Participation in physical activity (PA) of at least moderate intensity may yield important health benefits for children. A popular behavioural tool used to promote increased PA is the pedometer. There is however limited evidence regarding pedometer-based strategies in children. This thesis reports on a series of anthropometric and accelerometer-measurement issue studies which inform the methods used to address the primary aim of this thesis- to determine the effectiveness of goal-setting, selfmonitoring and step-feedback pedometer-based interventions for increasing PA in 10- 11-year-old children. In addition, each study in their own right provides an original contribution to knowledge within their specific area of scholarship. The first objective of this thesis was therefore to determine diurnal variation of height and weight and the combined effect upon body mass index (BMI) weight status in children via a field based study. Next, the reliability of the Actiwatch 4 (AW4) accelerometer was tested in a mechanical laboratory experiment. Following this laboratory trial a second field based study examined the impact of placement site upon AW4 output, and the validity of a regression equation to predict hip-derived AW4 data from wrist-derived data. Finally, a brief intervention mapping approach was used to develop goal-setting, selfmonitoring and step-feedback pedometer-based interventions, the effectiveness of which was evaluated in a small scale controlled trial involving two primary schools. The main findings of this thesis were a) that diurnal variation in height (and in girls alone, weight) impact upon increased BMI and BMI percentile in afternoon versus morning measurements b) AW4 activity counts exhibit acceptable reliability statistics (comparable to other accelerometer models), which improve when raw activity counts are reduced into derived activity intensity variables c) wrist and hip derived AW4 data are not comparable, and the derived regression equation may not be suitable for group level prediction due to inaccurate individual level prediction and the large standard error of the estimate observed d) pilot testing pedometer wear and intervention materials may highlight practical pedometer issues (i.e. pedometer attachment, wearing compliance and acceptability of instruction sheets) that inform intervention implementation and e) pedometer-based goal-setting, self-monitoring and step-feedback interventions did not increase PA in 10-11-year-old children. However, individual-standardised goal setting may be more promising as this appeared to mitigate any decline in moderate-to-vigorous physical activity (MVPA) in moreactive children, and increased MVPA in less-active. To summarise, the findings of this thesis highlight important issues for physical activity scientists to consider when using BMI-determined weight status as a grouping variable and accelerometers as an outcome measure, when evaluating physical activity interventions in children. With regard to the primary aim of this thesis, future researchers should further examine the effectiveness of the individual-standardised against the group-standardised goal type in a longer-duration intervention and using a larger sample of children, which may permit sub-group analyses to be conducted. Of primary importance is future clarification on the effectiveness of goal setting, self-monitoring and step-feedback pedometer-based interventions per se for changing PA in children.

Most mutations in SCN1A-related epilepsies are novel and when an infant presents with febrile seizures (FS) it is uncertain if they will have simple FS, FS+ or develop a severe epilepsy such as Dravet Syndrome. The main aim of this work has been to translate specific genetic findings in SCN1A related epilepsies not only to the phenotype, but to examine the implications this has on treatment and quality of life in children and their families. Clinical and genetic data were collected from 273 individuals with SCN1A mutations identified in our laboratory between November 2005 and February 2010. I examined whether the mutation class, distribution or nature of amino acid substitution correlated with the epilepsy phenotype, using the Grantham Score (GS) as a measure of physicochemical difference between amino acids. From structured referral data I analysed a range of clinical characteristics including epilepsy phenotype, seizure precipitants, EEG data, imaging studies, mutation class and response to medication and determined predictors of developmental outcome. I developed novel ideas on how to characterise mutations in SCN1A related epilepsies, showing that phenotypes are not determined by chance, but are in part determined by defined physico-chemical changes affecting a specific location in the protein structure. I was able to demonstrate that these principles not only apply to the SCN1A gene but also to the wider voltage gated sodium channel family and