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Item Bone health and fracture risk factors in children living in New Zealand : a thesis presented in partial fulfilment of the requirement for the degree of Doctor of Philosophy in Nutritional Science at Massey University, Albany, New Zealand(Massey University, 2021) Delshad Siyahkaly, MaryamBackground: Fractures are common in childhood but are a neglected public health issue. A complex interplay of non-modifiable (e.g. genetics) and modifiable risk factors (e.g. obesity, physical activity, calcium intake, sugar-sweetened beverages (SSB), and vitamin D status) have been associated with childhood fractures. Early identification of risk factors during childhood could enable lifestyle changes to be instigated, thus enhancing bone mineralisation, preventing fractures, and improving adult bone health. Vitamin D is an essential nutrient for the absorption of calcium from the intestine, regulation of serum calcium, and bone health. An adequate 25(OH)D concentration is considered important for ensuring bone health during childhood since there is a relationship between vitamin D deficiency and insufficiency and skeletal health problems such as rickets, metabolic bone disease, and hypocalcaemia during childhood. Unfortunately, there is limited data available regarding the vitamin D status and risk factors for vitamin D deficiency in New Zealand children. Measuring paediatric bone mineral status can help us to find children who could be exposed to an increased risk of bone problems (e.g. osteopenia, osteoporosis) later in their life. Quantitative ultrasound (QUS) is a measuring method commonly employed in paediatric populations for assessing skeletal status. Childhood overweight and obesity are also associated with developing musculoskeletal problems, injuries, and fractures early in childhood. Recently, bioelectrical impedance analysis (BIA) has received much attention as a method for measuring body composition. However, the validity of these two devices needs to be investigated in a New Zealand paediatric population. Aims: The main aim of this study is to explore fracture history and related risk factors in children living in Auckland, New Zealand. The secondary aims are to determine the wintertime vitamin D status of children living in Auckland and its determinants and to validate the QUS and in-built algorithm of BIA measurements against dual-energy X-ray absorptiometry (DXA) in children. Methods: This was an observational, cross-sectional study in a sample of school-age children (aged 8 – 13 years old) living in Auckland (during August 2016 and 2017 – late winter in the southern hemisphere). Six local primary schools across Auckland were selected. We originally approached schools through a collaboration of primary school science teachers and asked for expressions of interest. We then endeavoured to recruit schools specifically to include a wide range of socio-demographic levels and ethnicities. All school children within the specified age group were invited to participate. Children were stratified by gender (2 groups), ethnicity (6 categories), and skin colour (4 groups), and logistic regression used to determine the contribution of risk factors for fracture and vitamin D deficiency. A sample of 10-15 per factor per group is the standard requirement for regression analysis, meaning that 480-720 participants would be required to investigate the above-mentioned factors. To validate the QUS and BIA, a sample of 128 children was calculated based on the G*Power program [version 3.1 software: medium effect size: 0.6; power: 95%; the level of significance: 5%]. Healthy children were recruited from primary schools. Children were excluded if they had 1) a history of any disease affecting vitamin D metabolism (e.g. cardiac, kidney or liver disease) or 2) a history of any long-term medication use (e.g. steroids) 3) had any surgical implants, metal screws or similar, or 4) had a cast. Children received an envelope containing a study information sheet, consent form, and some questionnaires (e.g. fracture history, siblings’ history of fractures, family osteoporosis history, physical activity (PA), ethnicity, skin colour, and sun exposure). A dairy and other calcium-containing foods food frequency questionnaire and SSB questionnaire were completed by the children with help from parents. Children who, together with their parents, gave written consent and returned the completed questionnaires, were measured at school. Tests included anthropometric (weight and height) and body composition (bioelectrical impedance analysis, InBody720, Seoul, Korea) measurements, and finger-prick blood spot to measure capillary 25-hydroxyvitamin D (25(OH)D) concentrations. Some children were invited to the Nutrition Research Facility at Massey University, Albany on one occasion to test the validity of the QUS and BIA measurements against a DXA scan. Total body less head (TBLH), bone mineral content (BMC), bone mineral density (BMD), and body composition (fat-free mass, fat mass, and body fat percentage (%BF)) were measured with DXA (QDR Discovery A, Hologic, USA); calcaneal BMD and stiffness index (SI) with QUS (Sahara QUS, Hologic, USA), and total mass and %BF on the InBody 230 (Biospace