Is underweight associated with poorer diet, nutrient status, bone and cardiometabolic health, and school performance in Danish 8-11-year-olds?

Purpose: Underweight, i.e. low body mass index for age and sex, may indicate undernutrition, but despite high prevalence, this aspect is largely overlooked in children in high-income countries. We explored if dietary intake, nutrient status, body composition, bone mineralization, cardiometabolic markers and school performance differed in schoolchildren with underweight compared to normal- and overweight. Methods: We used cross-sectional data from 815 Danish 8-11-year-old children collected in 2011. Intake of foods, macronutrients and key micronutrients (vitamin D, vitamin B12, calcium, iron, zinc and selenium) was assessed by 7-day dietary records. Measurements included anthropometry, dual-energy X-ray absorptiometry and tests of attention and reading skills. Fasting blood samples were analyzed for biomarkers of iron, long-chain n-3 fatty acids and vitamin D status as well as blood lipids, insulin and growth markers. Results: Eighty-three (10.2%) children had underweight and were shown to have a lower intake of energy, red meat, protein and zinc and higher intake of added sugar than children with normal- and overweight. They also had higher fish intake relative to overweight, but blood biomarkers did not differ between groups. Children with underweight had lower fat percent and bone mineralization compared to peers with normalweight, but apart from lower insulin, they did not differ in overall cardiometabolic health or school performance. Conclusion: Although we found some differences in diet, there were no considerable differences in nutrient status, cardiometabolic health or school performance between children with underweight and their normalweight peers. However, the lower bone mineralization is a concern and needs further investigation.