Exercising between 7 a.m. and 9 a.m. has been associated with having a lower waist circumference and body mass index than people who work out during midday or evening, according to a study published Tuesday in the journal Obesity.
The authors studied health and activity data from 5,285 people who had participated in the 2003 to 2006 cycles of the U.S. Center for Disease Control and Prevention's National Health and Nutrition Examination Survey. The researchers chose those specific years because that was when accelerometers, or activity trackers, were first used in the survey.
These findings held true regardless of sex, ethnicity, education, tobacco use, alcohol consumption or sedentary behavior. Additionally, even among people who all met the physical activity guidelines — at least 150 minutes per week — achieving this goal in the morning was associated with the lowest BMI and waist size.
Ma is planning on doing more studies to confirm the findings and whether there is a causal relationship between exercising in the morning and having a smaller BMI and waist size, he said.The reasons behind the findings may have to do with both physiology and lifestyle habits, experts said. In the latest study, morning exercisers were the most sedentary even though they had the lowest BMI and waist circumference.