Health by the Numbers

A while ago we got one of those little magazines you get from the doctor's office. It talked about the 5 numbers you need to keep track of and manage to live a healthy life (statistically speaking). Being a numbers guy, I liked the idea. I have lost the article but I rememeber the first 4:

1. Cholesterol panel: HDL (> 45) , LDL (<>
2. Blood-pressure (<>
3. Blood sugar (<100)
4. BMI (<>
5. ????

Any idea what the last one could be? Let me know if you think you know...