If you sign in with your Apple ID, your health and fitness information in the Health app 
is stored automatically in iCloud. Your information is encrypted as it goes between iCloud and your device and while it’s stored in iCloud.
In addition to using iCloud, or if you aren’t using iCloud, you can back up your Health data by encrypting a computer backup. See Back up iPhone.
Stop storing your Health data in iCloud
Go to Settings 
> [your name] > iCloud, then turn off Health.