Between long commutes, Zoom-packed workdays and evenings of streaming and scrolling, millennials now spend more than 60 hours per week sitting, potentially boosting their heart disease risk and accelerating other signs of aging, according to new CU Boulder and University of California Riverside research.

The study of more than 1,000 former or current Colorado residents, including 730 twins, is among the first to explore how prolonged sitting impacts health measures such as cholesterol and body mass index (BMI) in young adults.

It found that meeting the minimum recommended physical activity guidelines-;about 20 minutes per day of moderate exercise-;isn’t enough to counter the hazards of spending most waking hours in a seat.

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.” 

Chandra Reynolds, study’s senior author, professor in the Department of Psychology and Neuroscience and the Institute for Behavioral Genetics

For the study, published in the journal PLOS ONE, Reynolds teamed up with first author Ryan Bruellman, a doctoral candidate in the Department of Genetics, Genomics and Bioinformatics at UC Riverside.

After the COVID pandemic, Bruellman noticed that he and other people his age were sitting more. He set out to learn more about the consequences.

“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,'” said Bruellman. “But what you do during this critical time of life matters.”

A walk after work isn’t enough

The authors analyzed data from participants ranging in age from 28 to 49, average age 33, from CU’s Colorado Adoption/Twin Study of Lifespan behavioral development and cognitive aging (CATSLife), which has followed twins and adopted individuals since childhood.

On average, participants reported sitting almost 9 hours daily, with some sitting as much as 16 hours. They reported between 80 and 160 minutes of moderate physical activity on average weekly and less than 135 minutes of vigorous exercise weekly. The authors note that these results are likely better than national averages due to Colorado’s active lifestyle.

The researchers looked at two key measures of heart and metabolic aging: total cholesterol/high-density lipoprotein and body mass index (BMI). The study found that, essentially, the more one sat, the older one looked. And adding a little moderate activity on top of a long day of sitting did little to buffer these impacts.

In fact, young adults who sat 8.5 hours per day and performed at or below current exercise recommendations could enter a “moderate to high risk” category for cardiovascular and metabolic disease, the authors said.

“Taking a quick walk after work may not be enough,” said Reynolds. “While this is increasingly apparent with age, we show that associations are already emerging in early adulthood.”

Adding vigorous activity did have a buffering effect.

For instance, those who exercised vigorously (think running or cycling) for 30 minutes daily had cholesterol and BMI measures that looked like those of individuals five to 10 years younger who sat as much as they did but didn’t exercise.

But even vigorous activity could not fully buffer the negative impacts of prolonged sitting, the study concluded.

Same genes, different lifestyles

Identical twins are particularly useful to study because they share 100% of their genes, making it easier to rule out genetic factors that might contribute to different health outcomes and zero in on lifestyle differences.

When looking at a subset of twins with different sitting and physical activity habits, the researchers found that replacing sitting with exercise seemed to work better to improve cholesterol than simply adding exercise to a full day of sitting.

Bottom line, the researchers said: Try to do both.

Use a standing desk, take breaks and organize walking meetings to reduce sitting time at work. If possible, do something that gets you out of breath for at least 30 minutes per day, or be a “weekend warrior” getting in a longer, vigorous workouts when you can, said Bruellman.

He hopes the study will serve as a call to action for policymakers to revisit physical activity guidelines and specify how much sitting is too much.

Meanwhile, Reynolds encourages young adults to take steps now that could shape their future:

“This is the time to build habits that will benefit health over the long term.”