People with BMIs between 19 and 22 live longest

People with BMIs between 19 and 22 live longest say the BBC. Death rates are noticeably higher for people with indexes 25 and above (see link). Where is the evidence for this in the Scientific Literature? (source: Christopher Govan Street).

I'm 5'7.5" height so my BMI are:

• BMI 27.5 = 12st 8lbs (weight @ 24/12/06)
• BM1 24 = 11st 1lb (my target)
  
• BMI 22 = 10 st
• BMI 21 = 9 st 8lbs
  
• BMI 18.6 = 9 st
  

(Source: Calculator)

The World Health Organization (WHO) says there is evidence that risk of chronic disease in populations increases progressively from a BMI of 21.

In the analyses carried out for World Health Report 2002, approximately 58% of diabetes and 21% of ischaemic heart disease and 8-42% of certain cancers globally were attributable to a BMI above 21kg/m2. This report says "Disease relationships were evident with increases in adult BMIs above 21".

A BMI of 25 to 29.9 is considered overweight and one 30 or above is considered obese.

The BMI is not infallible. For instance, it is possible for a healthy, muscular athlete with very low body fat to be classified obese using the BMI formula. If you are a trained athlete, your weight based on your measured percent body fat would be a better indicator of what you should weigh.