Trendline is an iPhone app that reads Apple Health. Everything below assumes an iPhone; the destination for your weigh-ins is Apple Health, which Android does not run.
The shape of the pipeline
iHealth's scales talk to one app, iHealth MyVitals (iHealth Labs Inc.; 4.8 stars across 146K ratings when we checked). The App Store listing states the Apple Health side directly: "After authorization, you can sync your measurement data in this app to your Healthkit to conduct comprehensive health data monitoring and health management." So the pipeline is scale → MyVitals → Apple Health — the same three links as every brand on our smart-scale index, with one distinctive middle: iHealth's link runs through its cloud.
The account, plainly
This is the part the flagship brands get criticized for, and iHealth documents it without apology. The same listing: "By creating an iHealth account and connecting our devices, you'll be able to store data securely in the cloud." The vendor's own sync-troubleshooting article makes the dependency concrete: its first step is checking that you're signed in with the correct account — noting that "many users don't realize they created an extra account" — and it states that a stable Wi-Fi or mobile data connection "is required for syncing" (iHealth support). Older iHealth docs describe synced data being sent to "your iHealth cloud secure space" (support article). In short: your measurement history's primary home is an iHealth account on iHealth's servers, and the docs assume you have one.
Two more vendor-stated facts sharpen why the Apple Health copy matters. The troubleshooting article warns that once a measurement transfers from the device to the app "it is erased from the device and cannot be recovered," and that on iPhone, clearing cache or reinstalling the app "deletes all stored data" locally. A weigh-in that MyVitals has also written to Apple Health is exempt from all of that — once written, it belongs to your phone's health record, not to any account.
Turning Apple Health sync on
Unusually for this cluster, the enable path is vendor-documented, step by step (iHealth support, updated 2025):
Open iHealth MyVitals and tap Account in the lower right corner.
Under DATA, select Authorize 3rd Party Apps.
Choose Apple Health, tap it, then tap Authorize and confirm with Done.
The same article notes the connection is reversible from the same screen (the button reads Unauthorize once linked), and that Apple Health and Fitbit are the two integrations iHealth currently supports. iOS will present its standard permission sheet along the way; grant the categories you want written. The switches also live in Apple Health itself — profile icon → Apps → iHealth — and in iPhone Settings → Apps → Health → Data Access & Devices (Apple's guide).
What's documented to transfer — and what isn't
iHealth says "measurement data" syncs to Apple Health after authorization; nowhere we could find does it enumerate which data types. Weight is the safest expectation — it's the measurement the vendor names for its scales across its own materials, and it has an obvious Health type. iHealth's composition-capable scales estimate further values, and the vendor's profile FAQ notes body-composition scales use your profile details to calculate them (iHealth support) — but whether any composition value is written to Health is not vendor-documented, so we won't claim it. The iOS permission sheet at authorization time is your authoritative list: whatever types it names are what MyVitals can write on your install.
What lands where
| What MyVitals writes to Apple Health | What Apple Health can store | What Trendline reads from Health |
|---|---|---|
| Vendor-confirmed in general terms: "measurement data" syncs after authorization (App Store listing), with a documented enable path (support article). No official per-type list exists; expect weight, and check the iOS permission sheet for the rest. | Weight, BMI, body fat %, lean body mass, height, waist circumference. No types exist for body water, protein, visceral fat, or similar composition estimates. | Weight, body fat %, and lean body mass (height as context). BMI and waist are not imported — BMI is derivable, and neither carries trend information Trendline needs. |
When Trendline launches, it will also accept manual entries — including composition values Apple Health has no type for — so readings the cloud keeps to itself can still sit alongside your trend.
When sync stalls
iHealth publishes a general sync-troubleshooting sequence, and it starts where the architecture starts (vendor article): confirm you're signed in with the right account, confirm Bluetooth is on and the device paired, confirm the internet connection, restart the app, and replace weak batteries. It also warns against clearing cache or reinstalling on iPhone before a sync completes, because local data doesn't survive that.
For the Apple Health link specifically, iHealth's closest published fix is filed under its activity trackers, not its scales — we label it accordingly: open Apple Health, tap your profile picture, select Apps under Privacy, open iHealth, and make sure every data category is toggled on (vendor article). The permission-rebuild step generalizes to any HealthKit app; the article's device specifics don't. If readings exist in MyVitals but not in Health, permissions are the first suspect; if they never reached MyVitals, the problem is upstream of Health entirely.
And the boundary no vendor states for you: readings flow from the day you authorize, forward. iHealth does not document whether past measurements transfer to Apple Health when you first connect — so we don't claim it either way. If your MyVitals history predates the toggle, check Health after enabling rather than assuming.
Try the idea
Once a few weeks of weigh-ins are flowing — or while you're still untangling accounts — paste your readings into the free weight trend calculator. It runs in your browser, nothing uploads, and it draws a deliberately slower signal next to your raw measurements. Day-to-day variation is real without being informative; the slower line is the one worth watching.
Sources
- App Store: iHealth MyVitals (HealthKit statement, account and cloud description)
- iHealth support: how to authorize 3rd-party apps in MyVitals (iOS)
- iHealth support: why is some data missing or not syncing
- iHealth support: activity data is not being shared with Apple Health
- iHealth support: what is the iHealth MyVitals app
- Apple: view your health data on iPhone
Trendline is not affiliated with or endorsed by iHealth Labs. Vendor behaviors change; this page states what was verifiable against the sources above on July 20, 2026, and says so where the documentation runs out.