It would be so fantastic if we could just have a chip implanted to continuously measure this stuff, then download it and analyze on a daily, weekly, monthly and annual basis. There's so much cool science to be done here, especially if this is done on a global scale.

Yes. There are common panels available at Quest/Labcorp that will measure critical nutrients such as Vitamin D or Vitamin B12. In addition, there is a more comprehensive test called ION available from Metametrix.