Ltd., Seoul, Korea). Relative validity was assessed using Pearson’s and Lin’s concordance correlation coefficients (CCC), and Bland-Altman plots. Results: A total of 647 children (354 girls) with the mean ± standard deviation (SD) age of 9.8 ± 0.7 years were recruited. New Zealand European (n = 252) (NZE) and South Asian (n = 68) children reported the lowest (20.2%) and highest (44.1%) fracture incidence, respectively. New Zealand European, compared to South Asian children, had higher 25(OH)D concentrations (74.6 ± 19.8 vs. 48.4 ± 19.3 nmol/L, P < 0.001), higher total calcium intake (764.0 ± 394.4 vs. 592.7 ± 266.3 mg/day, P < 0.018), and lower %BF (19.5 ± 6.6 vs. 23.4 ± 8.4, P < 0.003). The main determinants of fracture history for boys were high %BF, low 25(OH)D, low calcium intake, high SSB consumption, siblings’ fracture history, family osteoporosis history, and being South Asian; and for girls were high SSB consumption, siblings’ fracture history, and family osteoporosis history. Five hundred and seven children agreed to do the finger prick test. Mean ± SD 25(OH)D concentration were 64.0 ± 20.8 nmol/L, with 30.8% of the population presenting with 25(OH)D ≥ 75 nmol/L, 41.4% 50-75 nmol/L, and 27.8% < 50 nmol/L. Capillary 25(OH)D was significantly higher in NZE compared to all other ethnic groups (75.0 ± 20.1 nmol/L, P < 0.001). Children with dark/brown skin colour had lower 25(OH)D concentration compared to other categories of skin colour (51.7 ± 18.0 nmol/L, P < 0.001). Using multiple logistic regression analysis, determinants of 25(OH)D were %BF and ethnicity. In 124 healthy children, positive correlations between QUS SI and DXA (BMC and BMD) were observed (range = 0.30-0.45, P < 0.01). Results from Lin’s CCC test showed that almost perfect correlations between BIA and DXA fat-free mass (0.96), fat mass (0.92), and substantial correlation for %BF (0.75) (P < 0.05). Conclusion: Approximately one-quarter of our participants reported one or more fractures during their childhood. Our results showed that being of South Asian ethnicity was a significant risk factor for fracture in boys. Some children were at high risk of vitamin D deficiency during winter months, for whom vitamin D supplementation might be recommended. Good nutrition (especially good sources of calcium and reducing SSB intakes) should be recommended to children during growth and development to reduce their risk of fractures. Among 507 children, approximately one-third had 25(OH)D < 50 nmol/L. Determinants of a 25(OH)D < 50 nmol/L included %BF and ethnicity. Wintertime serum 25(OH)D was highly variable. There are some children at high-risk of 25(OH)D < 50 nmol/L for whom supplementation may be considered. The current study was the first to evaluate the validity of calcaneal QUS and BIA against DXA in a paediatric New Zealand population for measuring bone density and body composition, respectively. Although BIA results were not as accurate as DXA and DXA remains the gold standard method for clinical assessment, BIA can be an alternative method for investigating body composition among children in large cohort field studies. Calcaneal QUS and DXA are not interchangeable methods for measuring bone density in children similar to our study population.Item An investigation into the link between vitamin D status, erectile dysfunction and cardiovascular risk factors in ageing men in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Nutritional Science at Massey University, Palmerston North, New Zealand(Massey University, 2016) Quilter, Merrin LouiseBackground Cardiovascular disease (CVD) is the leading cause of death worldwide, particularly amongst ageing males. Prevention and/or early identification and effective intervention are essential in the fight against CVD. Erectile Dysfunction (ED) is a prevalent and multi-factorial condition that is now accepted to be an early marker of subclinical CVD: the common denominator is endothelial dysfunction. Both the enzymatic capability for bioactivation of Vitamin D and the vitamin D receptor (VDR) are expressed in endothelial cells and vitamin D may play a role in endothelial function. Vitamin D deficiency (serum 25-hydroxyvitamin D (25(OH)D) concentrations ˂50 nmol/L) is a worldwide pandemic and serum 25(OH)D levels ˂75 nmol/L may result in metabolic and vascular deterioration leading to endothelial dysfunction, ED and CVD. Assessment of erectile function can be used to identify otherwise asymptomatic men at high risk of developing clinical CVD, at a time when effective intervention may prevent, delay or reverse its progression. Vitamin D status may be associated with ED and CVD risk and could help improve erectile function and vascular health. Objectives The aim of this research was to investigate the postulated link between vitamin D status, ED, and CVD risk factors. The objectives were (1) to assess the prevalence of ED (using the 5-item International Index of Erectile Function (IIEF-5)) and its associated sociodemographic, lifestyle, and medical correlates in New Zealand (NZ) men aged 40-70 years; (2) to investigate the relationship between vitamin D status (serum 25(OH)D concentration), ED and other CVD risk factors in men aged 40-70 years living in the Manawatu region of NZ; and (3) to examine the impact