If you would no longer like share health data with someone you can remove them as a connection through the following steps:
Tap the "More" menu at the bottom navigation bar.
Tap the "Connections" tab.
Tap the three dot icon at the top right of their profile card and click remove.
You and your connection will no longer have access to each others health data and will not see updates from each other in your pulse. This user will not be notified that you removed them as a connection.