The new study suggests more daylight in the evenings is linked to increased physical activity, providing evidence for proposals to push the clocks forward by an additional hour year round.
The researchers, from the London School of Hygiene and Tropical Medicine and the University of Bristol in the UK, report their findings in the International Journal of Behavioral Nutrition and Physical Activity.
In various parts of the world, there have been proposals to permanently shift the clocks forward an additional hour. For example, in 2010-12, the British Parliament discussed proposals to do this, which would have meant British children would experience around 200 extra waking daylight hours per year.
However, there was no evidence cited at the time to support claims that more waking daylight hours would be associated with more physical activity.
As such, the researchers, led by Anna Goodman of the London School of Hygiene and Tropical Medicine, studied more than 23,000 children between the ages of 5-16 years from nine countries. Each child wore accelerometers to measure their body movement, and the researchers used their average physical activity level as their primary outcome.
Additionally, the team matched the data to time of sunset and weather characteristics, including daily precipitation, humidity, wind speed and temperature.
'Additional daylight saving measures could yield worthwhile public health benefits'
After looking at the children's activity levels in relation to the time of sunset, the team found that total daily activity levels were 15-20% higher on summer days - when the sun went down after 9 pm - compared with winter days - when the sun set before 5 pm.
The researchers say their study suggests that extra daylight saving measures would result in an average of 2 extra minutes of physical activity for each child each day.
Though 2 minutes may not sound like a lot of time, the team says that children amass an average of 33 minutes a day of moderate-to-vigorous physical activity per day; as such, an extra 2 minutes represents a 5% increase, which could be a "step in the right direction."
Furthermore, these increased physical activity effects applied to girls and boys; overweight, obese and normal weight children; and children across all socioeconomic backgrounds.
Commenting on their findings, Goodman says:
"This study provides the strongest evidence to date that, in Europe and Australia, evening daylight plays a role in increasing physical activity in the late afternoon and early evening - the 'critical hours' for children's outdoor play.Introducing additional daylight savings measures would affect each and every child in the country, every day of the year, giving it a far greater reach than most other potential policy initiatives to improve public health."
Though they had a large sample size, the researchers do note some limitations to their study. Firstly, their data were cross-sectional, not longitudinal - though they could follow the same child across the week the clocks were changed, they could not follow the children across an entire year.
Additionally, they say their estimates are subject to some residual confounding by weather, which could account for why slight activity level differences were observed as early as 2 pm on weekends and holidays.
Finally, most of their study populations came from high-income European settings, so the team admits more research is needed to establish generalizability across other populations.
Still, the researchers conclude their study by noting that "shifting the physical activity mean of the entire population [and introducing] additional daylight saving measures could yield worthwhile public health benefits."
A recent study suggested setting clocks ahead 1 hour in the spring may accelerate cardiac events.