Can exercise undo sitting's health risks? New study suggests vigorous activity helps

Research finds 30 minutes of vigorous daily exercise may counter some aging effects of prolonged sitting, though reducing sitting time remains essential.

In a recent study published in PLoS ONE, a group of researchers investigated the interplay between physical activity intensity and sitting behavior in influencing health outcomes, specifically focusing on cardiovascular and metabolic biomarkers in adults aged 28-49.

Background 

Sitting for longer periods has become prevalent in developed nations, driven by changes in work environments and technology use. The coronavirus disease 2019 (COVID-19) pandemic intensified this trend, with many United States (U.S.) adults sitting over eight hours daily.

Sedentary lifestyles are linked to detrimental health outcomes, particularly in cardiovascular and metabolic domains, and may heighten mortality risks comparable to obesity and smoking. Additionally, prolonged sitting correlates with obesity and dyslipidemia, emphasizing the need to understand its relationship with aging.

Investigating these dynamics is essential for developing effective public health strategies that address the implications of sedentary behavior on health. Further research is necessary to clarify these complex interactions.

About the study 

Participants in this study were drawn from the Colorado Adoption/Twin Study of Lifespan Behavioral Development and Cognitive Aging (CATSLife), with recruitment occurring from July 2015 to March 2021. The sample included 1,327 individuals (53% female) with a mean age of 33.2 years (SD = 4.9).

Ethical approval was obtained from the Institutional Review Boards at the Institute for Behavioral Genetics–University of Colorado, Boulder, and the University of California, Riverside. Informed consent was acquired from all participants.

The CATSLife cohort comprises two groups: the Colorado Adoption Project, which includes adopted and non-adopted siblings, and the Longitudinal Twin Study, composed of same-sex monozygotic (MZ) and dizygotic (DZ) twin pairs.

To reduce confounding factors, certain exclusion criteria were applied, such as current pregnancy, non-fasting status during blood draws, and participants not completing the necessary measurements. This left 921 participants for the total cholesterol (TC)/high-density lipoprotein (HDL) analysis and 937 for the body mass index (BMI) analysis. Sedentary behavior was self-reported, while physical activity levels were assessed through leisure activity screening questionnaires.

Health biomarkers, including BMI, TC, and HDL, were measured through in-person visits and fasting blood draws. The analytical strategy involved using linear mixed-effects models to examine relationships between lifestyle factors and health outcomes while accounting for covariates such as sex, age, and dietary intake.

Co-twin control analyses were also performed to differentiate familial and environmental impacts on health metrics. Further sensitivity analyses on discordant MZ twin pairs provided insights into how physical activity might offset the health risks associated with prolonged sitting.

Study results 

Descriptive statistics for key measures revealed that participants, on average, reported sitting for 60.07 hours per week, equating to approximately 8.58 hours per day. The distribution of sitting hours was approximately normal, with no significant sex differences in average sitting time.

However, significant differences were observed between males and females in various measures, including the vigorous metabolic equivalent of tasks (METs), fruit and vegetable intake, BMI, and the TC/HDL ratio, with males exhibiting higher values (p ≤ .005). The correlation between BMI and TC/HDL was moderate, evidenced by Spearman’s rank correlation coefficient of 0.41.

Linear mixed-effect (LME) models were employed to analyze the sociodemographic effects on TC/HDL and BMI. Results indicated significant effects of age and sex on both outcomes, with age being positively associated with higher TC/HDL (B = 0.029, p < .001) and BMI (B = 0.087, p = .004).

While race and ethnicity did not yield significant results, they were retained in subsequent models. Non-linear trends were examined but found to be insignificant. The findings suggested that increased vigorous METs were linked to lower TC/HDL ratios, while older age, male sex, and longer sitting times correlated with worse TC/HDL outcomes.

Although healthy eating was associated with lower TC/HDL ratios, these effects were not statistically significant. Notably, a 30-year-old individual sitting an average of four hours daily would have a comparable TC/HDL to a 35-year-old engaging in 30 minutes of vigorous exercise daily.

Similar patterns emerged for BMI, indicating that those adhering to exercise recommendations could maintain a TC/HDL ratio that placed them in a moderate risk category for cardiovascular issues in early adulthood.

Co-twin control analysis indicated significant within-pair effects for sitting and vigorous physical activity concerning TC/HDL, suggesting a possible exposure effect rather than familial confounding. However, the MZ within-pair effect for vigorous activity was smaller, indicating partial confounding. Between-pair effects for vigorous exercise were noted but were not significant.

The discordant MZ twin analysis illustrated that twins who sat less and engaged in more vigorous activity exhibited lower TC/HDL ratios, particularly when vigorous activity replaced sitting time at a ratio of at least 10 minutes of exercise for each hour of sitting.

Conversely, the Active Compensator group required significantly more vigorous activity to achieve similar TC/HDL levels compared to their Active Replacer counterparts, highlighting the differential impact of physical activity on health outcomes within twin pairs.

Conclusions

To summarize, findings indicated that sitting negatively impacted health, and current exercise recommendations did not fully reduce these effects.

Engaging in vigorous activity was linked to healthier TC/HDL and BMI levels, with those sitting for 8.5 hours daily still at moderate cardiac risk.

The co-twin control analysis highlighted the importance of exceeding current exercise guidelines. Additionally, while fruit and vegetable intake was significant for BMI, it did not correlate with TC/HDL, indicating complex dietary influences.

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