Apple Health is the health data platform built into every iPhone and iPad. It acts as a central repository for health and fitness data from your Apple Watch, third-party wearables, and manual entries.
Device compatibility through Apple Health
Different devices provide different biomarkers when syncing through Apple Health. Here's what you can expect:
Device type | RHR | HRV | VO2max | LBMI | Activity | Sleep |
Apple Watch | ✓ | ✓ | ✓ | — | ✓ | ✓ |
Garmin | ✓ | ✗ | ✗ | — | ✓ | ✓ |
Oura | ✓ | ✗ | ✗ | — | ✓ | ✓ |
Fitbit | ✓ | ✗ | ✗ | — | ✓ | ✓ |
Polar | ✓ | ✗ | ✗ | — | ✓ | ✓ |
Whoop | ✓ | ✗ | ✗ | — | ✓ | ✓ |
Smart scales | — | — | — | ✓ | — | — |
Manual entry | ✓ | ✓ | ✓ | ✓ | — | — |
Legend: ✓ Supported | ✗ Not supported | — Not applicable
Why the differences?
Apple Health uses SDNN (standard deviation of NN intervals) as its HRV measurement standard. Most third-party wearables calculate HRV differently and don't write SDNN values to Apple Health, which is why only Apple Watch provides HRV through Apple Health.
Similarly, most wearables don't write VO2max estimates to Apple Health, even though they may calculate it in their own apps.
For complete and automatic True Age tracking through Apple Health, you need:
Apple Watch + Smart scale
Any wearable + Smart scale + manual entry for missing metrics
Wait for direct integrations (coming soon) to unlock all biomarkers from other devices
What data reThrive reads
reThrive reads the following data types from Apple Health to calculate your True Age, Pace of Aging, and upcoming Levers:
Heart health
Resting heart rate
Heart rate variability (HRV)
VO2max (cardio fitness)
Body composition
Lean body mass or Weight and Body fat percentage
Height
Activity and movement
Steps
Walking and running distance
Active energy burned
Exercise minutes
Workout sessions
Sleep
Sleep duration
Sleep stages (if available)
reThrive only reads this data. We never write data back to Apple Health or share it with third parties.
Manual data entry
Apple Health allows you to manually enter almost any health metric. This is useful if you don't have devices that automatically track certain data, or if you want to add measurements from other sources.
What's most useful to enter manually
For reThrive, these metrics are most valuable to enter by hand:
Body composition (for LBMI)
Lean body mass or Weight and Body fat percentage
Height
You can also fill in any gaps you might have in other metrics.
Heart health (for True Age)
Resting heart rate
HRV
VO2max
Note that wearables provide more consistent and frequent measurements for heart metrics. Manual entry works best for body composition, where weekly measurements are sufficient.
How to add manual data
Open the Health app on your iPhone
Tap Browse at the bottom
Select a category (e.g., Body Measurements)
Choose the specific data type (e.g., Weight)
Tap Add Data in the top right
Enter your measurement and date
Tap Add
Once you add data to Apple Health, reThrive will read it on the next sync.
When manual entry makes sense
You have a basic scale: Enter weight and body fat percentage weekly to track LBMI trends.
You get lab measurements: Add body composition data from DEXA scans or InBody measurements.
You're waiting for a wearable: Start building your baseline data while your device ships.
Manual entry works, but automatic syncing from devices is more consistent and less prone to gaps in your data.
Managing permissions
View your current permissions
Open the Health app on your iPhone
Tap your profile picture in the top right
Tap Apps under Privacy
Select reThrive
Review which data types are enabled
Grant additional permissions
If reThrive needs access to additional data types:
Follow the steps above to view permissions
Toggle on any data types you want to share
Return to reThrive
Tap Sync now in Settings > Apple Health to pull the newly available data
Revoke permissions
You can revoke permissions at any time in the same location. Note that revoking permissions will prevent reThrive from calculating metrics that depend on that data.
Common issues
reThrive isn't seeing my data
Make sure:
Your wearable is syncing to Apple Health (open the Health app to check)
You've granted all necessary permissions in Health > Apps > reThrive
You've triggered a manual sync in reThrive Settings > Apple Health
My wearable doesn't sync to Apple Health
Most major wearables sync automatically:
Apple Watch syncs continuously
Third-party devices (Garmin, Oura, Fitbit, Polar, Withings) require their companion app to be installed and configured
Check your wearable's companion app to confirm Apple Health sync is enabled.
I changed devices and lost data
Apple Health data is tied to your iPhone, but reThrive stores your data on our servers. If you:
Set up a new iPhone, your historical data will automatically load from our servers. Remember to reconnect Apple Health to enable new data flow.
Switched from Android, your historical data will automatically load from our servers. Remember to connect Apple Health to enable new data flow.
We only delete data from our servers when it's deleted from Apple Health.