Adjustment of directly measured adipose tissue volume in infants

The mysterious values of adipose tissue density and fat content in infants: MRI-measured body composition studies

Adipose tissue is a type of connective tissue composed of closely packed adipocytes with collagenous and elastic fibers. These adipocytes store triglycerides at a high percentage and the estimate of this amount is important for the calculation of body fat mass. For example, magnetic resonance imaging (MRI) measures adipose tissue volume, but adipose tissue density (fat content percentage and density) is required to calculate fat mass. However, in previously published studies, the conversion factor for white adipose tissue density varies from study to study. This paper aimed to investigate the different adipose tissue densities used as conversion factors to clarify differences between studies. Furthermore, we include a new proposal for adipose tissue density and fat content of infants based on the results of recent water-fat MRI studies. IMPACT: Magnetic resonance imaging (MRI) is one of the methods used to measure body composition in infants and the inherent density of tissue/organs is needed in order to calculate the mass of target organs and tissues. The conversion factor used for white adipose tissue density currently varies from study to study. This article includes a new recommendation for the adipose tissue density and fat content of infants based on the results of recent water-fat MRI studies.

The association between neck adiposity and long-term outcome

Anthropometric indices of obesity (e.g. body mass index, waist circumference and neck circumference) are associated with poor long-term cardiovascular outcome. Prior studies have associated neck circumference and central body adiposity. We explored the association between neck fat volume (NFV) and long-term cardiovascular outcome. The study provides a retrospective analysis of all patients undergoing computerized tomography angiography for suspected cerebrovascular accident between January and December 2013. NFV was assessed by three dimensional reconstructions and was adjusted to height to account for differences in body sizes, thus yielding the NFV/height ratio (NHR). Univariate and multivariate analysis were utilized to explore the association between various indices including NHR and all-cause mortality. The analysis included 302 patients. The average age was 61.9±14.3 years, 60.6% of male gender. Diabetes mellitus, hypertension and cardiovascular disease were frequent in 31.5%, 69.9%, and 72.2% of patients, respectively. The median NHR was 492.53cm² [IQR 393.93–607.82]. Median follow up time was 41.2 months, during which 40 patients (13.2%) died. Multivariate analysis adjusting for age, sex, and diabetes mellitus indicated an independent association between the upper quartile of NHR and all-cause mortality (hazard ratio = 2.279; 95% CI = 1.209–4.299; p = .011). NHR is a readily available anthropometric index which significantly correlated with poor long-term outcome. Following validation in larger scale studies, this index may serve a risk stratifying tool for cardiovascular disease and future outcome.

Body Composition following Necrotising Enterocolitis in Preterm Infants

BACKGROUND

The optimal nutritional regimen for preterm infants, including those that develop necrotising enterocolitis (NEC), is unknown.

OBJECTIVE

The objective here was to evaluate body composition at term in infants following NEC, in comparison with healthy infants. The primary outcome measure was non-adipose tissue mass (non-ATM).

METHODS

We compared body composition assessed by magnetic resonance imaging at term in infants born <31 weeks of gestational age that participated in NEON, a trial comparing incremental versus immediate delivery of parenteral amino acids on non-ATM, and SMOF versus intralipid on intrahepatocellular lipid content. There were no differences in the primary outcomes. We compared infants that received surgery for NEC (NEC-surgical), infants with medically managed NEC (NEC-medical), and infants without NEC (reference).

RESULTS

A total of 133 infants were included (8 NEC-surgical; 15 NEC-medical; 110 reference). In comparison with the reference group, infants in the NEC-surgical and NEC-medical groups were significantly lighter [adjusted mean difference (95% CI) NEC-surgical: -630 g (-1,010, -210), p = 0.003; NEC-medical: -440 g (-760, -110), p = 0.009] and the total adipose tissue volume (ATV) was significantly lower [NEC-surgical: -360 cm3 (-516, -204), p < 0.001; NEC-medical: -127 cm3 (-251, -4); p = 0.043]. There were no significant differences in non-ATM [adjusted mean difference (95% CI) NEC-surgical: -46 g (-281, 189), p = 0.70; NEC-medical: -122 g (-308, 63), p = 0.20].

CONCLUSION

The lower weight at term in preterm infants following surgically and medically managed NEC, in comparison to preterm infants that did not develop the disease, was secondary to a reduction in ATV. This suggests that the nutritional regimen received was adequate to preserve non-ATM but not to support the normal third-trimester deposition of adipose tissue in preterm infants.

Development of Early Adiposity in Infants of Mothers With Gestational Diabetes Mellitus

OBJECTIVE

Infants born to mothers with gestational diabetes mellitus (GDM) are at greater risk of later adverse metabolic health. We examined plausible candidate mediators, adipose tissue (AT) quantity and distribution and intrahepatocellular lipid (IHCL) content, comparing infants of mothers with GDM and without GDM (control group) over the first 3 postnatal months.

RESEARCH DESIGN AND METHODS

We conducted a prospective longitudinal study using MRI and spectroscopy to quantify whole-body and regional AT volumes, and IHCL content, within 2 weeks and 8-12 weeks after birth. We adjusted for infant size and sex and maternal prepregnancy BMI. Values are reported as the mean difference (95% CI).

RESULTS

We recruited 86 infants (GDM group 42 infants; control group 44 infants). Mothers with GDM had good pregnancy glycemic control. Infants were predominantly breast-fed up to the time of the second assessment (GDM group 71%; control group 74%). Total AT volumes were similar in the GDM group compared with the control group at a median age of 11 days (-28 cm(3) [95% CI -121, 65], P = 0.55), but were greater in the GDM group at a median age of 10 weeks (247 cm(3) [56, 439], P = 0.01). After adjustment for size, the GDM group had significantly greater total AT volume at 10 weeks than control group infants (16.0% [6.0, 27.1], P = 0.002). AT distribution and IHCL content were not significantly different at either time point.

CONCLUSIONS

Adiposity in GDM infants is amplified in early infancy, despite good maternal glycemic control and predominant breast-feeding, suggesting a potential causal pathway to later adverse metabolic health. Reduction in postnatal adiposity may be a therapeutic target to reduce later health risks.

Sexual dimorphism in relation to adipose tissue and intrahepatocellular lipid deposition in early infancy

Sexual dimorphism in adiposity is well described in adults, but the age at which differences first manifest is uncertain. Using a prospective cohort, we describe longitudinal changes in directly measured adiposity and intrahepatocellular lipid (IHCL) in relation to sex in healthy term infants. At median ages of 13 and 63 days, infants underwent quantification of adipose tissue depots by whole-body magnetic resonance imaging and measurement of IHCL by in vivo proton magnetic resonance spectroscopy. Longitudinal data were obtained from 70 infants (40 boys and 30 girls). In the neonatal period girls are more adipose in relation to body size than boys. At follow-up (median age 63 days), girls remained significantly more adipose. The greater relative adiposity that characterises girls is explained by more subcutaneous adipose tissue and this becomes increasingly apparent by follow-up. No significant sex differences were seen in IHCL. Sex-specific differences in infant adipose tissue distribution are in keeping with those described in later life, and suggest that sexual dimorphism in adiposity is established in early infancy.