Policy Research for Front of Package Nutrition Labeling: Developing and Testing a Summary System Algorithm. 4.4.1 Correlation Analyses to Inform Development of a New Approach

05/01/2011

We conducted correlation analyses using SAS Proc Corr with day 1 dietary weights with variables representing the nutrient intakes as a percentage of recommended intake levels per 100 kcal consumed for the 17 nutrients/components and the HEI scores of individuals in NHANES. The inclusion in the model of nutrients that are highly correlated with each other may not provide more information to the prediction of dietary quality than if only one of the nutrients was included. The correlation coefficients are provided in Table 4-2.


Table 4-2. Correlation Matrix of Nutrient or Component Intakes as a Percentage of Recommended Intake Levels Per 100 Kcal and HEI Scorea
Nutrient/
Component
HEI Protein Fiber Vitamin
E
Vitamin
D
Calcium Iron Potas-
sium
Unsatu-
rated
Fat
Magne-
sium
Vitamin
A
Vitamin
C
Folic
Acid
Vitamin
B12
Satu-
rated
Fat
Sodium Added
Sugar
Whole
Grains
(% of
Whole)
a Nutrient intakes and HEI scores are from 1-day dietary intakes for 16,587 participants in NHANES 2005-2008.
- Means no data.
HEI 1.00 0.33 0.60 0.35 0.22 0.21 0.32 0.50 0.04 0.52 0.29 0.42 0.16 0.14 −0.40 −0.02 −0.39 0.35
Protein - 1.00 0.16 0.09 0.29 0.27 0.26 0.42 0.03 0.36 0.23 0.09 0.01 0.39 0.07 0.35 −0.45 0.09
Fiber - - 1.00 0.32 0.05 0.16 0.37 0.53 −0.07 0.60 0.31 0.41 0.14 0.03 −0.26 0.10 −0.32 0.36
Vitamin E - - - 1.00 0.04 0.08 0.22 0.25 0.28 0.37 0.28 0.29 0.08 0.11 −0.11 0.06 −0.22 0.09
Vitamin D - - - - 1.00 0.62 0.27 0.33 −0.16 0.25 0.44 0.13 0.26 0.61 0.05 −0.04 −0.13 0.17
Calcium - - - - - 1.00 0.25 0.36 −0.21 0.43 0.45 0.21 0.24 0.41 0.17 0.06 −0.22 0.23
Iron - - - - - - 1.00 0.26 −0.16 0.35 0.42 0.21 0.70 0.50 −0.20 0.16 −0.18 0.34
Potassium - - - - - - - 1.00 −0.13 0.71 0.38 0.47 −0.02 0.25 −0.14 0.15 −0.39 0.22
Unsaturated fat - - - - - - - - 1.00 −0.10 −0.11 −0.17 −0.23 −0.13 0.38 0.15 −0.29 −0.09
Magnesium - - - - - - - - - 1.00 0.37 0.33 0.07 0.19 −0.23 0.11 −0.39 0.34
Vitamin A - - - - - - - - - - 1.00 0.30 0.27 0.38 0.02 0.07 −0.16 0.25
Vitamin C - - - - - - - - - - - 1.00 0.08 0.08 −0.24 0.01 −0.16 0.17
Folic acid - - - - - - - - - - - - 1.00 0.40 −0.16 0.06 −0.07 0.25
Vitamin B12 - - - - - - - - - - - - - 1.00 0.09 0.06 −0.13 0.14
Saturated fat - - - - - - - - - - - - - - 1.00 0.08 −0.17 −0.10
Sodium - - - - - - - - - - - - - - - 1.00 −0.32 0.00
Added sugar - - - - - - - - - - - - - - - - 1.00 −0.13
Whole grains - - - - - - - - - - - - - - - - - 1.00

These results show that calcium and vitamin D are highly correlated (r = 0.62). Dairy foods are primary sources of both calcium and vitamin D to the daily diet, and some fish are high in both of these nutrients. Folic acid is highly correlated with iron (r = 0.70), so the algorithm that included folic acid may not have improved the prediction of HEI over the baseline algorithm because of the collinearity with iron, which is likely due to fortification of grains with both folate and iron. Magnesium is strongly correlated with potassium (r = 0.71), so the addition of magnesium to the baseline algorithm that contained potassium may not have added to the explanation of dietary quality. HEI is strongly correlated with fiber (r = 0.60), magnesium (r = 0.52), potassium (r = 0.50), vitamin C (r = 0.42), saturated fat (r = −0.40), added sugar (r = −0.39), vitamin E (r = 0.35), and whole grains (r = 0.35).