of common VDR gene (VDR) polymorphisms on this relationship. Method Two thousand men aged 40-70 years were randomly selected from the NZ Electoral Roll and sent an anonymous postal survey designed to assess the prevalence of ED and its sociodemographic, lifestyle, and medical risk factors. Six hundred men aged 40-70 years living in the Manawatu region were randomly selected from the NZ Electoral Roll and invited to participate in an observational study designed to provide a comprehensive health profile of self-reported healthy men and investigate the relationship between vitamin D status, ED, and a range of CVD risk factors. Eligible participants (n=100) completed a comprehensive health assessment including a medical history, anthropometric and cardiovascular assessment, fasting blood sample, computer-based questionnaire, a submaximal fitness test and a handgrip iv strength test. Blood samples were assessed for four common VDR polymorphisms (rs11568820 (Cdx2), rs10735810 (FokI), rs1544410 (BsmI) and rs731236 (TaqI)) using polymerase chain reaction-high resolution amplicon melt (PCR-HRM) analysis. Results The survey showed 38.4% of respondents presented with ED (IIEF-5 ≤21). Older age, non-European ethnicity and current smoking were significant independent predictors of an increased risk of ED, while a high household income and regular vigorous physical activity (PA) were deemed protective. The observational study showed 30 men presented with ED and a further 37 men had <75 nmol/L 25(OH)D. There was a weak positive correlation between IIEF-5 scores and 25(OH)D levels (rs=0.238, p=0.017). Men with <75 nmol/L had lower IIEF-5 scores compared to men with ≥75 nmol/L 25(OH)D (22(7) vs. 24(3), p=0.001). Men with ED had lower 25(OH)D levels compared to men without ED (74.5(34) vs. 84.5(24), p=0.062). Every 1 nmol/L of 25(OH)D predicted a 2% decrease in the age-adjusted risk of ED (age-adjusted OR=0.98 [0.96-1.00], p=0.046). The PCR-HRM analysis showed that the Cdx2, FokI and BsmI polymorphisms were all significantly associated with an adverse cardiovascular risk profile. The Cdx2 G allele was associated with lower IIEF-5 scores compared to the A allele (23(4) vs. 24(2), p=0.008) and the GA and GG genotypes were predictors of an increased age-adjusted risk of ED (age-adjusted OR=18.78 [1.98-178.60], p=0.011 and 8.53 [1.00-72.73], p=0.050 respectively). However, Cdx2 was not found to modify the age-adjusted association between 25(OH)D levels and ED (multi-adjusted OR=0.97 [0.95-1.00], p=0.032). Conclusions These results suggest that over a third of NZ men aged 40-70 years suffer from ED and it is associated with sociodemographic, lifestyle and medical factors similar to CVD. Low serum 25(OH)D is associated with the presence and severity of ED in a self-reported healthy population. Common VDR polymorphisms are also associated with ED; however, they do not modify the association between serum 25(OH)D and ED. A randomised placebo-controlled human intervention trial is warranted to investigate whether improving vitamin D status in men with vitamin D deficiency and ED ameliorates symptoms and reduces the risk of CVD.Item Vitamin D status of preterm infants at 4 months past hospital discharge : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Science in Nutrition and Dietetics, Massey University, Albany, New Zealand(Massey University, 2013) Emmett, Briar KellyPreterm birth and survival rates are increasing in New Zealand and around the world. Preterm infants are subject to shorter gestational lengths and subsequently suffer from decreased nutrient accretion in utero. Vitamin D is one nutrient that is accrued in the final stages of gestation. At birth preterm infants rely on an exogenous source of this nutrient to achieve and maintain adequate stores. The vitamin D status of preterm infants after hospital discharge in New Zealand was previously unknown. The aim of this study was to investigate the serum 25-hydroxyvitamin D (25(OH)D) status of preterm infants at 4 months post hospital discharge, and describe the factors affecting these concentrations. An observational study of 49 preterm infants (<37 weeks gestation) at 4 months post hospital discharge was undertaken. A capillary blood sample was obtained from infants. Serum 25(OH)D was analysed using ADIVA Centaur Vitamin D Total immunoassay. Questionnaires were used to assess sun exposure behaviours and feeding and supplement use. In this sample of 49 preterm infants, 28.6% were classified as having insufficient vitamin D status (25(OH)D ≤50 nmol/L), of these 8.2% were further classified as having mild to moderate vitamin D deficiency (25(OH)D ≤25 nmol/L). The mean 25(OH)D concentration was 73.8 nmol/L, the range was 16 nmol/L – 314 nmol/L. Vitadol C supplementation had the most significant effect on infant 25(OH)D concentrations. All (n=14) exclusively breastfed infants who did not receive Vitadol C supplements were vitamin D insufficient or deficient on analysis. All infants who received Vitadol C or infant formula were vitamin D sufficient. Vitamin D deficiency is prevalent in exclusively breastfed preterm infants not receiving vitamin D supplements. Vitamin D supplementation should be considered for all preterm infants as part of New Zealand’s child health policy.