This may boost their risk of the bone-thinning disease osteoporosis in adulthood, the study team notes.
Dr. Petteri Hovi, of the National Institute for Health and Welfare, Helsinki and colleagues studied 144 Finnish adults who were born prematurely (after an average of 29 weeks instead of the normal 40 weeks) weighing less than 1,500 grams (3.3 pounds).
They compared the bone health of these individuals with that of 139 age- and sex-matched adults who were born at term at a normal weight (about 7 pounds 11 oz).
At an average age of 22.6 years -- close to the age of peak bone mass -- the researchers measured bone mineral density (BMD) in the lower back and the hip in all of the study subjects.
According to a report in the journal PLoS Medicine, the young adults who were born prematurely had less dense bones (lower BMD) at both the lower back and hip when compared with adults born at term.
The former premmies also had a twofold greater risk of having BMD in the range that roughly doubles their risk of bone fractures.
In an email to Reuters Health, Hovi said people who were born prematurely with low birth weight "may be able to reduce their risk of developing osteoporosis by eating a diet rich in calcium and vitamin D and performing weight bearing exercise regularly."