Combining nutrient intake from food/beverages and vitamin/mineral supplements.

BACKGROUND: To calculate total intake of a nutrient and estimate inadequate intake for a population, the amounts derived from food/beverages and from vitamin/mineral supplements must be combined. The two methods Statistics Canada has suggested present problems of interpretation. DATA AND METHODS: Data collected from 34,386 respondents to the 2004 Canadian Community Health Survey-Nutrition were used to compare four methods of combining nutrient intake from food/beverages and vitamin/mineral supplements: adding average intake from supplements to the 24-hour food/beverage recall and estimating the usual distribution in the population (Method 1); estimating usual individual intake from food? beverages and adding intake from supplements (Method 2); and dividing the population into supplement users and non-users and applying Method 1 or Method 2 and combining the estimates based on the percentages of users and non-users (Methods 3 and 4).
RESULTS: Interpretation problems arise with Methods 1 and 2; for example, the percentage of the population with inadequate intake of vitamin C and folate equivalents falls outside the expected minimum-maximum range. These interpretation problems are not observed with Methods 3 and 4.
INTERPRETATION: Interpretation problems that may arise in combining food and supplement intake of a given nutrient are overcome if the population is divided into supplement users and non-users before Method 1 or Method 2 is applied.