Low iron status as a factor of increased bone resorption and effects of an iron and vitamin D-fortified skimmed milk on bone remodelling in young Spanish women

Purpose

This study aimed to determine whether there is a relationship between iron status and bone metabolism, and to compare the effects of the consumption, as part of the usual diet, of an iron or iron and vitamin D-fortified skimmed milk on bone remodelling in iron-deficient women.

Methods

Young healthy iron-deficient or iron-sufficient women (serum ferritin ≤30 ng/mL or >30 ng/mL, respectively) were recruited. Iron-deficient women were assigned to a nutritional intervention consisting of a randomised, controlled, double-blind, parallel design trial of 16 weeks during winter. They consumed, as part of their usual diet, an iron (Fe group, n = 54) or iron and vitamin D-fortified (Fe+D group, n = 55) flavoured skimmed milk (iron, 15 mg/day; vitamin D₃, 5 μg/day, 200 IU). The iron-sufficient women followed their usual diet without supplementation (R group, n = 56). Dietary intake, body weight, iron biomarkers, 25-hydroxyvitamin D (25OHD), parathyroid hormone (PTH), procollagen-type 1 N-terminal propeptide (P1NP), and aminoterminal telopeptide of collagen I (NTx) were determined.

Results

Negative correlations were found between baseline log-ferritin and log-NTx (p < 0.001), and between transferrin and P1NP (p = 0.002). Serum 25OHD increased (from 62 ± 21 to 71 ± 21 nmol/L, mean ± SD, p < 0.001) while P1NP and NTx decreased in Fe+D during the assay (p = 0.004 and p < 0.001, respectively). NTx was lower in Fe+D compared to Fe at week 8 (p < 0.05) and was higher in Fe and Fe+D compared to R throughout the assay (p < 0.01). PTH did not show changes.

Conclusions

Iron deficiency is related with higher bone resorption in young women. Consumption of a dairy product that supplies 5 μg/day of vitamin D₃ reduces bone turnover and increases circulating 25OHD to nearly reach an optimal vitamin D status, defined as 25OHD over 75 nmol/L.