In case you haven’t heard it yet, a sedentary lifestyle is no good for you. Sitting all day — or even most of it — has been called the new smoking, putting a person at risk for various health problems later on in life, as they forgo physical activity for extra downtime. Adding to this already-solid evidence, a new study finds that teens who lead sedentary lives are more likely to have a low bone mineral density (BMD).

BMD, which is essentially bone health measured by the concentration of minerals like calcium in the bones, is crucial for fracture prevention. Lower mineral density usually leads to weaker bones, and therefore, a higher chance of breaking them.

While having a higher BMD is obviously good for teens and young adults, it’s even better for older adults, of whom one in three fall each year. For older adults, a higher BMD could prevent fractures, which mostly occur in the age group due to falls. But attaining a higher BMD must begin during young age, as growing older weakens bones in and of itself. “Bone mineral density is a strong predictor of future fracture risk,” said Dr. Anne Winther, of the Arctic University of Norway, Tromsø, in a statement.

Winther and colleagues looked at computer use only on weekends, when children weren’t in school, and had free time to do whatever they wanted. They took data from the 2010-2011 Fit Futures study, looking at information from 463 girls and 484 boys aged 15 to 18. The data included measures of BMD at the hip, femoral neck, and total body, as well as answers from interviews and questionnaires regarding screen time and other lifestyle factors.

They found that boys were most likely to spend time in front of their computers on weekends, and that as they spent more time sitting at their desks, their BMD continued to dip. What’s more, yet unsurprising, these boys were also more likely to have higher measures in body mass index (BMI). Meanwhile, girls seemed to benefit from additional screen time, as those who spent four to six hours in front of the computer had higher BMDs than those who spent less than 1.5 hours. These findings held true even when the researchers accounted for age, sexual maturation, BMI, leisure time physical activity, smoking, alcohol, and soda consumption.

“Our findings for girls are intriguing and definitely merit further exploration in other studies and population groups,” Winther said in the statement. “The findings for boys, on the other hand, clearly show that [a] sedentary lifestyle during adolescence can [have an] impact on BMD and thus compromise the acquisition of peak bone mass. This can have a negative impact in terms of osteoporosis and fracture risk later in life.”

Winther presented her findings on Friday at the World Congress on Osteoporosis, Osteoarthritis, and Musculoskeletal Diseases, held by the International Osteoporosis Foundation (IOF). In preparation for World Osteoporosis Day later this year, on October 20, the IOF is focusing on osteoporosis among men, who, as this study has shown, tend to be caught unaware of the dangers of neglecting bone health. Though the condition is typically seen as a “woman’s disease,” more men are being diagnosed with it due to longer life expectancies and lifestyle habits that increase their risk. Up to one in four men over 50 years old will break a bone because of osteoporosis, according to the National Osteoporosis Foundation.

Thus, improving bone health, and overall health in general, during youth is the only way to prevent ailments in old age. If you think you’re at risk of osteoporosis, you can take a one-minute risk test here.