Now for the science bit: Prof. Russell Foster on light and the body clock
Prof. Russell Foster has been on Radio 4’s ‘The Life Scientific’ programme talking about his favourite subjects: circadian rhythms and how light affects the body clock. In the half-hour slot he spoke about the breakthrough moments in his research career, the effects on our health when we fight against our body clock’s natural rhythm and the implications for healthcare now that we know the eye has a third type of photoreceptor – one that detects brightness.
If this sounds a bit heavy-going, it isn’t. Prof. Foster uses lots of examples from nature, his animal research and findings from groups of people with blindness that help to illustrate how the various receptors work and how light is fundamental to our body clock so it’s well worth a listen.
He introduced the subject by explaining that although we have the 21st century option of a 24-hour lifestyle, our body clocks have millions of years of training that tells them ‘light equals daytime’ and this means we're not going to adapt overnight!
He used night-shift workers as an example: people assume that after a few weeks shift workers would have adjusted to their routine but they don’t. Working in a relatively dim environment then being exposed to brighter light on the way home and during the day will always re-set their body clock.
All animal life – right down to single-celled organisms – has some kind of body clock. Birds were known to have specialised photoreceptors to measure the length of daylight; the days getting shorter or longer tell their body clock what time of year it is so that biological processes, such as laying eggs, are in sync with their environment.
But mammals seemed only to have rods and cones, the light sensors that capture different wavelengths and are responsible for vision and detecting colour. So how did they tell the time?
Mice provided the first clues. Foster noticed that old mice with degenerative eyesight no longer maintained normal sleep/wake patterns and their body clock was obviously drifting. On the other hand, follow-up research showed that blind mice (those without rods and cones) did still manage to keep internal time. He decided that there must be a third photoreceptor in the eye, a ‘brightness detector’.
Further studies involving totally blind patients backed this up, since they still had normal rest/activity cycles, going to bed and getting up at normal times of the day.
He finished off by talking about the impact this has had on healthcare. For example, macular degeneration can often lead to a disrupted body clock as we get older and this has led to the introduction of better and brighter lighting in care homes. And it's now recognised that cataract operations to improve vision often have the added benefit of stabilising the patient’s sleep/wake cycle, since removing the cloudy lens allows more light through.
You can still listen to the whole interview on the Radio 4 website.
If you’re interested in finding out more about circadian and seasonal rhythms, you can buy Prof. Russell Foster’s book.