Clocks are about to change. Our body clocks turn out to be key to making medicine work

Dr Muiris Houston: As the clocks spring forward, we would be wise to look at chronotherapy and the link between time and drugs

Chronotherapy in oncology treatment involves syncing the time at which cancer drugs are administered with a patient’s natural circadian rhythm with the aim of minimising side-effects while maximising the effectiveness of the drug.

As our clocks change to daylight saving time next weekend, a global reticence to finally do away with our biannual changing of time persists. The European Union, the United States and individual provinces in Canada have plans in place, but no one seems ready to trigger the starting gun.

But a US Bill to authorise a permanent change to daylight saving time that has been repeatedly thwarted is back in play. Last week, US senator Marco Rubio reintroduced the Sunshine Protection Act, which would allow daylight time to be made permanent.

I have written before about the health risks of interfering with our circadian rhythms. There is an increasing body of evidence to suggest that the sudden loss of an hour’s sleep is bad for our health. During the first days after the change, many people suffer from symptoms such as irritability, less sleep, daytime fatigue and reduced immune function. More worryingly, heart attacks, strokes and workplace injuries can happen during the first weeks after a clock change compared with other weeks. There’s also an increase in fatal car crashes in the week we “spring forward”.

With the health evidence favouring a move to permanent standard time – with no clock change in the autumn – many doctors and scientists oppose legislation that would make daylight saving time permanent.


Moving away from the ongoing argument of the health benefits (a move to permanent standard time) versus the economic benefits (a move to daylight saving time) of time change, there is growing interest in chronotherapy – the treatment of an illness that incorporates the body’s natural rhythms and cycles. The 2017 Nobel Prize in Physiology or Medicine was awarded to Jeffrey C Hall, Michael Rosbash and Michael W Young for their work on discovering the molecular mechanisms controlling circadian rhythm. It has boosted research and interest in chronotherapy and in particular a link between circadian rhythms and the treatment of cancer.

Households could save €400 on energy if clocks do not go back, Dáil toldOpens in new window ]

The circadian rhythm is an internal clock that makes the brain cycle between intervals of alertness and sleepiness. Circadian rhythms comprise various elements that influence these intervals, including eating habits, body temperature and duration of sleep, as well as external factors such as darkness and lightness.

Chronotherapy in oncology treatment involves syncing the time at which cancer drugs are administered with a patient’s natural circadian rhythm with the aim of minimising side effects while maximising the effectiveness of the drug. This involves administering drugs when healthy cells are least prone to the toxicity of these drugs or when cancer cells are most vulnerable to the effects of the drug.

Researching chronotherapy is complex, not least because of the individual variations in our circadian rhythms. Its effectiveness is linked to your chronotype – basically whether you are a morning or a night-time person. This correlates with our internal molecular activity.

Therefore chronotherapy must be personalised to each specific patient even if a certain drug administration time is better for most patients on average.

How moving the clock forward this weekend could kill youOpens in new window ]

Not only do humans have optimal times for drug administration, but the drugs themselves have specific times in which they will be most effective. Because each class of chemotherapy has an individualised method of killing cells, each drug also has a window of time in which it is most productive. For example, fluorouracil, a chemotherapy drug given to treat a number of cancers, was noted to work best at night, while oxaliplatin, a drug used to treat advanced colorectal cancer, worked best when given during the afternoon.

The possible benefits of chronotherapy are not restricted to cancer. Researchers at the University of California found significant benefits for patients with bipolar disorder who took antidepressants at three specific intervals in their circadian rhythms to achieve sustained responses to the drugs.

Probably the last thing a patient taking chronotherapy needs is a regular change to our clocks. Moving to permanent daylight saving time or permanent standard time may be less important to our health than ceasing to tamper with time.