related diseases. This study has been the largest to date to systematically examine the prognostic, clinical and demographic features of Dravet syndrome. The overall incidence of Dravet syndrome was found to be at least one in every 28,600 UK births. Clinical features predicting a worse developmental outcome included status epilepticus, interictal EEG abnormalities in the first year of life and a motor disorder. No significant effect was seen for seizure precipitants, MRI abnormalities or mutation class (truncating vs. missense). Sodium valproate, benzodiazepines and topiramate were reported the most helpful medications and aggravation of seizures was reported for carbamazepine and lamotrigine. Health related quality of life (HRQOL) has emerged as a widely accepted measure to evaluate how chronic disease impacts on an individual’s well-being and I examined in detail the comorbidities and predictors of health related quality of life in Dravet syndrome. HRQOL was evaluated with two epilepsy-specific instruments, the Impact of Pediatric Epilepsy Scale (IPES) and the Epilepsy & Learning Disabilities Quality of Life Questionnaire (ELDQOL), a generic HRQOL instrument the Pediatric Quality of Life Inventory (PedsQL) and a behavioural screening tool, the Strength and Difficulties Questionnaire (SDQ). 163 individuals with Dravet syndrome and their families participated in the questionnaire study. HRQOL was significantly lower for children with Dravet syndrome compared to normative data. One third of children had conduct problems and two thirds had hyperactive or inattentive behaviour. Regression analysis revealed that behavioural problems were the strongest predictors of poorer HRQOL. Identification of specific comorbidities will help us to better recognise and understand the needs of children and families with Dravet syndrome and facilitate a distinct multi-disciplinary approach to management. Genetic testing in the epilepsies has become an increasingly accessible clinical tool and this is the first study to assess the impact of SCN1A testing on patient management from both carer and physician perspectives. The vast majority of parents whose children tested positive for a mutation reported genetic testing helpful, leading to treatment changes resulting in fewer seizures, and improved access to therapies and respite care. Nearly half of the physicians reported that a positive test facilitated diagnosis earlier than with clinical and EEG data alone. In two thirds it prevented additional investigations and altered the treatment approach; it influenced medication choice in three quarters of cases and through medication change improved seizure control in forty percent. In addition to confirming a clinical diagnosis, a positive SCN1A test enabled early diagnosis, influenced treatment choice and facilitated improvements in clinical management, especially in the very young. Finally I hope that this work will contribute to a better understanding of the causes of SCN1A related epilepsies. Furthermore I hope that it will provide evidence to aid earlier diagnosis and treatment of children with severe infantile epilepsies and that it will offer more information for genetic counselling. These improvements in epilepsy care and seizure control could help prevent or reduce the disability associated with SCN1A related epilepsies such as learning and behaviour problems and would improve the quality of life for children and families.

Background – Physical activity (PA) has been shown to have numerous physical (e.g., reduced risk of cardiovascular disease, type-2 diabetes and obesity) and psychological (e.g., improved mental well-being, and reduction in levels of stress and depression) benefits for childhood health. Despite the known benefits, childhood PA levels are low in Scotland, where less than 20% of children achieve the recommended daily guidelines. Evidence suggests that time spent outside is positively associated with achieving higher PA levels. Understanding what might encourage children to spend time outside in their neighbourhood could inform the development of interventions aimed at encouraging children to be more active. Children from different socio-spatial neighbourhoods may perceive and utilise their neighbourhood differently, influencing how they spend their free time. This PhD thesis examines how children from diverse settings perceive their neighbourhood in relation to their outdoor activity behaviours. Methods – This thesis takes a qualitative, multi-methodological approach, towards understanding 10-11 year old children’s perceptions of their environment in relation to their time spent outside through the lens of Gibson’s theory of affordances. A pilot study (n=15, 5 boys, 10 girls) was conducted to test the feasibility of the methods. For the main study, the children (n=25, 12 boys, 13 girls) were from different levels of area deprivation and from varying levels of urbanicity. Data