Elderly Chinese parents become U.S. Citizen

Both of my parents are in their early 70s' and they retired in China years ago and have been receiving their Chinese pension including full medical care benefit. They have U.S. Green Cards and have been living in the U.S. for the past 5 years. If they become U.S. Citizen, I understand that they will automatically lose their Chinese citizenship; but will they also lose their Chinese pension and medical coverage? Thank you!