‘Goldilocks Day’ calls for more sleep, physical activity for optimal child bone health
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Days filled with more sleep and vigorous physical activity and less sedentary time were associated with good overall skeletal health in children, according to data published in the Journal of Bone and Mineral Research.
“Children’s activities throughout the whole 24-hour day appear to be important for their bone health — getting as much physical activity (the more vigorous the better) and as little sedentary time as possible while also meeting sleep guidelines for their age,” Dorothea Dumuid, PhD, a National Health and Medical Research Council early career research fellow at the University of South Australia, told Healio.
Researchers analyzed data from the Child Health CheckPoint study conducted within the Longitudinal Study of Australian Children between February 2015 and March 2016 (n = 804; aged 10.7 to 12.9 years; 50% boys). Participants visited a CheckPoint assessment center, where they were fitted with an accelerometer on their nondominant wrist. The accelerometer was to be worn for 8 days, 24 hours a day. Children were asked to complete a log, recording bed and wake times, as well as time and reason for accelerometer removal.
Peripheral quantitative CT scans were used to measure skeletal health on the nondominant leg at the ankle and shin sites. Skeletal health measures included volumetric bone mineral density and bone geometric parameters. Predicted bone outcomes were calculated based on the recorded physical activity, sedentary and sleep times of the participants. Ideal times for each activity were calculated using the top 5% of each bone measurement to calculate what researchers called the “Goldilocks Day.”
Sleep, activity balance
“We already knew that high levels of physical activity were beneficial for children’s bone health, but it is not possible for children to get more physical activity in a day without giving up time in other activities such as sleep or sitting,” Dumuid said. “We know very little about the relationships between children’s sleep duration and sitting time and their skeletal health, let alone how daily time should best be balanced across these activities. The Goldilocks Day tells us the best daily balance of these activities, where the durations of physical activity, sleep and sitting are ‘just right’ for optimal bone health.”
Sleep and moderate to vigorous physical activity were positively associated with all bone measures except for cortical density, whereas sedentary time was negatively associated. Both boys and girls saw benefits with more moderate to vigorous physical activity, whereas added sleep was more beneficial to boys than girls.
Girls who were less advanced in puberty had better skeletal health with more moderate to vigorous activity and less low physical activity, and longer sleep duration was associated with better bone circumference, polar moment of inertia and polar stress-strain index. Girls more advanced in puberty had the opposite association for physical activity and had better skeletal health with less sleep and sedentary time.
‘Just right’ amounts
Researchers said the average amount of time 11- and 12-year-olds should spend on each activity for ideal bone health is 10.9 hours of sleep, 8.2 hours of sedentary time, 3.4 hours of low physical activity and 1.5 hours of moderate to vigorous physical activity. When stratified by sex, the ideal day for boys included 2.4 more hours of sleep, 1.7 fewer hours of sedentary time, 0.6 fewer hours of low physical activity and 0.1 fewer hours of moderate to vigorous physical activity than girls.
“Parents, caregivers and clinicians want to know how much time their children should spend sleeping, in sedentary behaviors and in different intensities of physical activity,” Dumuid said. “Until now, the research evidence has not directly addressed this question. It has looked at the relationships between individual activities and bone strength rather than identifying optimal durations across a day. Our study provides some of the first supporting evidence for children’s daily activity guidelines and provides daily activity targets that families can work toward.”
Dumuid said future research should follow children over time and assess specific schedules to examine their impact on skeletal health. She added that studies should also be done on other populations.
“It will be important to consider other kinds of health outcomes when formulating activity guidelines for children,” Dumuid said. “The current study explores the Goldilocks Day for bone health only, but some compromises may be required to achieve a Goldilocks Day for overall health and well-being, incorporating other outcomes such as adiposity, cognition and quality of life.”
For more information:
Dorothea Dumuid, PhD, can be reached at dot.dumuid@unisa.edu.au.
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