A new study finds more than 23% of home health, psychiatric and nursing aides were born outside the U.S., with nearly 9% non-citizens.

The research, based on U.S. Census data covering 164,000 healthcare professionals, was led by Anupam Jena, M.D., Ph.D., and Ruth L. Newhouse,  associate professor at Harvard Medical School.

Nearly 17% of health professionals were born outside the U.S. and about 5% are not American citizens.

“These proportions are notable not only among physicians, on which previously conducted studies have focused, but also among the majority of other healthcare occupations that are important for patient care,” Jena said in a letter published in JAMA in December.

Among pharmacists, 20% were born elsewhere, while 16% of registered nurses and 15% of licensed practical nurses were immigrants.

“The American healthcare system relies very heavily on individuals who were born in other countries,” Jena told Reuters. “Our research shows that skilled immigration from other countries is an important contributor to nearly every occupation within the broader healthcare industry.”