The week after the autumn clock change is associated with a reduction in demand for NHS services for sleep disorders, cardiovascular disease, anxiety, depression, and psychiatric conditions in England, finds a study in the Christmas issue of The BMJ.
However, there is little evidence that the spring clock change has any short term effect on the number of health conditions, say the researchers.
Daylight saving time was introduced during the first world war and involves moving the clocks one hour forward in spring and one hour back in autumn. It operates in around 70 countries and affects a quarter of the world's population.
Yet some studies (mainly outside the UK) have suggested that the clock changes, particularly the spring clock change, have a detrimental effect on health, leading to calls for them to be abolished.
To obtain a clearer picture, researchers set out to explore the short term (acute) effects of the clock changes on people's mental and physical health in England.
Their findings are based on linked primary and secondary care records for 683,809 people with at least one of eight health events in the weeks surrounding the spring or autumn clock changes from 2008 to 2019.
The health events analysed were anxiety, major acute cardiovascular disease, depression, eating disorder, road traffic injury, self-harm, or sleep disorder in primary or secondary care or a psychiatric condition in accident and emergency.
The mean daily number of events (per year, per region) in the first week after the clock changes were compared with those in the control period (four weeks before the changes and weeks 2-4 after).
In the week after the autumn clock change, five health conditions had fewer events: anxiety (a 3% reduction from 17.3 events per day to 16.7), acute cardiovascular disease (a 2% reduction from 50 events per day to 48.9), depression (a 4% reduction from 44.6 to 42.7), psychiatric conditions (a 6% reduction from 3.5 to 3.3), and sleep disorders (an 8% reduction from 5.4 to 4.9).
Little evidence was found of reductions in eating disorder diagnoses, road traffic injuries, or self-harm or of changes after the spring clock change.
This is an observational study, so no firm conclusions can be drawn about cause and effect, and the authors note that health records contain only events for which the individual seeks medical help, and the date that a health event is recorded by a clinician, which is not necessarily the date of symptom onset.
However, they say the results are based on 12 years of broadly representative general practice and hospital data, giving a more complete picture of the effect of the clock changes on demand for health services than previous studies.
They suggest that the extra sleep over the Autumn clock change and the abrupt increase in morning sunlight exposure after the transition may be beneficial to health.
And they conclude: "Our study contributes to the ongoing debate about England's clock change policy. Future research should explore the mechanisms underlying the reduction in health events that we observed after the autumn clock change."
