Apple backs up your Health data in iCloud, if you enable it.
"Your data in the Health app is encrypted with keys protected by your passcode, and never leaves your device unless you choose to back it up or grant access to a third-party app. When you do choose to back up your Health data through iCloud, it is encrypted both in transit and on our servers."
"Your data in the Health app is encrypted with keys protected by your passcode, and never leaves your device unless you choose to back it up or grant access to a third-party app. When you do choose to back up your Health data through iCloud, it is encrypted both in transit and on our servers."
https://www.apple.com/privacy/privacy-built-in/