Intakes and main food sources of calcium for vegetarian and omnivorous New Zealand adolescent females
Background: Calcium is an essential mineral required to assist peak bone mass formation during adolescence. Calcium can only be obtained through the diet and is not widely spread throughout dietary sources with dairy products being the richest source. The last nationwide investigation of calcium intake data suggested that adolescent females were not meeting their calcium requirements, placing them at a high risk of developing osteoporosis in later life. Furthermore, vegetarian diets are becoming increasingly popular in this demographic group and, in some instances, can involve the limiting or avoidance of dairy products. The aim of the current study is to investigate the impact these food choices may have on dietary calcium adequacy and to provide updated data on the calcium intakes of adolescent females living in New Zealand. Objective: To investigate the current calcium intake and food sources of vegetarian and omnivorous New Zealand adolescent females aged 15 – 18 years. Design: A cross-sectional observational survey of female adolescents aged 15 to 18 years from eight different locations throughout New Zealand. Data was collected in two waves (February to April and July to September 2019). Questionnaires examining participant demographics, dietary intakes and habits (including vegetarianism) and dietary supplement use were self-administered via an online platform. Standing height and weight was measured by trained investigators to allow calculation of BMI z-scores. Dietary intake data was collected using 24-hr dietary recalls, completed on two separate occasions and entered into the dietary assessment software programme FoodWorks to calculate nutrient intakes. Usual calcium intakes were estimated using the multiple source method and the prevalence of inadequate calcium intakes calculated by the Estimated Average Requirement (EAR)-cut-point method. Results: The study recruited 279 participants, 79.1% were of NZEO ethnicity, 15.5% Maori, 9% Asian and 6% Pacific. Most participants self-reported as following an omnivorous food pattern (87.1%) while 12.9% self-reported as being vegetarian. The median (interquartile range) usual intake of dietary calcium for adolescent females was 711 (544, 925) mg/day. The prevalence of inadequate calcium intakes was high, with 84% of the study population not achieving the EAR for calcium. No difference in calcium intakes were identified between vegetarian and omnivorous diets. Almost all (97%) of vegetarian participants had inadequate calcium intakes, however, inadequate intakes were also prevalent among omnivore participants (83%). Milk was the greatest contributor to calcium intakes (17.4%) and participants who reported drinking milk more regularly, had higher mean usual calcium intakes. The type of milk consumed varied between omnivore and vegetarian participants with cow’s milk more commonly consumed by omnivore participants and plant-based milks by vegetarian participants (81% vs 67.7%) with both groups more likely to consume whole/full fat options (76.3%). Conclusion: These results suggest that calcium intakes of New Zealand adolescent females remain below recommended intakes, thereby increasing the risk of developing osteoporosis in later life. Milk remains the largest contributor of calcium to dietary calcium intake for both vegetarian and non-vegetarian adolescents. Following a vegetarian diet does not markedly increase the risk of inadequate calcium intakes in this sample population as the median usual calcium intakes were similar for both omnivore and vegetarian participants. The small number of vegetarian participants (12.9%) prevented examination of the calcium intakes of vegetarian participants who choose to exclude all milk and dairy products (vegans). Given the major contribution dairy makes to the calcium intakes of adolescent females, further investigation regarding the dietary sources of calcium for vegans is warranted.
Advisor: MacDonell, Sue
Degree Name: Master of Dietetics
Degree Discipline: Human Nutrition
Publisher: University of Otago
Keywords: New Zealand; Adolescent; Calcium; Teenage; Intake; Vegetarian; non-vegetarian; Omnivore; Meat; Sources; Requirements; Plant-based; fortification; Inadequate; intake; Osteoporosis; Peak; bone; mass; Homeostasis; Bioavailability
Research Type: Thesis