At a time when immigration is a hot-button issue, the American health care system is highly dependent on professionals born in other countries, an analysis of U.S. census data shows.

In 2016, roughly 17 percent of professionals in 24 medical fields — from optometrists to chiropractors to veterinarians — were foreign-born, and almost 5 percent of them were not U.S. citizens, according to the analysis published this week in the Journal of the American Medical Association. The analysis could not distinguish between professionals trained in their country of origin and those trained in the United States.

The rates were even higher for the most educated providers. About one in five pharmacists, one in four dentists, and 29 percent of physicians _ approaching one in three — were foreign-born.

Among one of the biggest occupational groups — psychiatric, nursing and home health aides — 23 percent were foreign-born.

“We rely very heavily in health care on those who were born abroad,” said lead author Anupam B. Jena, an economist and physician at Harvard Medical School. “That tells you what would happen if we had a policy that restricted skilled immigration.”

The fields with the smallest percentages of foreign-born professionals were audiologists (5.9 percent), veterinarians (7.3), nurse-anesthetists (8.4) and psychologists (9.5).

About 16 percent of nurses, optometrists, dietitians and dental assistants were born abroad. Asia was the most common region of birth, accounting for 6.4 percent of all U.S. health care professionals. Mexico and the Caribbean were next, accounting for nearly 5 percent.