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New study shows major connection between exercise, sleep, and limited screen time with lower obesity risk in children

New findings suggest that meeting the Canadian 24-hour Movement Guidelines for physical activity, sleep, and screen time lead to significantly lower BMI and body fat in children. The guidelines recommend a minimum of 60 minutes of moderate-to-vigorous physical activity (MVPA) at least 5 days per week, sleeping 9-11 hours a night for children 5-13 or 8-10 hours a night for teens 14-18, and 2 hours or less of TV viewing per day. They found that children had a significantly lower likelihood of obesity for each guideline that they met.

Three-hundred and fifty-seven children from 5-18 participated in the study, about half African American and half white, all from Baton Rouge, LA. Over an 18 month period the researchers collected data from surveys, obtained BMI from height and weight measurements, and measured both visceral fat (stored in the abdominal area) and subcutaneous fat (stored under the skin) with MRI. The researchers found that only about one-third of the participants met the guidelines for MVPA and TV time, while just over half met the guidelines for sleep. More boys tended to meet physical activity guidelines while both boys and girls were equally as likely to meet TV and sleep guidelines.

Of the entire sample, 27% of children didn’t meet any of the guidelines and only 8% met all three. A significantly lower proportion of African American children met the guidelines compared to their white counterparts.

These findings are very important, as the same data found that the more guidelines that a child met, the less likely that child was to have a BMI in the overweight or obese range. In fact, children who met all three guidelines – which ideally should be every child! – had an impressive 89% lower likelihood of obesity than children who met none of the guidelines. Even for children meeting only one guideline or two guidelines, the odds were still significantly lower – 24% and 40% respectively. The study, conducted by Drs. Peter Katzmarzyk and Amanda Staiano at LSU’s Pennington Biomedical Research Center in Baton Rouge, LA, was presented at the recent European Congress on Obesity in Portugal.

These findings suggest that interventions targeting childhood obesity can have the biggest impact if they address multiple lifestyle factors, rather than just diet or exercise alone. Most importantly, these results show that improvements in any one of the three major guideline areas (physical activity, screen time, and sleep) can significantly decrease the odds of childhood obesity. Dr. Bernard Zinman, Professor at the University of Toronto, agreed that the study "confirms the robustness of the Canadian 24-Hour Movement Guidelines for Children and Youth.” Dr. Zinman told us that he hopes to see future studies that, "Evaluate the feasibility of introducing these healthy behaviors prospectively in at risk communities.”

Though this study provided a remarkable amount of information we still had a few lingering questions. Luckily, The diaTribe Foundation had the opportunity to follow up with Dr. Katzmarzyk:

The diaTribe Foundation (TdF): Which of the three variables (sleep, physical activity, or screen time) is the most important determinant for adiposity?

Dr. Peter Katzmarzyk (PK): There was no clear winner with respect to the three behaviors. I think all are important, and it is clear that the greater the number of components achieved, the better the health of the child with respect to adiposity and obesity.

TdF: How much confidence do you have in the reporting mechanism? Which self-reported variable is most reliable – sleep, TV time, or exercise?

PK: All data were recorded on questionnaires completed by the children, with the help of their parent when required (especially for the younger children). The reporting of the measurements was probably comparable across the different variables given that they were all questionnaire-derived. In other words, we didn’t have a mix of subjective and objective measurements – it was all subjective assessment.

TdF: Was there any effort to measure “screens” rather than just TV?

PK: We focused solely on TV time in this analysis. The ability to track use of different types of screens is becoming more difficult as time goes on. We used to be focused mainly on TV, and then computer time became important to include, followed by video games, etc. Now with the widespread use of smart phones and tablets it seems that it will be important to capture these devices as well. The challenge will be in understanding the context of different screen time – for example, not all screen use these days would be considered a “sedentary” behavior given people may use screens during exercise, such as during “exergaming.”

TdF: Is there any way to analyze screen time more narrowly? Was screen time measured only in “fewer or more” than two hours, or were more specific measurements made?

PK: It is possible to measure screen time more narrowly using a continuous time scale; however, in this study we were interested in the effects of meeting the guidelines so we did not look at the effects across a wider range of screen or TV time.


Jacqueline Anders and Ben Pallant contributed to the writing of this piece


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