Acute CO2 tolerance in fishes is associated with air breathing but not the Root effect, red cell ßNHE, or habitat.

High CO2 (hypercapnia) can impose significant physiological challenges associated with acid-base regulation in fishes, impairing whole animal performance and survival. Unlike other environmental conditions such as temperature and O2, the acute CO2 tolerance thresholds of fishes are not understood. While some fish species are highly tolerant, the extent of acute CO2 tolerance and the associated physiological and ecological traits remain largely unknown. To investigate this, we used a recently developed ramping assay, termed the Carbon Dioxide maximum (CDmax), that increases CO2 exposure until loss of equilibrium (LOE) is observed. We investigated if there was a relationship between CO2 tolerance and the Root effect, ß-adrenergic sodium proton exchanger (ßNHE), air-breathing, and fish habitat in 17 species. We hypothesized that CO2 tolerance would be higher in fishes that lack both a Root effect and ßNHE, breathe air, and reside in tropical habitats. Our results showed that CDmax ranged from 2.7 to 26.7 kPa, while LOE was never reached in four species at the maximum PCO2 we could measure (26.7 kPa); CO2 tolerance was only associated with air-breathing, but not the presence of a Root effect or a red blood cell (RBC) ßNHE, or fish habitat. This study demonstrates that the diverse group of fishes investigated here are incredibly tolerant of CO2 and that although this tolerance is associated with air-breathing, further investigations are required to understand the basis for CO2 tolerance.

Preferential intracellular pH regulation is a common trait amongst fishes exposed to high environmental CO2.

Acute (<96 h) exposure to elevated environmental CO2 (hypercarbia) induces a pH disturbance in fishes that is often compensated by concurrent recovery of intracellular and extracellular pH (pHi and pHe, respectively; coupled pH regulation). However, coupled pH regulation may be limited at CO2 partial pressure (PCO2 ) tensions far below levels that some fishes naturally encounter. Previously, four hypercarbia-tolerant fishes had been shown to completely and rapidly regulate heart, brain, liver and white muscle pHi during acute exposure to >4 kPa PCO2  (preferential pHi regulation) before pHe compensation was observed. Here, we test the hypothesis that preferential pHi regulation is a widespread strategy of acid-base regulation among fish by measuring pHi regulation in 10 different fish species that are broadly phylogenetically separated, spanning six orders, eight families and 10 genera. Contrary to previous views, we show that preferential pHi regulation is the most common strategy for acid-base regulation within these fishes during exposure to severe acute hypercarbia and that this strategy is associated with increased hypercarbia tolerance. This suggests that preferential pHi regulation may confer tolerance to the respiratory acidosis associated with hypercarbia, and we propose that it is an exaptation that facilitated key evolutionary transitions in vertebrate evolution, such as the evolution of air breathing.

Genetic predisposition to adiposity is associated with increased objectively assessed sedentary time in young children.

Increased sedentariness has been linked to the growing prevalence of obesity in children, but some longitudinal studies suggest that sedentariness may be a consequence rather than a cause of increased adiposity. We used Mendelian randomization to examine the causal relations between body mass index (BMI) and objectively assessed sedentary time and physical activity in 3-8 year-old children from one Finnish and two Danish cohorts [NTOTAL=679]. A genetic risk score (GRS) comprised of 15 independent genetic variants associated with childhood BMI was used as the instrumental variable to test causal effects of BMI on sedentary time, total physical activity, and moderate-to-vigorous physical activity (MVPA). In fixed effects meta-analyses, the GRS was associated with 0.05 SD/allele increase in sedentary time (P=0.019), but there was no significant association with total physical activity (beta=0.011 SD/allele, P=0.58) or MVPA (beta=0.001 SD/allele, P=0.96), adjusting for age, sex, monitor wear-time and first three genome-wide principal components. In two-stage least squares regression analyses, each genetically instrumented one unit increase in BMI z-score increased sedentary time by 0.47 SD (P=0.072). Childhood BMI may have a causal influence on sedentary time but not on total physical activity or MVPA in young children. Our results provide important insights into the regulation of movement behaviour in childhood.

Associations between adiposity, hormones, and gains in height, whole-body height-adjusted bone size, and size-adjusted bone mineral content in 8- to 11-year-old children.

