Interpopulation and intrapopulation variability of nutrient intake in five regions of Japan

Objectives: To determine the extent to which interpopulation (between-population) variance, relative to intrapopulation (within-population) variance, contribute to the total variability in nutrient intakes. Design: Cross-sectional study. Setting: Five Public Health Center districts in Japan. Subjects: Two hundred and seven men and 183 spouses. Interventions: A three-day weighed food record. Main outcome measures: The total variance in the consumption of 17 nutrient variables was partitioned by analysis of variance into its inter- and intrapopulation components separately for men and women. Results: The percentage contribution of the interpopulation to total variance differed according to the nutrient; it was notable (8-17%) for total energy, carbohydrates, phosphorus, and sodium in both men and women, but was negligible (less than 4%) for micronutrients such as retinol, carotene, thiamin, riboflavin, niacin and ascorbic acid. The ratio of intra- to interpopulation variance was estimated for 31 nutrients (17 in men and 14 in women). The point estimates of the ratio were larger than unity in all nutrients, and the lower limit of the 95% confidence intervals exceeded unity for all but 5 nutrients. Of the two sources of intrapopulation variation, intraindividual variance was larger than interindividual variance in most of the nutrient. Conclusions: The relative magnitude of interpopulation variation in dietary data can be used to quantify the range of exposure in ecological studies and to examine the heterogeneity of populations pooled for individual-based analysis