collection methods included photo voice, drawings, focus groups or interviews. The participants were asked to document features within their environment (via photographs and drawings) that they felt influenced their time outside. They were then asked to participate in either a focus group or a one-to-one interview. The data collection process took place between May and September 2015. Findings – Children’s perceptions of their neighbourhood environments are complex, and numerous differences were found to be dependent on area of residence. Children from rural areas appeared to be influenced more by physical affordances whereas children living in urban settings were influenced more by social affordances, specifically their friends. Children living in more deprived neighbourhoods spoke of needing more PA opportunities in their neighbourhood compared to children living in more affluent neighbourhoods, suggesting that inequalities may still exist between higher and lower area deprivation. Many of the children considered current play equipment too boring, and lacked challenge or risk. The children desired equipment that better suited their perceived capabilities. This thesis found that children were more likely to spend time outside for psychological reasons, such as relaxation. Conclusion – Through the use of novel methodology in this subject area, this thesis adds an original contribution to the literature by exploring children’s environmental perceptions in relation to PA, and by looking at how setting might influence these perceptions. This thesis found that children perceive their environment differently dependent on the context of their lives, suggesting that initiatives to increase childhood PA could differ depending on residential setting. Additionally, policy may emphasize the psychological benefits to children as opposed to the physical benefits. Highlighting benefits such as relaxation, happiness and excitement may be more conducive to increasing PA among this age group than focusing on benefits such as weight management and cardiovascular health.

NHS reforms have sought to ensure that children and young people who are ill receive timely, high quality and effective care as close to home as possible (DH, 2004). This study examined the experience and impact of introducing new, ‘closer to home’ community-based paediatric outpatient clinics from the perspectives of NHS service-users and providers. Twenty-seven interviews conducted with parents and patients (aged 8-16), were analysed using a descriptive phenomenological approach. Thirty-seven interviews conducted with healthcare professionals, were analysed using a thematic framework method. Findings reveal that paediatric outpatient ‘care close to home’ is experienced in ways that go beyond concerns about location and proximity. For families it means care that ‘fits into their lives’ spatially, temporally and emotionally; facilitating a sense of ‘at-homeness’ within the self and within the place, through the creation of a warm and welcoming environment, and by providing timely consultations which attend to aspects of the families’ lifeworld. For service-providers, place and professional identity were closely related, with implicit assumptions made about where high quality of care and clinical expertise were located. Place, time and human relations were thus shown to be meaningful constituents of the experience of paediatric outpatient care. These previously ‘taken-for-granted’ nuances of healthcare delivery have implications for the design and implementation of effective ‘closer to home’ services.

Children are uniquely placed in a context where external influences are likely to determine their food consumption. Evidence regarding the immediate food environment’s influence on dietary quality and/or weight status in children is limited. This thesis uses data from the West Midlands ActiVe lifestyle and healthy Eating in School children (WAVES) study to explore patterns of dietary intake in children aged 5-9 years (n=1467), some of the determinants of children's dietary consumption and their associations with child weight status. Findings suggest that children’s dietary consumption needs to be more healthful, and aspects of children's school and home life may have the potential to influence dietary quality and weight status. Specifically, a healthy home food environment was associated with increased fruit and vegetable intake and a lower weight status. Certain parental feeding practices, such as using food as a reward or to regulate emotion, were also associated with increased energy intake from free sugar and weight status. In conclusion, various environmental and behavioural factors are associated with children’s dietary intake and as such, coordinated efforts in a variety of settings are required to affect the ‘what’, ‘how’ and ‘in what context’ of children’s dietary consumption and consequently childhood obesity prevalence.