UNLABELLED: We examined fat-independent associations of hormones with height and whole-body bone size and mineral content in 633 school children. IGF-1 and osteocalcin predict growth in height, while fat, osteocalcin, and in girls also, IGF-1 predict growth in bone size. Leptin and ghrelin are inversely associated with bone size in girls. INTRODUCTION: Obesity causes larger bone size and bone mass, but the role of hormones in this up-regulation of bone in obesity is not well elucidated. We examined longitudinal associations between baseline body fat mass (FM), and fat-independent fasting levels of ghrelin, adiponectin, leptin, insulin, insulin-like growth factor-I (IGF-1), osteocalcin, and intact parathyroid hormone, and subsequent changes in height and in whole-body height-adjusted bone area "BAheight" and size-adjusted bone mineral content "BMCsize" in 8- to 11-year-olds. METHODS: Analyses were carried out separately for boys (n = 325) and girls (n = 308) including data from baseline, 3 and 6 months from OPUS School Meal Study. RESULTS: In both sexes: gain in BAheight was positively associated with baseline FM (≥2.05 cm(2)/kg, both p ≤ 0.003). Furthermore, gain in height was positively associated with baseline IGF-1 (≥0.02 cm/ng/ml, p = 0.001) and osteocalcin (≥0.13 cm/ng/ml, p ≤ 0.009); and gain in BAheight was positively associated with baseline osteocalcin (≥0.35 cm(2)/ng/ml, p ≤ 0.019). In girls only, gain in BAheight was also positively associated with baseline IGF-1 (0.06 cm(2)/ng/ml, p = 0.017) and inversely associated with both baseline ghrelin (-0.01 cm(2)/pg/ml, p = 0.001) and leptin (-1.21 cm(2)/µg/ml, p = 0.005). In boys, gain in BMCsize was positively associated with osteocalcin (0.18 g/ng/ml, p = 0.030). CONCLUSIONS: This large longitudinal study suggests that in 8- to 11-year-old children, IGF-1 and osteocalcin predict growth in height, while FM, osteocalcin, and in girls also, IGF-1 predict growth in BAheight. Fat-independent inverse associations of leptin and ghrelin with BAheight in girls' are contrary to proposed growth-stimulating effects of leptin. Osteocalcin in boys predicts gain in BMCsize.

Maternal fish oil supplementation during lactation is associated with reduced height at 13 years of age and higher blood pressure in boys only.

Dietary long-chain n-3 PUFA (n-3 LCPUFA) in infancy may have long-term effects on lifestyle disease risk. The present follow-up study investigated whether maternal fish oil (FO) supplementation during lactation affected growth and blood pressure in adolescents and whether the effects differed between boys and girls. Mother-infant pairs (n 103) completed a randomised controlled trial with FO (1·5 g/d n-3 LCPUFA) or olive oil (OO) supplements during the first 4 months of lactation; forty-seven mother-infant pairs with high fish intake were followed-up for 4 months as the reference group. We also followed-up 100 children with assessment of growth, blood pressure, diet by FFQ and physical activity by 7-d accelerometry at 13·5 (sd 0·4) years of age. Dried whole-blood fatty acid composition was analysed in a subgroup (n 49). At 13 years of age, whole-blood n-3 LCPUFA, diet, physical activity and body composition did not differ between the three groups. The children from the FO group were 3·4 (95 % CI 0·2, 6·6) cm shorter (P=0·035) than those from the OO group, and tended to have less advanced puberty (P=0·068), which explained the difference in height. There was a sex-specific effect on diastolic blood pressure (P sex×group=0·020), which was driven by a 3·9 (95 % CI 0·2, 7·5) mmHg higher diastolic blood pressure in the FO compared with the OO group among boys only (P=0·041). Our results indicate that early n-3 LCPUFA intake may reduce height in early adolescence due to a delay in pubertal maturation and increase blood pressure specifically in boys, thereby tending to counteract existing sex differences.

Differences in the effects of school meals on children's cognitive performance according to gender, household education and baseline reading skills.

BACKGROUND/OBJECTIVES: We previously found that the OPUS School Meal Study improved reading and increased errors related to inattention and impulsivity. This study explored whether the cognitive effects differed according to gender, household education and reading proficiency at baseline. SUBJECTS/METHODS: This is a cluster-randomised cross-over trial comparing Nordic school meals with packed lunch from home (control) for 3 months each among 834 children aged 8 to 11 years. At baseline and at the end of each dietary period, we assessed children's performance in reading, mathematics and the d2-test of attention. Interactions were evaluated using mixed models. Analyses included 739 children. RESULTS: At baseline, boys and children from households without academic education were poorer readers and had a higher d2-error%. Effects on dietary intake were similar in subgroups. However, the effect of the intervention on test outcomes was stronger in boys, in children from households with academic education and in children with normal/good baseline reading proficiency. Overall, this resulted in increased socioeconomic inequality in reading performance and reduced inequality in impulsivity. Contrary to this, the gender difference decreased in reading and increased in impulsivity. Finally, the gap between poor and normal/good readers was increased in reading and decreased for d2-error%. CONCLUSIONS: The effects of healthy school meals on reading, impulsivity and inattention were modified by gender, household education and baseline reading proficiency. The differential effects might be related to environmental aspects of the intervention and deserves to be investigated further in future school meal trials.

