Smartwatches track health changes but cannot predict disease, doctors say

Smartwatches and fitness bands can watch your body while you sleep, checking your heartbeat, breathing and how much oxygen is in your blood.

They can notice when something changes, like a funny heartbeat or trouble sleeping.

Sometimes they help people visit a doctor before they feel sick.

But a smartwatch is not a doctor and cannot tell you for sure if you have a disease.

Predicting disease needs blood tests, family history and a real doctor's judgment.

The little heart-reading on a watch is also not as good as the big machines used at hospitals.

Readings can be wrong if the watch is loose or you move around a lot.

That's why doctors say you should look at changes over many days instead of one single number.

Wearables are helpers that work alongside doctors, not replacements for them.