Good point about psychological issues that haven't been addressed. I'd hesitate to call it 100% though. Hypertension can cause it, and though that's largely controllable through lifestyle changes (lay off the booze/salt/caffeine/tobacco), some people are going to end up with frigged up blood pressure from factors beyond their control (e.g. child abuse, PTSD, etc causes hypertension that sticks around later in life). Toss those unlucky few under the 1%.