Patients with anorexia nervosa (AN) often develop complications such as impaired bone metabolism, increased fracture rate, kidney stones and chronic renal failure. The mechanisms behind such complications are not completely understood. Healthy adolescents have been reported to have higher parathyroid hormone (PTH) levels in comparison with pre-pubertal children and adults. Central measures of calcium and vitamin D metabolism are key in bone and kidney health. Therefore, 25-hydroxyvitamin D (25OHD) and PTH have been widely studied in patients with AN; however, previous studies have not accounted for age-specific reference ranges for PTH.

A study was thus conducted by investigators in Canada to investigate central measures of calcium and vitamin D metabolism in adolescents with newly diagnosed AN using age-specific reference ranges. It was also assessed whether any significant abnormalities required further study.

This cross-sectional study included 61 adolescents (mean age 15.2 ± 1.56 years) with newly diagnosed AN, referred to a tertiary center over a period of 2 years. Demographic, auxiological, and nutrient (vitamin D and calcium) intake data was collected for all the participants. Central measures of calcium and vitamin D metabolism were evaluated in blood and urine. PTH results were compared with age-specific reference ranges from the Canadian Laboratory Initiative on Pediatric Reference Intervals (CALIPER).

Nearly 35% of the cohort had low PTH levels. Serum calcium, phosphate and 25OHD were found within the reference range. PTH exhibited a significant negative and non-linear correlation with 25OHD with an inflection point at a 25OHD level of 100 nmol/l. Beyond this level, the association was no longer seen. According to the correlation analysis, there was no significant association between PTH and total or corrected serum calcium, urine calcium/creatinine (Ca/Cr) ratio, total dietary calcium intake, magnesium or Tanner staging.

PTH levels were found to be decreased in nearly one-third of adolescents with AN. This may explain a potential role for reduced PTH levels in the development of kidney stones and bone phenotype in AN patients.

Source: Lenherr-Taube N, Trajcevski K, Sochett E, Katzman DK. Low PTH Levels in Adolescents With Anorexia Nervosa. Front Pediatr. 2020 Mar 11;8:99.