Biomedical subjects

Jonathan C K Wells

Publications and source records attributed to Jonathan C K Wells.

27 records · Page 2Linked to original sources

PubMed2004

Prematurity and reduced body fatness at 8-12 y of age.

BACKGROUND: Increasing evidence suggests that body composition, an important factor influencing morbidity and mortality in adult life, might be programmed by early growth and nutrition. Children born preterm remain shorter and lighter than their term-born peers during childhood, but it is unclear whether the size difference is associated with altered body composition. OBJECTIVE: We tested the hypothesis that both fat mass (FM) and fat-free mass (FFM) are proportionately lower in children born preterm than in children born at term. DESIGN: A total of 497 children born preterm and 95 children born at term were studied at 8-12 y of age. Body composition was determined with the use of skinfold thicknesses and dual-energy X-ray absorptiometry (in 200 preterm and 95 term children). FM and FFM were normalized for height to give fat mass index (FMI) and fat-free mass index (FFMI), respectively. RESULTS: Children born preterm were significantly lighter than those born at term and had lower FM and FFM. However, FMI was significantly lower in preterm children, whereas FFMI was not. FMI was also significantly lower in boys than in girls and in children with higher activity levels. Additional data available for the preterm group showed no association between birth weight, gestational age, or neonatal diet and later FMI or FFMI. CONCLUSIONS: The smaller size of children born preterm than of children born at term is associated with lower FM but not FFM when normalized for height. We hypothesize that this could result in a reduction in the risk of obesity and related diseases during adult life.

Absorptiometry, Photon↗

PubMed2003

A new method for quantifying encephalization in the growing individual.

Here we describe a new method for quantifying encephalization in the growing individual and provide a worked example of the methods. The new method is based on the use of conditional SD scores derived from brain and body growth references. These encephalization SD scores control for age, sex and body size effects on brain size, and therefore, control for the confounds associated with allometry as well as growth differences between the brain and body and between the sexes. The methods also control for distribution skewness. Encephalization SD scores derived from pre- and post-natal data may be directly compared and changes in SD score over time assessed. These methods may be applied to a broad range of data where relative size during growth is to be quantified. Derived SD scores may also be applied to correlation and regression analyses where statistical relationships with other variables are of interest.

Aging↗

PubMed2003

The thrifty phenotype hypothesis: thrifty offspring or thrifty mother?

Medical research is increasingly focusing on the contribution of nutritional programming to disease in later life. Programming is a process whereby a stimulus during a critical window of time permanently affects subsequent structure, function or developmental schedule of the organism. The thrifty phenotype hypothesis is widely used to interpret such studies, with early growth restriction seen as adaptation to environmental deprivation. However, such permanent adjustment is less beneficial than maintaining flexibility so as to recover from early growth deficits if the environment improves. Thus, the existing thrifty phenotype hypothesis fails to explain why plasticity is lost so early in development in species with extended growth. One explanation is that the developing organism simply cannot maintain phenotypic plasticity throughout the period of organ growth. This article adds a life history perspective, arguing that programming of the offspring may in some species benefit maternal fitness more than it does that of individual offspring. Closing the critical window early in development allows the preservation of maternal strategy in offspring phenotype, which in humans benefits the mother by constraining offspring demand after weaning. The offspring gains by being buffered against environmental fluctuations during the most sensitive period of development, allowing coherent adaptation of organ growth to the state of the environment. The critical window is predicted to close when offspring physiology becomes independent of maternal physiology, the timing of which depends on offspring trait. Because placental nutrition and lactation buffer against short-term environmental fluctuations, maternal strategy is predicted to derive from long-term experience, encapsulated in maternal size and nutritional status. Such an approach implies that public health programmes for improving birth weight may be more effective if they target maternal development rather than nutrition during pregnancy. Equally, aggressive nutritional management of infants born small or pre-term may induce the very environmental fluctuations that are naturally softened by maternal nutrition.

Adaptation, Physiological↗

PubMed2003

Validity of six field and laboratory methods for measurement of body composition in boys.

OBJECTIVE: To determine the validity of the following six body composition methods against a reference method (three-component model): air displacement plethysmography (BODPOD); estimation from body density using BODPOD; skinfold thickness using the Slaughter equations; bioelectrical impedance, both leg-leg (TANITA) and hand-foot (Bodystat) approaches; and total body water. RESEARCH METHODS AND PROCEDURES: Forty-two healthy white 10- to 14-year-old boys (mean age, 12.9 +/- 1.0 years) were enrolled in this study. Measures of body fat percentage and body fat mass derived from the three-component model were used as the reference method. Validity of all of the other methods was assessed by comparison against the reference by calculation of biases and limits of agreement. RESULTS: Mean body fatness measured using the reference method was 16.4 +/- 11.6% and 8.7 +/- 7.0 kg. Estimates of fatness from total body water had the narrowest limits of agreement relative to the reference (+0.9 +/- 5.0% body fat; +0.5 +/- 2.9 kg fat mass). For all other methods tested, we observed large biases and very wide limits of agreement. DISCUSSION: This study suggests that the validity of newer field and laboratory methods for estimation of body composition is poor in adolescent boys. For applications where high accuracy of estimation at the individual level is essential, only reference methods would be acceptable.

