Potassium balance in cows is the result of potassium intake, distribution in the organism, and excretion, and it is closely related to glucose and electrolyte metabolism.
Energy intake, distribution of macronutrients and two variety scores were calculated from 3-day weighed dietary records.
All analysis used SAS software (Version 9.4 of SAS System for Windows, SAS Institute, Cary, NC, 2013) and estimates of the usual intake distribution used macros, code and methods adapted from NCI and the Centers for Disease Control CDCC) [ 28, 29].
Categories were determined by usual serving size (as defined above) from the FFQ and the intake distribution for all subjects.
Sodium intake distribution (median, 25th percentile (P25) and 75th percentile (P75)) was calculated for the current food consumption pattern and for both scenarios by summing the sodium levels in foods per subject per observation day and by dividing it by the number of observation days (that is, 2).
The usual intake distribution for each nutrient was determined and compared with the EAR and UL.
Simply adding the amounts taken from dietary supplements to the intake from foods prior to statistical correction for within-person variation may result in lower intake estimates at the low percentiles of the intake distribution for the intake from food and dietary supplements compared with the intake from food only.
A repeat urine sample, collected from a subset of women, in each trimester would have given a better estimate of usual intake for the group (by correcting for intraindividual variation and adjusting the intake distribution to the mean) (56); unfortunately, repeat measures within a trimester were not available.
The large intra-subject variance in folate intakes were removed using SIDE: Software for Intake Distribution Estimation (version 1.0, Dept of Statistics and Center for Agricultural and Rural Development, Iowa State University, Iowa).
The FFQ was validated in a subset of controls using 12-monthly 24-h dietary recalls as the reference method, and the percentages of women classified in the same ±1 quartile of intake distribution by both methods were 74% for total energy and 85, 96 and 90% for energy-adjusted fat, carbohydrates, protein and NSP, respectively (Sevak et al, in press).
