Iodine intakes of vegetarian and non-vegetarian adolescent females

Abstract

Background: The New Zealand government mandated fortification of bread with iodised salt as a strategy to address the re-emergence of iodine deficiency. Studies conducted since the fortification of bread with iodised salt have reported adequate iodine status in New Zealand children and adults, however, no studies have focused on adolescents. Overseas research has found a higher risk of iodine deficiency in vegetarians compared to non-vegetarians, a dietary pattern becoming more common in New Zealand. Objective: To determine the iodine intake and adequacy of vegetarian and non-vegetarian adolescent females in New Zealand. To identify the percentage of female adolescents using iodised salt and major food sources contributing to usual iodine intake. Design: A cross-sectional study of 15-18 year old females living in eight centres throughout New Zealand. Iodine intake was determined using two 24-hour diet recalls, adjusted using Multiple Source Method (MSM) programme to determine usual intake. Diet recalls were entered into FoodWorks 9 to calculate iodine intake from diet alone, using the New Zealand Food Composition Tables. Iodine intake from iodised salt was ascertained using a question on iodised salt use during the 24-hour diet recall. Iodine from discretionary salt was estimated at 48 μg of iodine for participants who indicated iodised salt use. Diet recall data was used to assess major food sources of iodine while a dietary habits questionnaire assessed frequency consumption of food groups including iodine rich foods. Results: The majority of participants (n=250) identified as New Zealand European and other ethnicities (78%),while 16% identified as Māori and 6% identified as Asian and Pacific. Over half of the participants (65%) had a healthy BMI (i.e. BMI z-score ≥-2 and ≤1) while almost a quarter was overweight (23%). Of the 250 participants analysed, 31 were vegetarians and vegans. The iodine intake for all participants from diet alone was 82 μg/day and from diet plus iodised salt was 104 μg/day. The iodine intake from diet alone for non-vegetarians was 83 μg/day and for vegetarians was 80 μg/day; the mean (95% CI) difference between the groups was 2.9 (-9.0 to 14.8) μg/day. Almost half (45%) of participants used iodised salt. The mean iodine intake from diet plus iodised salt was 105 μg/day for non-vegetarians and 92 μg/day for vegetarians; the mean (95% CI) difference between the groups was 13 (-0.7 to 27.3) μg/day. The iodine intake from diet plus iodised salt was 126 μg/day in participants who used iodised salt and 85 μg/day in participants who did not use iodised salt. More than half (68%) of participants did not meet the Estimated Average Requirements (EAR) for iodine of 95 μg/day from dietary iodine only while 39% did not meet the EAR from dietary iodine plus iodised salt. Bread was the main contributor of dietary iodine intake, contributing 34% and 25% to dietary iodine intake in vegetarians and non-vegetarians, respectively. Other major food groups contributing to iodine intake in descending order include: grains and pasta, non-alcoholic beverages and milk. Conclusion: No difference was found between the iodine intakes of vegetarians and non-vegetarians adolescent females. The majority of female adolescents in New Zealand had insufficient iodine intake that did not meet the EAR. After including iodine from iodised salt to their diets, iodine intake improved showing that the use of iodised salt is an important factor for this sample of female New Zealand adolescents in order to obtain enough iodine from their diet.