New research shows even the fittest of young adults can’t escape the dangers of desk jobs and couch potato life
BOULDER, Colo. — Think your youth makes you bulletproof to aging? Your office chair might disagree. A new study suggests that millennials’ sedentary lifestyles are quietly accelerating their biological clocks, even as they fill their Instagram feeds with weekend warrior workout posts.
The research reveals that millennials now spend more than 60 hours per week sitting – between long commutes, computer-based workdays, and evenings spent streaming content or scrolling through social media. Researchers warn that extended sedentary behavior could be increasing their risk of heart disease and other age-related health conditions far earlier than previously thought.
This concerning finding emerges from research conducted by scientists at the University of Colorado Boulder and the University of California Riverside and published in the journal PLOS ONE.
The study examined over 1,000 former or current Colorado residents, including 730 twins, making it one of the first comprehensive investigations into how prolonged sitting affects key health measures in young adults. The findings challenge a common assumption among young adults that they don’t need to worry about the health impacts of their lifestyle choices until middle age.
“Young adults tend to think they are impervious to the impacts of aging. They figure, ‘My metabolism is great, I don’t have to worry until I’m in my 50s or 60s.’ But what you do during this critical time of life matters,” says lead researcher Ryan Bruellman in a statement.
The research focused on participants between the ages of 28 and 49, with an average age of 33. On average, these individuals reported sitting almost nine hours daily, with some participants sitting up to 16 hours. They averaged between 80 and 160 minutes of moderate physical activity weekly and less than 135 minutes of vigorous exercise – numbers that researchers believe are actually better than national averages due to Colorado’s active lifestyle.
The study measured two key indicators of cardiovascular and metabolic health: Body Mass Index (BMI) and the ratio of total cholesterol to high-density lipoprotein cholesterol (TC/HDL), also known as the Cardiac Risk Ratio. These measurements provide important insights into heart health and metabolic function, with higher numbers generally indicating increased health risks.
The findings were striking: those who sat for longer periods showed higher TC/HDL ratios and BMIs, even when meeting the minimum recommended physical activity guidelines of about 20 minutes per day of moderate exercise. Simply put, the more someone sat, the “older” their body appeared in terms of these health markers.
However, the research did identify one potential buffer against the effects of prolonged sitting: vigorous exercise. Participants who engaged in 30 minutes of vigorous daily activity – such as running or intense cycling – showed health markers similar to those of people five to 10 years younger who sat the same amount but didn’t exercise vigorously. Yet even this level of intense activity couldn’t completely neutralize the negative impacts of extended sitting.
The study’s use of twin participants proved particularly valuable in understanding these relationships. Because identical twins share 100% of their genes, comparing twins with different activity levels allowed researchers to isolate the specific effects of lifestyle choices on health outcomes. When examining twins with different sitting and exercise habits, the researchers discovered that replacing sitting time with exercise appeared more beneficial for cholesterol levels than simply adding exercise to a day full of sitting.
“Our research suggests that sitting less throughout the day, getting more vigorous exercise, or a combination of both may be necessary to reduce the risk of premature aging in early adulthood,” says senior author Chandra Reynolds, a professor in the Department of Psychology and Neuroscience and the Institute for Behavioral Genetics.
What exactly counts as “vigorous” exercise? Activities that really get your heart pumping – think running, fast cycling, high-intensity interval training, or vigorous swimming. These activities typically require more effort than moderate exercises like brisk walking or casual cycling.
The findings serve as a crucial wake-up call for young adults and suggest that current physical activity guidelines may need revision to account for our increasingly sedentary lifestyles. As Reynolds advises, “This is the time to build habits that will benefit health over the long term.”
Paper Summary
Methodology
The researchers collected data from participants in the Colorado Adoption/Twin Study of Lifespan Behavioral Development and Cognitive Aging (CATSLife). Participants self-reported their sitting time, including work, travel, television watching, and computer use. They also reported their physical activities, which were assigned metabolic equivalent of task (MET) scores based on intensity. Activities with MET scores between 3-6 were classified as moderate, while those above 6 were considered vigorous.
The study measured participants’ height and weight and collected blood samples to analyze cholesterol levels. By including twins in the study, researchers could control for genetic and environmental factors that might influence health outcomes.
Key Results
The study found significant relationships between sitting time, exercise intensity, and health markers. On average, participants reported sitting about 8.58 hours per day. Both excessive sitting and insufficient vigorous exercise were associated with worse health outcomes.
The research showed that 30 minutes of daily vigorous exercise could provide health benefits equivalent to being 5-10 years younger in terms of certain health markers. However, for people sitting more than 8 hours per day, current exercise guidelines weren’t enough to maintain optimal health markers, particularly for cardiovascular risk factors.
Study Limitations
The research relied on self-reported data for sitting time and physical activity, which might not be as accurate as objective measurements. The sample was predominantly non-Hispanic European American (90.1%), limiting the generalizability to other populations. The study couldn’t make inferences about individuals who may have been medically advised against vigorous exercise or those using mobility aids. Additionally, while the study measured fruit and vegetable consumption, it didn’t capture comprehensive dietary information that might influence health outcomes.
Discussion & Takeaways
The study provides strong evidence that both reducing sitting time and increasing vigorous exercise are important for maintaining cardiovascular and metabolic health in early adulthood. The findings suggest that current physical activity guidelines might need to be adjusted to account for daily sitting time. The research particularly emphasizes the importance of vigorous exercise over moderate activity in counteracting the effects of prolonged sitting. The twin analysis provided unique insights into how lifestyle choices can influence health outcomes even among individuals with identical genetic backgrounds.
Funding & Disclosures
The research was supported by the U.S. National Institutes of Health (NIH), National Institute on Aging grant AG046938. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The authors declared no competing interests. The study was approved by the Institutional Review Boards at the Institute for Behavioral Genetics – University of Colorado, Boulder, and the University of California, Riverside.
