Vitamine Machine

  Have you seen the diabetic PDA machine that measures the amount of insulin in the blood by a body suction cap thingi.
  I think a derivitive of that machine that could measure the amount of vitamins and minerals in your blood and say if you've have an overdose of vitamin C or you need more vitamin C today. This would help anemic people and everybody in general keep track on what they're eating and what they need to be eating.
  How do we know if we got the right doses of vitamins and minierals today.