The Cognitive Abilities Profile (CAP) (Deutsch and Mohammed, 2010) is a collaborative tool for psychologists and teachers. The CAP is based on principles of Dynamic Assessment (DA) and uses a consultative model for rating pupils' cognitive abilities in various cognitive domains and for planning interventions to facilitate pupils' progress accordingly. The CAP was developed in response to a perceived need for educational psychologists (EPs) to have access to alternative assessments to standardised psychological tests, particularly in the case of learning disadvantaged and ethnic minority pupils. Using DA as one possible approach creates a need for EPs to have access to training and to receive support with the implementation of DA-based intervention methods within local services. However, surveys of EP use of DA indicate limitations in training, inadequate support and difficulties in wider application of DA. In the present work, a quantitative methodology has been used to examine the validity and reliability of the CAP in overcoming the above-noted difficulties in the implementation of DA by EPs. The methodology involved the collection and analysis of data from three groups of EPs, two of which conducted consultations with teachers using the CAP and the third group of EPs used its own choice of consultation methodology and functioned as a control group. The findings of the present work provide evidence of good construct validity of the CAP cognitive domains, adequate inter-rater reliability between CAP users and evidence of advantage for pupils in some areas of functioning between pre- and post-use of the CAP, as validated by independent standardised tests. Analysis of perceptions of EPs of the utility of the CAP, based on the results of feedback questionnaires, addresses issues of user friendliness of the CAP. CAP users agreed on the need for initial training for psychologists and support for practitioners. The findings have implications for adoption of a novel approach in EP and teacher related work.

The effects of androgens reach far and wide and can be physiological as well as pathological. They are not limited to males and involve almost every system in the human body. Their influence on reproductive development and behaviours is well studied, but more recently, attention has turned to the wider reaching consequences of androgen exposure. Disorders of sex development (DSD) are rare conditions in which individuals may be deficient in, or resistant to, the effects of androgens. The long-term health and quality of life for these individuals is not well reported, but where there are reports, there are descriptions of increased depressive like behaviours, anxiety and poor social functioning. Lack of androgens has been linked to poorer neurocognitive outcomes in some studies and there is a concern that more aggressive hormone replacement should be considered in early life for those individuals lacking in androgens. These disorders can be difficult to study for many reasons. Firstly, they are rare conditions. Secondly, adults with DSD do not tend to visit hospital regularly and can therefore be challenging to engage in research. Thirdly, studying the effects of early life exposure to steroid hormones and relating these to later life behaviours is incredibly complex. Animal models have been used for many years to study the hormonal environment. For my first study, I used a model of rodent neonatal androgen blockade by treating pups with the anti-androgen flutamide for the first five days of life. The animals were studied again in adolescence (6 weeks of age) and early adulthood (10 weeks of age). There were no significant differences found in testosterone, dihydrotestosterone and androstenedione levels in either age group, demonstrating that the androgen blockade was transient. The anogenital index (AGI) was significantly shorter in the treated animals when compared to controls at 6 weeks of age and 10 weeks of age. Phallus length was significantly shorter in treated males when compared to the healthy males at 6 weeks of age and at 10 weeks of age. Phallus weight was significantly lower in the treated animals at 10 weeks of age when compared to the healthy animals. This work demonstrated that my rodent model of neonatal androgen blockade was an effective one. My next study used the same rodent model and aimed to link the perinatal hormonal environment with in vivo brain chemistry using a painless, non-invasive technique known as Magnetic Resonance Spectroscopy. Using a mixed effects model, I analysed the effects of sex, gender, treatment with flutamide and age on the metabolite pattern of the rodent brain. Ɣ-aminobutyric acid (GABA), glucose, glutamine, glutamate, phosphocholine and myo-inositol all changed over time. The combined peaks of glutamate and glutamine also demonstrated