This is contrary to what I recall reading previously, so I looked up some sources. One study says: “When people come to the United States, they are positively selected, so people coming here are usually younger and healthier,” Baluran said. “What researchers found is that the longer people [immigrants] stay in the U.S., their health begins to deteriorate; by the time [they] reach the second and third generation, the health advantage that immigrants have almost disappeared.”
https://asamnews.com/2021/12/23/immigrants-asians-live-healt...