Tongyu Ma, PhD, research assistant professor with the Health Sciences Department, Franklin Pierce University, Rindge, N.H., and colleagues studied data on almost 5,300 individuals, finding a strong association between moderate to vigorous physical activity (MVPA) and obesity.
The research, published in Obesity, showed that people who exercised in the morning had a lower body mass index than that of those who exercised at other times, even though they were more sedentary.
For the second study, Chirag J. Patel, PhD, associate professor of biomedical informatics at Harvard Medical School, Boston, and colleagues examined more than 93,000 individuals and found that morning and afternoon, but not evening, exercise reduced the risk for type 2 diabetes.
However, the results, published in Diabetologia, also indicated that people who undertook at least MVPA were protected against developing type 2 diabetes no matter what time of day they exercised.
Along with considering the timing of exercise, the authors suggest that it is “helpful to include some higher intensity activity to help reduce the risk of developing diabetes and other cardiovascular disease.”
Morning exercisers perform less physical activity
Dr. Ma and colleagues noted that “although a beneficial association among the levels of physical activity with obesity has been frequently reported, the optimal timing of physical activity for decreasing obesity remains controversial.”
The researchers analyzed data from the National Health and Nutrition Examination Survey for the 2003-2004 and 2005-2006 cycles, because accelerometry was implemented in those periods.
They included 5,285 individuals aged ≥ 20 years who had physical activity measured via an accelerometer worn on the right hip during waking hours for 7 consecutive days.
The diurnal pattern of MVPA was classified into three clusters by the established technique of K-means clustering analysis: morning (n = 642), midday (n = 2,456), and evening (n = 2,187).
The association between MVPA, diurnal pattern, and obesity was then assessed in linear regression models taking into account a range of potential confounding factors.
Overall, participants in the morning cluster were older and more likely to be female than those in the other clusters (P < .001 for both). They were also more likely to be nonsmokers (P = .007) and to have less than high school education (P = .0041).
Morning cluster individuals performed less physical activity and were more sedentary than those in the midday and evening groups (P < .001 for both), although they were more likely to be healthy eaters (P = .004), with a lower calorie intake (P < .001).
Individuals in the morning cluster had, on average, a lower body mass index than those in other clusters, at 27.4 vs. 28.4 in the midday cluster and 28.2 in the evening cluster (P for interaction = .02).
Morning cluster participants also had a lower waist circumference than participants in the midday or evening cluster: 95.9 cm, 97.9 cm, and 97.3 cm, respectively (P for interaction = .06).
The team reported that there was a strong linear association between MVPA and obesity in the morning cluster, whereas there was a weaker curvilinear association in the midday and evening clusters.
“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,” Rebecca Krukowski, PhD, professor, public health sciences, University of Virginia, Charlottesville, said in a release.
However, she noted that the cross-sectional nature of the study means that it is “not known whether people who exercise consistently in the morning may be systematically different from those who exercise at other times, in ways that were not measured in this study.
“For example, people who exercise regularly in the morning could have more predictable schedules, such as being less likely to be shift workers or less likely to have caregiving responsibilities that impede morning exercise,” said Dr. Krukowski, who was not involved in the study.