Limits...
Daylight saving time as a potential public health intervention: an observational study of evening daylight and objectively-measured physical activity among 23,000 children from 9 countries.

Goodman A, Page AS, Cooper AR, International Children’s Accelerometry Database (ICAD) Collaborato - Int J Behav Nutr Phys Act (2014)

Bottom Line: Adjusting for child and weather covariates, we found that longer evening daylight was independently associated with a small increase in daily physical activity.Moreover, these small effect sizes actually compare relatively favourably with the typical effect of intensive, individual-level interventions.We therefore conclude that, by shifting the physical activity mean of the entire population, the introduction of additional daylight saving measures could yield worthwhile public health benefits.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK. anna.goodman@LSHTM.ac.uk.

ABSTRACT

Background: It has been proposed that introducing daylight saving measures could increase children's physical activity, but there exists little research on this issue. This study therefore examined associations between time of sunset and activity levels, including using the bi-annual 'changing of the clocks' as a natural experiment.

Methods: 23,188 children aged 5-16 years from 15 studies in nine countries were brought together in the International Children's Accelerometry Database. 439 of these children were of particular interest for our analyses as they contributed data both immediately before and after the clocks changed. All children provided objectively-measured physical activity data from Actigraph accelerometers, and we used their average physical activity level (accelerometer counts per minute) as our primary outcome. Date of accelerometer data collection was matched to time of sunset, and to weather characteristics including daily precipitation, humidity, wind speed and temperature.

Results: Adjusting for child and weather covariates, we found that longer evening daylight was independently associated with a small increase in daily physical activity. Consistent with a causal interpretation, the magnitude of these associations was largest in the late afternoon and early evening and these associations were also evident when comparing the same child just before and just after the clocks changed. These associations were, however, only consistently observed in the five mainland European, four English and two Australian samples (adjusted, pooled effect sizes 0.03-0.07 standard deviations per hour of additional evening daylight). In some settings there was some evidence of larger associations between daylength and physical activity in boys. There was no evidence of interactions with weight status or maternal education, and inconsistent findings for interactions with age.

Conclusions: In Europe and Australia, evening daylight seems to play a causal role in increasing children's activity in a relatively equitable manner. Although the average increase in activity is small in absolute terms, these increases apply across all children in a population. Moreover, these small effect sizes actually compare relatively favourably with the typical effect of intensive, individual-level interventions. We therefore conclude that, by shifting the physical activity mean of the entire population, the introduction of additional daylight saving measures could yield worthwhile public health benefits.

Show MeSH

Related in: MedlinePlus

Mean physical activity across the hours of the day, comparing children either side of the changing of the clocks. CI = confidence interval, cpm = counts per minute. Analysis based on 1830 schooldays from 439 children from 11 studies in 9 countries. Analyses restricted to children with at least one valid schoolday measurement day both before and after the clocks changed; to increase power, data from across the spring and autumn clock changes are pooled. Hours are grouped into two-hour time periods to increase power and are rounded down, e.g. ‘7-8’ covers ‘07:00–08:59’. Adjustment was not essential as each child serves as his or her own control, but the results were similar in adjusted analyses.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC4364628&req=5

Fig3: Mean physical activity across the hours of the day, comparing children either side of the changing of the clocks. CI = confidence interval, cpm = counts per minute. Analysis based on 1830 schooldays from 439 children from 11 studies in 9 countries. Analyses restricted to children with at least one valid schoolday measurement day both before and after the clocks changed; to increase power, data from across the spring and autumn clock changes are pooled. Hours are grouped into two-hour time periods to increase power and are rounded down, e.g. ‘7-8’ covers ‘07:00–08:59’. Adjustment was not essential as each child serves as his or her own control, but the results were similar in adjusted analyses.

Mentions: Consistent with a causal interpretation, hour-by-hour analyses indicated that it was in the late afternoon and evening that the duration of evening daylight was most strongly associated with hourly physical activity levels (Figure 2). This was true on both schooldays and weekend/holiday days, with the period of the day when physical activity fell fastest corresponding to the timing of sunset (e.g. falling fastest between 18:00 and 19:00 on days when the sun also set between those hours). Similarly, when comparing the subsample of 439 children who were measured on schooldays immediately before and immediately after the changing of the clocks, there was strong evidence that children were more active during the evening of the days with later sunset (Figure 3). Between 17:00 and 20:59 the mean increase in physical activity on the days with later sunset was 94 cpm per hour (95% CI 62, 125); the equivalent increase in percent of time spent in MVPA was 0.84% (95% CI 0.40%, 1.28%) or 2.0 minutes.Figure 2


Daylight saving time as a potential public health intervention: an observational study of evening daylight and objectively-measured physical activity among 23,000 children from 9 countries.

