Osteoporosis causes bones to become fragile and more prone to break. The disease is much more common in women than men.
Now a study in the Journal of Adolescent Health finds girls who smoke put themselves at an even greater disadvantage.
Scientists found, over time, that girls who smoke have decreased bone density, which could lead to an increased risk of osteoporosis later in life.
Women start with lower bone density than men and they lose bone mass more quickly as they age.
Researchers say teens shouldn't give the process a head start by smoking.