internal synchronisation.

In terms of what your listener says, given that he's spending most of his time - if it's 7 days out of 21 and you've got 14 days out of 21 on normal schedules. So, I think the best thing - my personal view would be, it's better for him when he on the shift to stick to the meal times he has when he's not on a shift, to stick to his normal routine rather than trying to change things for 7 days and then have to change them back again after 7 days.