A Danish study of 12,000 female nurses found that those with physically demanding jobs and high blood pressure tripled their risk of developing heart disease.

The study defined high-activity jobs as those requiring standing, walking, lifting, carrying and other exertion. Moderately active jobs, by comparison, involved standing and walking.

The study demonstrated an association — not causation — between the more active workers, blood pressure and heart disease.

But lead author Karen Allesoe, a Ph.D. student at the University of Southern Denmark, theorized that routine lifting and carrying might be to blame.

“For nurses, physically demanding jobs may involve high-force demands during patient handling, or standing and walking all day with no time for breaks,” she wrote in a statement announcing the study’s inclusion in February’s European Journal of Preventive Cardiology.

The researchers said further study could determine which aspects of nursing and other jobs are most problematic and develop guidelines to limit lifting and hours worked for hypertensive women.