Goodman A, Page AS, Cooper AR, International Children’s Accelerometry Database (ICAD) Collaborato - Int J Behav Nutr Phys Act (2014)

Mean physical activity across the hours of the day, comparing children either side of the changing of the clocks. CI = confidence interval, cpm = counts per minute. Analysis based on 1830 schooldays from 439 children from 11 studies in 9 countries. Analyses restricted to children with at least one valid schoolday measurement day both before and after the clocks changed; to increase power, data from across the spring and autumn clock changes are pooled. Hours are grouped into two-hour time periods to increase power and are rounded down, e.g. ‘7-8’ covers ‘07:00–08:59’. Adjustment was not essential as each child serves as his or her own control, but the results were similar in adjusted analyses.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4364628&req=5

Fig3: Mean physical activity across the hours of the day, comparing children either side of the changing of the clocks. CI = confidence interval, cpm = counts per minute. Analysis based on 1830 schooldays from 439 children from 11 studies in 9 countries. Analyses restricted to children with at least one valid schoolday measurement day both before and after the clocks changed; to increase power, data from across the spring and autumn clock changes are pooled. Hours are grouped into two-hour time periods to increase power and are rounded down, e.g. ‘7-8’ covers ‘07:00–08:59’. Adjustment was not essential as each child serves as his or her own control, but the results were similar in adjusted analyses.
Mentions: Consistent with a causal interpretation, hour-by-hour analyses indicated that it was in the late afternoon and evening that the duration of evening daylight was most strongly associated with hourly physical activity levels (Figure 2). This was true on both schooldays and weekend/holiday days, with the period of the day when physical activity fell fastest corresponding to the timing of sunset (e.g. falling fastest between 18:00 and 19:00 on days when the sun also set between those hours). Similarly, when comparing the subsample of 439 children who were measured on schooldays immediately before and immediately after the changing of the clocks, there was strong evidence that children were more active during the evening of the days with later sunset (Figure 3). Between 17:00 and 20:59 the mean increase in physical activity on the days with later sunset was 94 cpm per hour (95% CI 62, 125); the equivalent increase in percent of time spent in MVPA was 0.84% (95% CI 0.40%, 1.28%) or 2.0 minutes.Figure 2

Bottom Line: Adjusting for child and weather covariates, we found that longer evening daylight was independently associated with a small increase in daily physical activity.Moreover, these small effect sizes actually compare relatively favourably with the typical effect of intensive, individual-level interventions.We therefore conclude that, by shifting the physical activity mean of the entire population, the introduction of additional daylight saving measures could yield worthwhile public health benefits.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK. anna.goodman@LSHTM.ac.uk.

ABSTRACT

Background: It has been proposed that introducing daylight saving measures could increase children's physical activity, but there exists little research on this issue. This study therefore examined associations between time of sunset and activity levels, including using the bi-annual 'changing of the clocks' as a natural experiment.

Methods: 23,188 children aged 5-16 years from 15 studies in nine countries were brought together in the International Children's Accelerometry Database. 439 of these children were of particular interest for our analyses as they contributed data both immediately before and after the clocks changed. All children provided objectively-measured physical activity data from Actigraph accelerometers, and we used their average physical activity level (accelerometer counts per minute) as our primary outcome. Date of accelerometer data collection was matched to time of sunset, and to weather characteristics including daily precipitation, humidity, wind speed and temperature.

Results: Adjusting for child and weather covariates, we found that longer evening daylight was independently associated with a small increase in daily physical activity. Consistent with a causal interpretation, the magnitude of these associations was largest in the late afternoon and early evening and these associations were also evident when comparing the same child just before and just after the clocks changed. These associations were, however, only consistently observed in the five mainland European, four English and two Australian samples (adjusted, pooled effect sizes 0.03-0.07 standard deviations per hour of additional evening daylight). In some settings there was some evidence of larger associations between daylength and physical activity in boys. There was no evidence of interactions with weight status or maternal education, and inconsistent findings for interactions with age.

Conclusions: In Europe and Australia, evening daylight seems to play a causal role in increasing children's activity in a relatively equitable manner. Although the average increase in activity is small in absolute terms, these increases apply across all children in a population. Moreover, these small effect sizes actually compare relatively favourably with the typical effect of intensive, individual-level interventions. We therefore conclude that, by shifting the physical activity mean of the entire population, the introduction of additional daylight saving measures could yield worthwhile public health benefits.

Show MeSH
Related in: MedlinePlus