NDNS 65+ and other surveys calculated the
correlation coefficients
between the intake of many nutrients and its level in the blood
The degree of correlation between these two
was often less than
50% and is usually best for the more water-soluble and better absorbed nutrients
The reason for low correlation are many and
include: level of
intake, limited or poor absorption, smoking and alcohol, and differences in
metabolism/transport of the nutrient
In practice this means that clinicians should
not rely too heavily
on dietary assessment but consider many other risk factors for under and overnutrition