London School of Hygiene & Tropical Medicine

Long, dark nights are with us now that the clocks have gone back, but they may be held at bay in future years after new research led by the London School of Hygiene & Tropical Medicine suggests that moving the clock forward all year round could be good for health.

The study - published in the Journal of Physical Activity and Health - found that children were the most physically active on long summer days, with the biggest effect showing between 5pm and 8pm on longer days. Importantly, daylight rather than the weather holds the key, according to the authors, because the effect was strongest in the late afternoon and early evenings, and because it remained constant even when bad weather was taken into account.

A team led by Dr Anna Goodman, NIHR funded Research Fellow at LSHTM, analysed information on the amount of physical activity done by children between the age of eight and 11 across the day, and examined how this pattern differed by day length.

To do this, instruments called accelerometers, which record body movements, were placed around the waists of 325 children in Hertfordshire in their daily routine for a total of 817 days spread over the four seasons.The highest overall level of activity (mainly outdoor play) was recorded during the long summer days (with 14 or more hours of daylight).

The researchers point out that the biggest difference between long days and short or medium days was between 5pm and 8pm which is what would be expected if day light rather than weather were the key factor.  In addition the trend remained constant after taking in account bad weather days (rain, cloudy sky and wind).

Dr Goodman says: “The fact that kids spend more time playing outdoors and are more physically active overall on these longer days could be important at a population-level for promoting their fitness and in preventing child obesity. This strengthens the public health argument for the Daylight Saving Bill currently under consideration by the House of Commons, which proposes putting the clocks forward by an extra hour all year round.”

Part of the explanation for the increased physical activity on longer days seemed to be the greater amount of time children spent playing.  On long days, the children recorded spending 22% of their time taking part in out-of-home play in afternoons and early evenings, while the figure decreased significantly when the day became shorter (13% on medium and short days; 12.6 to 10 hours and less than 9.5 hours respectively). Other activities like organised sports such as football were barely affected by the length of the day.

The research doesn’t examine why children spend less time playing outside on short, dark days, but the authors speculate that it may be a combination of children being less keen to play and their parents being less keen to let them.

The authors of the research conclude: “This represents the most direct evidence yet that (at least at some points of the year) redistributing daylight hours to the afternoon might prove an effective population-level intervention to promote child physical activity. In combination with the evidence that such measures would avert road traffic crashes and reduce greenhouse emissions, this study therefore bolsters the public health arguments in favour of daylight saving measures such as those currently under consideration in the UK.”