a significant change over time. GABA, glutamate, phosphocholine and myo-inositol showed significant sex differences as did the combined peaks of glycerophosphocholine and phosphocholine, N-acetylaspartate (NAA) and N-acetylaspartylglutamate (NAAG) and glutamate and glutamine. Aspartate, GABA and myo-inositol were all significantly changed by treatment of the animals with flutamide and GABA and myo-inositol levels in treated males were similar to control females at both 6 and 10 weeks. My final study using the rodent model of androgen blockade looked at the histological changes in the brain. Brains were sectioned and stained for neuronal cell counts and microglial cell counts, and PCR for the Androgen Receptor (AR) was performed. I demonstrated significant, sexually dimorphic changes in neuronal cell counts, microglial cell counts and androgen receptor expression in two clearly defined areas in the rodent brain. In summary, my rodent work demonstrated a link between the neonatal hormonal environment and the sexually dimorphic chemistry and histology of the in vivo brain, and supports the hypothesis that the microglial cell plays a critical role in brain masculinisation. To include a translational aspect to this thesis I extended my work to a population of undermasculinised boys, who were attending hospital for an hCG stimulation test as part of their investigations for 46 XY DSD. The hCG stimulation test is a valuable method for assessing androgen production but there is a need to explore its utility in assessing androgen responsiveness and long-term prognosis. I aimed to assess the effects of the hCG test on the in vivo brain chemistry using MRS, and the peripheral transcriptome using microarray. I reliably demonstrated metabolites in the brains of healthy male infants, healthy female infants and affected male infants. Healthy male infants had significantly lower levels of N-acetylaspartate than affected males in the hypothalamus and lower levels of the phosphocholines in the frontal cortex. In my transcriptomic study of DSD patients, I demonstrated the existence of an androgen responsive group of small RNAs that are measurable in peripheral mononuclear blood cells, and that change over the short duration of an hCG stimulation test, raising the prospect of combining the biochemical assessment of testosterone production with an objective molecular assessment of androgen sufficiency. In summary, in this thesis I have successfully linked the early hormonal environment with later life in vivo brain chemistry, confirmed by histological studies. I have also identified a novel marker, which could potentially be used as an assessment of androgen sufficiency in the future.

Hypoglycaemia is an unavoidable consequence of treatment of Type 1 Diabetes Mellitus (T1DM). Symptoms are often embarrassing and distressing and can lead to the development of fear of hypoglycaemia (FoH). This fear can have a negative impact on diabetes management and can lead to further medical complications. 210 children and young people (CYP), aged 3-17 years and 190 parents from diabetes paediatric clinics across the West Midlands, UK, completed questionnaires exploring the prevalence of hypoglycaemia, FoH and links to hypoglycaemia awareness, self-care, quality of life and anxiety. Demographic information and HbA1c data were also collected. Results indicated that hypoglycaemia and severe hypoglycaemia (SH) are a problem for CYP in the UK. Hypoglycaemia Fear Survey (HFS) scores were higher in parents than in CYP (Total HFS 37.1±14.9 vs. 50.2±17.8 vs. 45.2±18.0, CYP vs. mother vs. father, respectively, p < 0.01). Adolescents with prior experience of severe hypoglycaemia (SH) had higher HFS scores compared to those without (t=-3.61, p < 0.001). Trait anxiety and SH explained 23% of the variance in HFS scores in adolescents. Trait anxiety explained 37% of the variance in HFS scores in under 11 year olds, 18% in mothers of under 11 year olds, 6% in mothers of adolescent and 10% in fathers of adolescents. There was no correlation between HFS and HbA1c. Qualitative analyses identified ‘Burden’ as an overarching theme from CYP and parent interviews. ‘Negative emotions’ and ‘Living with diabetes’ emerged as the key themes of analysis. This research study adds to existing findings on the prevalence of hypoglycaemia, severe hypoglycaemia, FoH and possible related factors, by focusing on the paediatric population and their parents, in the UK, for which there is limited research. Qualitative analyses also provided novel reports of the experience of T1DM for CYP and their mothers. Implications of this research could lead to the development of an FoH and anxiety managementprogramme for CYP and their parents. The findings of this study also help to raise awareness of this very real and current issue in diabetes management.

