Exercising early each day may be the key to keeping weight under control, a study suggests.
Researchers found a strong association between weight and workout time, with a lower body mass index and smaller waists among those who exercised between 7am and 9am.
The connection was weaker in those in the middle of the day and evening groups.
To investigate the possible link, researchers tracked the movement of those who met the guidelines of 150 minutes of moderate-to-vigorous physical activity per week, splitting them into three groups depending on when they exercised during the day.
Moderate to vigorous activity was measured as 1,952 or more counts per minute on an accelerometer, which tracks movement in a similar way to a pedometer.
In addition to being leaner, people in the morning group also reported having healthier diets and consuming fewer calories per unit of body weight compared with people who exercised later in the day.
But they also spent significantly more time sitting or lying down than the others.
The researchers found that despite this, the lower body mass index and waist size in the morning group persisted.
Clinical psychologist Rebecca Krukowski, professor and co-director of the Community-Based Health Equity centre at the University of Virginia school of medicine, who was not involved in the study, said: “This is exciting new research that is consistent with a common tip for meeting exercise goals – that is, schedule exercise in the morning before emails, phone calls or meetings that might distract you.”
Researchers used data from the 2003-2004 and 2005-2006 cycles of the National Health and Nutrition Examination Survey by the Centres for Disease Control and Prevention in the US.
A total of 5,285 people were included and split into morning, middle of the day and evening exercisers.
Those in the morning group (642 people) were 10 to 13 years older than the two other groups.
It also had the highest percentage of women, and the majority of them were primarily non-Hispanic white, had a college or higher education and had never used tobacco or alcohol.
The researcher who led the study said the findings suggest when you exercise might be important.
“Our findings propose that the diurnal pattern of moderate to vigorous physical activity could be another important dimension to describe the complexity of human movement,” Tongyu Ma, assistant professor in the health sciences department at Franklin Pierce University, and in the department of rehabilitation sciences at the Hong Kong Polytechnic University.
The findings were published in Obesity, the Obesity Society's journal.
