Bone and fat mass in relation to postnatal levels of insulin-like growth factors in prematurely born children at 4 y of age

Abstract

Background: Children born prematurely may be at risk of developing osteopenia. This study investigated whether insulin-like growth factors (IGFs) in the early postnatal period influence bone mass and body composition in prematurely born children. Methods: A total of 74 control (gestational age >36 wk; n = 37) and preterm (gestational age <32 wk; n = 37) infants were investigated (mean age ± SD: 4.59 ± 0.31 y). Bone mineral density, body composition, and markers of bone and mineral metabolism were investigated in relation to postnatal IGF levels. results: After adjusting for confounders, we found no differences in bone mass, but significantly less lean mass, increased fat mass, and increased osteocalcin levels in ex-preterm infants. Forward stepwise multiple analysis revealed that higher late postnatal IGF-II levels predict lumbar spine bone mineral content (P < 0.05) and lean mass (P < 0.05). When the birth weight standard deviation score was included in the analysis, higher early postnatal IGF-I levels predicted both lumbar spine bone mineral density and bone mineral content (P < 0.05). Higher early postnatal IGF binding protein-3 (P < 0.01) predicted increased fat mass at 4-y follow-up. conclusion: Ex-preterm children have normal bone mass but different body composition compared with full-term controls. Higher early IGF-I and late postnatal IGF-II concentrations are positive predictors of lumbar spine bone mass. c hildren's bone health is an important issue with lifelong importance. Many factors and medical conditions are associated with an increased risk of a bone mineral disorder and future skeletal problems, including genetics, mechanical loading, activity level, longitudinal growth, puberty, hormones, cytokines, and nutritional status. Peak bone mass is achieved during early adulthood and serves as the "bone bank" for the remainder of life. Bone remodeling, the continuous process of bone formation and resorption, can be assessed and monitored by biochemical markers of bone turnover (1). Many studies have found that ex-preterm infants are shorter, lighter, and have lower bone mass (2-5) than their full-term peers, and ex-preterm infants who are small for gestational age at birth seem to have the most risk (6). However, several studies have found that the bone mass in ex-preterm infants is appropriate for their body size (7,8) and one study proposed that bone mineral density (BMD) in very-low-birth-weight infants is normalized at 2 y of age (9). During adolescence, children who were born prematurely do not have different bone mineral content (BMC ) (10) or BMD (11) (adjusted for height and weight) in comparison with normal-weight children born at full term. Supplementation with early diet benefits short-time growth and BMD. Positive outcomes of an early special diet have been shown on body composition and fat mass during the first 2 y of life, but the long-term effects on BMD and other morbidities are not yet known (12).In full-term newborn infants, umbilical cord serum insulinlike growth factor (IGF)-I and ...

Dietary proteins and IGF I levels in preterm infants: determinants of growth, body composition, and neurodevelopment

“…In addition, 20 y olds who were born preterm, especially those small for gestational age, had decreased bone mineral density and were shorter compared to term controls (35,36). Interestingly, however, others found normal bone mass in 4-yold children who were born preterm (9). As stated by Stigson et al, osteoblasts as well as adipocytes are derived from the same progenitor cells and the IGF system could be important in directing the differentiation to either adipocytes or osteoblasts (9).…”

“…Indeed, in small for gestational age very low birth weight infants IGF I levels up to 3 mo corrected age have been positively associated with lean mass at 2 y (30). Moreover, preterms were found to have increased fat mass and decreased lean mass in childhood (9). However, a recent meta-analysis could not confirm that this trend persists into adulthood (31).…”

“…Interestingly, however, others found normal bone mass in 4-yold children who were born preterm (9). As stated by Stigson et al, osteoblasts as well as adipocytes are derived from the same progenitor cells and the IGF system could be important in directing the differentiation to either adipocytes or osteoblasts (9). It may well be that states with low IGF I levels, such as critical illness, nutrient restriction and extreme prematurity, stimulate differentiation towards adipogenesis as a mechanism to ensure an easily accessible energy store, in this relatively catabolic state, as compared to anabolic states with high IGF I levels where sustainable growth through bone formation might be obtained.…”

“…Surely, IGF I is involved in bone accretion, but it is also implied in adipogenesis (32,33). Indeed Stigson et al found that higher IGF I levels at a postmenstrual age of 30-32 wk were associated with increased bone mass (9). Also, a trend of higher IGF I levels was found in preterm infants who increased in bone strength compared to preterm infants with a decrease in bone strength measured by bone speed of sound (34).…”

“…Furthermore, preterm infants are prone to develop risk factors for the onset of the metabolic syndrome. They are reported to have lower insulin sensitivity, increased blood pressure and increased fat mass in childhood and young adulthood (7)(8)(9). Nutritional interventions in these infants have been found to influence the development of risk factors for the metabolic syndrome (10).…”