Adolescent↗

PubMed2002

Thermal environment and human birth weight.

Human birth weight is known to be influenced by several factors, including maternal energy supply, maternal stature, disease status, smoking status and gestation length. This article proposes that the thermal environment may be a further factor influencing birth weight. Experimental animal studies demonstrate clear effects of thermal stress on placental function and birth weight, but may have limited relevance for humans due to between-species differences in pregnancy physiology. Observational studies suggest an inverse relationship between environmental temperature and birth weight within and between human populations. Variation in maternal size, body fatness, pregnancy weight gain and heat production is predicted to influence maternal thermoregulatory capacity, as are the size and composition of the foetus. These associations generate the hypothesis that low birth weight in hot environments may in part represent an adaptation to environmental heat stress.

Adaptation, Physiological↗

PubMed2002

Birth weight and environmental heat load: a between-population analysis.

Low birth weight, a major cause of infant morbidity and mortality, is caused by different factors in Western and developing-country populations. In addition to differing in terms of ethnicity, maternal size, maternal nutritional status, and disease load, developing-country and Western populations are also characterized by different environmental heat loads. Thermodynamic theory predicts that heat stress is mitigated by reduced size of both mother and offspring, and therefore generates the hypothesis that reduced birth weight may be an adaptation to environmental heat load. The aim of this study was to test the hypothesis that environmental heat load is associated with between-population variability in birth weight. Data on birth weight and thermal environment were obtained from the literature for 140 populations. Further data on several physical, social, and biological confounders were also collated. After adjusting for confounding factors, of which only maternal height and per capita gross domestic product were statistically significant, heat stress showed a significant inverse relationship with birth weight in 108 populations, accounting for an additional 9.6% of the between-population variance. Though based on data collected from more than one source, these results are consistent with the hypothesis that heat stress is inversely associated with birth weight, as previously reported for within-population studies. Further studies are needed to establish to what extent heat stress is a determinant of low birth weight in developing countries.

Adaptation, Physiological↗

PubMed2002

Growth and failure to thrive.

Monitoring of growth in early life is particularly important as growth is elastic and sensitive to environmental factors, especially nutrition. Deficits are unlikely to be recovered fully in a later period and early growth patterns contribute to many diseases of adulthood. Assessment of rate of growth, rather than attained size, is possible with today's charts and accurate measurement. Growth monitoring is important for recognition of failure to thrive and it is valuable as a proxy measure for wellbeing. Many factors can contribute to failure to thrive which is best managed using a multidisciplinary approach.

Body Height↗

PubMed2002

Energy requirements and body composition in stable pediatric intensive care patients receiving ventilatory support.

Energy requirements of pediatric intensive-care patients are unknown due to the difficulty of measuring total energy expenditure in free-living conditions. We investigated energy expenditure and body composition in stable pediatric intensive-care patients receiving long-term ventilatory support. Total energy expenditure and total body water were measured in 10 such patients using the doubly-labeled water method. The patients had significantly lower energy expenditure than healthy children of the same age. Relative to length, fat-free mass deposition was significantly lower, and fat deposition was significantly greater, than in healthy subjects. In general, total energy requirements of these patients are significantly reduced as compared to healthy children, which can be attributed to their lower activity levels and their reduced muscle mass. Although they gain weight similar to healthy children, their weight gain is disproportionately higher in fat. However, one patient with myofibromatosis contradicted this general pattern.

Adipose Tissue↗

PubMedDate not supplied

A trade-off between early growth rate and fluctuating asymmetry in Brazilian boys.

BACKGROUND: Right-left discrepancies in normally symmetrical traits are assumed to result from inability of the individual to buffer environmental and genetic stresses. Fluctuating asymmetry (FA) may therefore signal the quality of an individual to potential mates, or to parents during early life. FA could signal the heritable ability to buffer stress-the 'good genes' hypothesis. Alternatively, FA could signal the degree of within-lifetime exposure to stress, in particular during specific sensitive periods of development--the 'good development' hypothesis. AIM: We tested the hypotheses that FA at 9 years of age is positively related to (a) fetal growth rate, (b) early infant growth rate, and (c) total post-natal growth rate. METHODS: FA, weight and height were measured in a sample of 172 boys aged 9 years from Pelotas, Brazil, who had previous measurements of weight and height at birth and 6 months. RESULTS: Fetal growth was not related to FA, however FA was positively related to total weight gain after birth (p < 0.05). This association could be broadly attributed to weight gain in the first 6 months of post-natal life (p = 0.075). Those currently obese had significantly greater FA than those non-obese (p < 0.05). CONCLUSIONS: Our results support the 'good development' hypothesis, and suggest that growth rate during an early post-natal critical window, previously linked to numerous health outcomes, also has long-term effects on FA.

Anthropometry↗