Introduction: Despite the method existing for centuries, uses of crowdsourcing have been rising rapidly since the term was coined a decade ago. Crowdsourcing refers to ‘outsourcing’ a problem or task to a large group of people (i.e., a crowd) rapidly and cheaply. Researchers debate over definitions of crowdsourcing, and it is often conflated with mHealth, web 2.0, or data mining. Due to the inexpensive and rapid nature of crowdsourcing, it may be particularly amenable to health research and practice, especially in a global health context, where health systems, human resources, and finances are often scarce. Indeed, one of the dominant methods of health research prioritization uses crowdsourcing, and in particular, wisdom of the crowds. This method, called the Child Health and Nutrition Research Initiative (CHNRI) method, employs researchers to generate and rank research options which are scored against pre-set criteria. Their scores are combined with weights for each criterion, set by a larger, diverse group of stakeholders, to create a ranked list of research options. Unfortunately, due to difficulties in defining and assembling a group of stakeholders that would be appropriate to each exercise, 75% of CHNRI exercises to-date did not involve stakeholders, and therefore presented unweighted ranks. Methods: First, a crowdsourcing was defined through a literature review. Benefits and challenges of crowdsourcing were explored, in addition to ethical issues with crowdsourcing. A second literature review was conducted to explore ways in which crowdsourcing has been already used in health and global health. As crowdsourcing could be a potential solution to data scarcity or act as a platform for intervention in global health settings, but its potential has never been systematically assessed, a CHNRI exercise was conducted to explore potential uses of crowdsourcing in global health and conflict. Experts from both global health and crowdsourcing participated in generation and scoring ideas. This CHNRI exercise was conducted in-line with previously described steps of the CHNRI method for setting health research priorities. As three quarters of CHNRI exercises have not utilized a larger reference group (LRG) of stakeholders, and the public was cited as the most difficult stakeholder group to involve, we conducted a survey using Amazon Mechanical Turk, an online crowdsourcing platform, that involved an international group of predominantly laypersons who, in essence, formed a public stakeholder group, scoring the most common CHNRI criteria using a 5-point Likert scale. The resulting means were converted to weights that can be used in upcoming exercises. Differences in geographic location, and whether the respondents were health stakeholders were assessed through the Fisher exact test and Wilcoxon rank-sum test, respectively. The influence of other demographic characteristics was explored through random-intercept modelling and logistic regression. Finally, an example of a national-level CHNRI exercise, which is the largest CHNRI conducted to-date, exploring research priorities in child health in India is described. Results: A comprehensive definition of crowdsourcing is given, along with its benefits, challenges, and ethical considerations for using crowdsourcing, based on a literature review. An overview of uses of crowdsourcing in health are discussed, and potential challenges and techniques for improving accuracy, such as introducing thresholds, qualifiers, introducing modular tasks and gamification. Crowdsourcing was frequently used as a diagnostics or surveillance tool. The CHNRI method was not identified in the second literature review. In re-weighting the CHNRI criteria using a public stakeholder group, we identified differences in relative importance of the criteria driven by geographic location and health status. When using random-intercept modelling to control for geographic location, we found differences due to health status in many criteria (n = 11), followed by gender (n = 10), ethnicity (n = 9), and religion (n = 8). We used the CHNRI method to explore potential uses of crowdsourcing in global health, and found that the majority of ideas were problem solving or data generation in nature. The top-ranked idea was to use crowdsourcing to generate more timely reports of future epidemics (such as in the case of Ebola), and other ideas relating to using crowdsourcing for the surveillance or control of communicable disease scored highly. Many ideas were related to the United Nations’ Sustainable Development Goals (SDGs). Finally, a national-level exercise to set research priorities in child health in India identified differential priorities for three regions (Empowered Action Group and North Eastern States, Northern States and Union Territories, and the Southern and Western States). The results will be very useful in developing targeted programmes for each region, enabling India to make progress towards SDG 3.2. Conclusion: Crowdsourcing has grown exponentially in the past decade. Integrating gamification, machine learning, simplifying tasks and introducing thresholds or trustworthiness scores increases accuracy of results. This research provides recommendations for improvements in the CHNRI method itself, and for crowdsourcing, generally. Crowdsourcing is a rapid, inexpensive tool for research, and thus, is a promising data collection method or intervention for health and global health.

