Facebook already knows who your friends are and the kind of things that grab your attention. Soon, it could also know the state of your health. On the heels of fellow Silicon Valley technology companies Apple and Google, Facebook is plotting its first steps into the fertile field of healthcare, said three people familiar with the matter. The people requested anonymity as the plans are still in development. The company is exploring creating online “support communities” that would connect Facebook users suffering from various ailments. A small team is also considering new “preventative care” applications that would help people improve their lifestyles. In recent months, the sources said, the social networking giant has been holding meetings with medical industry experts and entrepreneurs, and is setting up a research and development unit to test new health apps. Facebook is still in the idea-gathering stage, the people said.