Morning exercise linked to lower BMI, waist circumference for adults
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Key takeaways:
- Adults who perform physical activity in the morning have a lower BMI than those who exercise at midday or in the evening.
- More randomized controlled trials are needed to confirm the findings.
Adults who exercise in the morning have a lower BMI and waist circumference than those who exercise in the afternoon or evening, according to study findings published in Obesity.
“Physical activity at any time of the day is beneficial, but there may be an optimal time of day to augment the benefits,” Tongyu Ma, PhD, a research assistant professor of sports science and musculoskeletal health at Hong Kong Polytechnic University, told Healio. “To date, time-of-day influences are still poorly understood.”
Ma and colleagues obtained accelerometry data from 5,285 adults aged 20 years and older who participated in the 2003-2004 and 2005-2006 National Health and Nutrition Examination Survey cycles. Participants wore an accelerometer on their right hip for 7 consecutive days following an on-site examination. Accelerometer data were used to classify physical activity as sedentary behavior, light-intensity physical activity or moderate to vigorous physical activity. Proportions of total moderate to vigorous physical activity accumulated in each hour were used to cluster adults into three groups: morning physical activity (n = 642), midday physical activity (n = 2,456) and evening physical activity (n = 2,187). BMI and waist circumference were collected during an on-site examination.
Among adults who met physical activity guidelines of 150 minutes of moderate to vigorous physical activity per week, there were no differences in the volume of moderate to vigorous physical activity between the time-of-day groups. For those who did not meet guidelines, the volume of moderate to vigorous physical activity was about 40% higher in the midday and evening compared with the morning.
Adults who performed moderate to vigorous physical activity in the morning had a mean BMI of 27.4 kg/m2 compared with a BMI of 28.4 kg/m2 in the midday physical activity group and a BMI of 28.2 kg/m2 with evening physical activity. The morning physical activity group had a mean waist circumference of 95.9 cm compared with a 97.9 cm waist circumference for those performing moderate to vigorous physical activity during midday and a 97.3 cm waist circumference for adults in the evening physical activity group.
“[The findings were] not surprising because the existing evidence suggests that morning physical activity might be more beneficial for weight management,” Ma said.
The results were unchanged after adjustments for dietary factors and total activity count. In a sensitivity analysis of a subsample of adults without chronic disease at baseline, the effect of moderate to vigorous physical activity timing on BMI and waist circumference was attenuated.
Ma said more randomized controlled trials are needed to confirm the study’s findings.
For more information:
Tongyu Ma, PhD, can be reached at mat@franklinpierce.edu.
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