The World Health Organization (WHO) recommends exclusive breast-feeding until 6 months of age, where exclusive breast-feeding is defined as giving human breast milk only with no other foods or fluids. This recommendation has since been adopted by many countries. A systematic review of studies in exclusively breast-fed infants by Reilly and colleagues found a mean milk intake at 6 months of age that seemed too low to cover infant energy requirements. However, the evidence was relatively scarce, only from cross-sectional studies and based on the method of test-weighing, which has been criticised for under-estimating milk intake. Furthermore, longitudinal studies indicated no marked increase in milk intake over time, but these studies did not include measurements at 6 months of age. Reilly and Wells proposed the hypothesis that for exclusive breast-feeding to adequately cover infant energy requirements to 6 months of age, either 1) infants had to be unusually small, or 2) breast milk energy content had to be unusually high, or 3) milk intake had to be unusually high. The Reilly-Wells hypothesis was backed up by evidence of a world-wide low prevalence of exclusive breast-feeding to 6 months, and by studies consistently reporting a maternally perceived insufficient milk supply as a major reason for mothers to cease exclusive breast-feeding and introduce either formula supplementation or complementary foods. Based on the Reilly-Wells hypothesis, the research question for the First-Feed study was: To explore how exclusive breast-feeding to 6 months of age is achievable – mainly from an energy balance point of view. The First-Feed study tested the hypothesis that successful exclusive breast-feeding to 6 months of age would include 1) infants that were small and/or growing slowly, 2) milk intakes and/or milk energy content that were higher than literature values and increasing over time, 3) infant energy requirements that were lower than reference values, and/or 4) infant feeding practices that were strained by very frequent and/or very time consuming breast-feeds. The study was designed as the first longitudinal observational study to use an isotopic method to measure milk intake and energy balance in exclusively breast-fed infants to 6 months of age, and it evaluated parts of the methodology employed in the study, in order to appreciate the results in light of the methodological strengths and limitations. The First-Feed study found that infants were overall of normal size and growing well relative to WHO Child Growth Standards. Metabolisable milk intakes were significantly higher than the values obtained by Reilly and colleagues at both 3½ and 6 months of age, and increased significantly over time. Infant energy requirements, determined as metabolisable energy intake, was significantly higher than references for mean energy requirements at 3½ months of age, while it was appropriate at 6 months of age. Breast-feeding practices showed no change over time in feeding frequency, but a significant decrease in time spent on breast-feeds. The First-Feed study had several limitations. Firstly, due to the inclusion criteria of exclusive breast-feeding, the participants were characterised as an affluent and well-supported sample of mother-infant pairs, who were highly motivated to breast-feed. Therefore, the generalisability of the present study to other populations should be accepted with caution. Secondly, the anthropometric measurements were prone to imprecision, as is often the case in field studies. Thirdly, the imprecision of the dose-to-infant procedure for administration of doubly-labelled water considerably reduced the precision of the doubly-labelled water method. This, in addition to the biological variation, increased the variation in some outcome variables. However, the First-Feed study is unique as it is the first to use a more objective method to measure milk intake in a longitudinal design, and on a sample of infants with a very high success rate of exclusive breast-feeding to 6 months of age. The WHO changed the recommendation on exclusive breast-feeding from 4 – 6 months to 6 months (exactly) in 2001. Since then, many resources have been invested in breast-feeding promotion, but rates of initiation, duration and exclusivity is only slowly improving. The present study supports that exclusive breast-feeding can adequately cover infant energy requirements to 6 months of age - even without undue strain on breast-feeding practices and even in mothers where initial breast-feeding problems were very common. However, the present study found a wide variation in both infant size, milk intake and energy requirements. It therefore begs the question if a recommendation based on one age-point (6 months exactly) is appropriate given the vast biological variation in variables that are important for the adequacy of exclusive breast-feeding, or if the recommendation should be adapted to include developmental milestones (e.g. oral motor skills) indicative of readiness for complementary foods.