If confirmed, the finding may mean it's a good idea to routinely track blood pressure in premature babies, write the researchers.
They included Stefan Johansson, MD, of Sweden's Karolinska Institute. Johansson is a neonatologist -- a specialist in caring for newborns.
The study appears in Circulation.
Early Birth and Blood Pressure
Johansson's team checked the birth records and blood pressure of more than 329,000 young Swedish men when the men were drafted for Sweden's military. Many of the men had high blood pressure.
Take systolic blood pressure, for example. That's the first number in a blood pressure reading when the heart pumps blood out. Elevation in blood pressure makes the heart work harder and increases the risk of heart attacks and heart failure. High blood pressure also increases the risk of diseases such as kidney disease, stroke, and eye damage.
One in five men had high systolic blood pressure, the study shows. Those who had been born early were more likely to be in that group.
The earlier the men had been born, the greater their odds of having high systolic blood pressure.
Men who had been born extremely early (24-28 weeks) were nearly twice as likely to have high systolic blood pressure as young adults, compared with those who had been born at full term (37-41 weeks).
Patterns weren't as strong for preterm birth and diastolic blood pressure (the second number in a blood pressure reading).
The study doesn't explain why premature babies might be more likely to have blood pressure later in life.
Social class, maternal factors, and health around the time of birth were taken into account.
No women were studied, so the results might not extend to baby girls, the researchers note.
Protection From Breast Milk?
Breast milk might offer some blood pressure advantages for premature babies, note Johansson and colleagues.
They cite a study published by other researchers in 2001. That study looked at blood pressure in teens who had been born prematurely.
Those who had been breastfed as babies had lower blood pressure as teens, compared with those who had been fed formula.
The topic needs more study but perhaps "the risk for high blood pressure in adults born preterm could already be modulated in the neonatal nursery," writes Johansson's team.