Researchers found a curious mitochondrial pattern in people who moved more

Researchers tracked daily movement alongside a blood-based mitochondrial marker, revealing an intriguing pattern across different levels of physical activity.

Study: Association between habitual physical activity and mitochondrial DNA copy number in healthy middle-aged adults. Image Credit: beeboys

In a recent study published in the journal Scientific Reports, a group of researchers examined whether everyday physical activity was associated with leukocyte mitochondrial deoxyribonucleic acid copy number (mtDNAcn), a blood-based marker related to mitochondrial content and functional capacity, in middle-aged adults.

Background

Is everyday movement linked to markers of mitochondrial health? Physical inactivity and sedentary behavior are associated with metabolic disorders, including obesity, type 2 diabetes, and cardiovascular disease.

Mitochondrial dysfunction is linked to oxidative stress, reactive oxygen species (ROS), and metabolic disruption. Mitochondrial DNA copy number provides an indirect measure of mitochondrial content and functional capacity. Lower mtDNAcn has been associated with aging, coronary heart disease, and diabetic nephropathy.

Physical activity can influence mitochondrial biogenesis and oxidative capacity, but researchers know less about how ordinary daily movement relates to mtDNAcn in healthy middle-aged adults. Evidence is particularly limited on whether light, moderate, and vigorous activity show different relationships with this marker and whether findings differ between self-reported and device-measured activity.

About the study

The cross-sectional study included 256 adults aged 45-64 years in the Republic of Korea. The participants were community-dwelling and generally healthy. Written informed consent was obtained, and Institutional Review Board (IRB) approval was granted by Keimyung University.

Venous blood was collected after a 12-hour fast. Researchers extracted DNA from the blood samples and measured mtDNAcn using a quantitative polymerase chain reaction laboratory assay.

Participants also completed a questionnaire covering walking, moderate and vigorous activity, and time spent sitting during the previous week. This allowed the researchers to estimate overall activity and classify participants according to their usual activity level.

Objective measures of activity were obtained using a waist-worn accelerometer over three consecutive weekdays. The device recorded participants’ usual movement throughout the day and categorized activity into sedentary time and light, moderate, and vigorous activity.

The researchers then examined whether the different activity measures were associated with mtDNAcn. The analyses accounted for sex, age, education, shift work, alcohol consumption, smoking, comorbidity, and sleep quality.

Study results

The 256 participants had a mean age of about 54 years, and 60.2% were female. Valid accelerometer measurements were available for 205 participants. Participants with and without valid accelerometer data did not differ significantly in mtDNAcn or in most measured characteristics, although sex distribution differed.

Self-reported activity indicated that walking accounted for the largest share of participants’ weekly physical activity. Based on the questionnaire, about 42% were classified as moderately active, 33% as having low activity, and 25% as highly active.

Accelerometer measurements showed that participants spent about 5 hours per day in light activity and about 37 minutes in moderate activity. Vigorous activity was uncommon, averaging just over one minute per day. Participants also spent a large part of their monitored day sedentary.

People who reported more total physical activity and more walking tended to have higher mtDNAcn. The same pattern appeared for light activity measured by the accelerometer. Sedentary time and objectively measured moderate- and vigorous-intensity activity were not significantly associated with mtDNAcn.

After adjustment for demographic, lifestyle, and health factors, the associations with self-reported total activity, walking, and device-measured light activity remained. The regression models explained only a small proportion of the variation in mtDNAcn, indicating that physical activity represents only one of several possible influences on this mitochondrial marker.

The findings therefore linked greater overall activity, walking, and light daily movement with higher mtDNAcn, but they did not show a similar relationship for moderate or vigorous activity. The small amount and limited variability of higher-intensity activity, especially vigorous activity, may have reduced the study’s ability to detect such associations.

Conclusions

The study found that light activity measured by an accelerometer, along with self-reported overall activity and walking, was associated with higher mitochondrial DNA copy number in healthy middle-aged community-dwelling adults. These associations remained after adjustment for demographic and lifestyle factors.

The results suggest that ordinary daily movement, including walking and other light activity, may be relevant to mitochondrial health in middle age. However, the study does not show that light activity is better for mitochondria than moderate or vigorous exercise.

Because physical activity and mtDNAcn were measured at the same time point, the researchers cannot determine which came first. Greater daily movement may be associated with higher mtDNAcn, but people with better underlying mitochondrial health may also be more likely to remain physically active.

The accelerometer covered only three weekdays and did not capture weekend activity, while the low volume of higher-intensity activity limited interpretation of the null findings at those intensities. The biological processes that might connect light activity with mtDNAcn were also not measured directly.

Longitudinal and interventional studies are still needed to determine whether light daily activity helps maintain mitochondrial DNA copy number over time or whether the association reflects other aspects of health and fitness.