Physical activity, sleep duration and metabolic health in children fluctuate with the lunar cycle: science behind the myth.

Behaviours of several animal species have been linked to lunar periodicity. Evidence for such links in humans is weak; however, recently, shorter sleep duration was reported around full moon in two small samples of adults. As restrictions in sleep duration have been shown to adversely affect glucose regulation and physical activity to improve glucose regulation, one could speculate that cardiometabolic risk factors might also be affected by the lunar phase. We retrospectively examined 795 Danish children, aged 8-11 years, with more than 13,000 24-h accelerometer recordings of activity and sleep as well as 2000 measurements of different cardiometabolic risk factors, including insulin sensitivity, appetite hormones and blood pressure, during nine lunar phases. During the period around full moon, children were 5.0 and 3.2 min per day less active, slept 2.4 and 4.1 min per night longer, had 0.03 and 0.05 higher homeostatic model assessment of insulin resistance and 0.6 and 0.8 mmHg higher mean arterial blood pressure compared with days around half moon and new moon, respectively (all P ≤ 0.02). Furthermore, ghrelin was lower and leptin was higher during the period around full moon compared with days around half moon (both P < 0.001). The results suggest that physical activity rather than sleep is responsible for the metabolic alterations observed around full moon. However, we have no understanding of potential mechanisms that may mediate a potential true link between childhood behaviour and the lunar cycle or confounders that may explain this, apparently leading to fluctuation in a number of cardiometabolic risk markers conjointly with lunar phases.

Do healthy school meals affect illness, allergies and school attendance in 8- to 11-year-old children? A cluster-randomised controlled study.

BACKGROUND/OBJECTIVES: A nutritionally adequate diet in childhood is important for health and resistance of allergies and infections. This study explored the effects of school meals rich in fish, vegetables and fibre on school attendance, asthma, allergies and illness in 797 Danish 8- to 11-year-old children. No comparable studies conducted in high-income settings have been identified. SUBJECTS/METHODS: The OPUS School Meal Study was a cluster-randomised cross-over trial. Children from third and fourth grades at nine Danish schools received school meals or usual packed lunch (control) for two 3-month periods. Occurrence and duration of illnesses, asthma and allergies during the last 14 days were recorded by parental questionnaires at baseline and after each 3-month period. Self-reported well-being was assessed by visual analogue scales. RESULTS: The school meals did not affect school attendance, parent-reported occurrence or duration of asthma and allergies or self-reported well-being. The most common symptoms of illness were stomach pain (24%), headache (28%) and cold (24%). A slightly higher number of children experienced headaches in the school meal (27%) compared with the control period (22%) (P=0.02). However, subgroup analyses showed that this effect was only seen in children eating school meals in the classroom (P=0.007), and not in common dining areas (P=0.2). No effect was found on other symptoms of illness. CONCLUSIONS: Provision of nutritionally balanced school meals did not affect school attendance, asthma, allergies, illness or well-being in 8- to 11-year-old children. The slight increase in occurrence of headaches seems to be related to the physical eating environment.

Back-transformation of treatment differences--an approximate method.

BACKGROUND/OBJECTIVES: Transformation of outcomes is frequently used in the analysis of studies in clinical nutrition. However, back-transformation of estimated treatment means and differences is complicated by the nonlinear nature of the transformations. It is not straightforward to obtain an estimated treatment difference that can be interpreted without any reference to the additional predictors included in the statistical model; and moreover, standard errors are not easily available. The aim of this work was to provide a generally applicable, yet operational procedure for obtaining back-transformed estimated differences, and corresponding standard errors and 95% confidence intervals. SUBJECTS/METHODS: Based on data from two randomized controlled studies and an exemplary data set that had all previously been published, we evaluated our approximate procedure by comparing results for different approaches for showing back-transformed estimated treatment differences. RESULTS: Estimated differences obtained on logarithm, square root and reciprocal square root-transformed scales were back-transformed into estimated differences on the original scales, and these estimates were in good agreement with the results reported by the original studies. CONCLUSIONS: The proposed approximate procedure provides a flexible approach for obtaining quite accurate back-transformed estimated differences in terms of medians and for deriving the corresponding standard errors.