Effect of vitamin D supplementation on bone status, glucose homeostasis and immune function in children with vitamin D deficiency

Background: Between 1961-1971 vitamin D deficiency was recognized as a public health issue in the UK, because of the lack of effective sunlight and the population mix [1, 2]. In recent years, health care professionals have cited evidence suggesting a re-emergence of the vitamin D deficiency linked to a number of health consequences as a concern [3-6]. Evidence from observational studies has linked low vitamin D status with impairment in glucose homeostasis and immune dysfunction [7-9]. However, interventional studies, particularly those focused on paediatric populations, have been limited and inconsistent. There is a need for detailed studies, to clarify the therapeutic benefits of vitamin D in these important clinical areas. Objective: The aims of this PhD thesis were two-fold. Firstly, to perform preliminary work assessing the association between vitamin D deficiency and bone status, glucose homeostasis and immune function, and to explore any changes in these parameters following short term vitamin D3 replacement therapy. Secondly, to assess the effectiveness of an electronic surveillance system (ScotPSU) as a tool to determine the current incidence of hospital-based presentation of childhood vitamin D deficiency in Scotland. Methods: Active surveillance was performed for a period of two years as a part of an electronic web-based surveillance programme performed by the Scottish Paediatric Surveillance Unit (ScotPSU). The validity of the system was assessed by identifying cases with profound vitamin D deficiency (in Glasgow and Edinburgh) from the regional laboratory. All clinical details were checked against those identified using the surveillance system. Thirty-seven children aged 3 months to 10 years, who had been diagnosed with vitamin D deficiency, were recruited for the bone, glucose and immunity studies over a period of 24 months. Twenty-five samples were analysed for the glucose and bone studies; of these, 18 samples were further analysed for immune study. Treatment consisted of six weeks taking 5000 IU units cholecalciferol orally once a day. At baseline and after completion of treatment, 25 hydroxyvitamin D (25(OH)D), parathyroid hormone (PTH), alkaline phosphatase (ALP), collagen type 1 cross-linked C-telopeptide (CTX), osteocalcin (OCN), calcium, phosphate, insulin, glucose, homeostasis model assessment index, estimated insulin resistance (HOMA IR), glycated hemoglobin (HbA1c), sex hormone binding globulin (SHBG), lipids profiles, T helper 1 (Th1) cytokines (interleukin-2 ( IL-2), tumor necrosis factors-alpha (TNF-α), interferon-gamma (INF-γ)), T helper 2 (Th2) cytokines (interleukin-4 (IL-4), interleukin-5 (IL-5), interleukin-6 (IL-6)), T helper 17 (Th17) cytokine (interleukin-17 (IL-17)), Regulatory T (Treg) cytokine (interleukin-10 (IL-10)) and chemokines/cytokines, linked with Th1/Th2 subset balance and/or differentiation (interleukin-8 (IL-8), interleukin-12 (IL-12), eosinophil chemotactic protein ( EOTAXIN), macrophage inflammatory proteins-1beta (MIP-1β), interferon-gamma-induced protein-10 (IP-10), regulated on activation, normal T cell expressed and secreted (RANTES), monocyte chemoattractant protein-1(MCP-1)) were measured. Leukoocyte subset analysis was performed for T cells, B cells and T regulatory cells and a luminex assay was used to measure the cytokiens. Results: Between September 2009 and August 2011, 163 cases of vitamin D deficiency were brought to the attention of the ScotPSU, and the majority of cases (n = 82) were reported in Glasgow. The cross-validation checking in Glasgow and Edinburgh over a one-year period revealed only 3 (11%) cases of clearly symptomatic vitamin D deficiency, which had been missed by the ScotPSU survey in Glasgow. While 16 (67%) symptomatic cases had failed to be reported through the ScotPSU survey in Edinburgh. For the 23 children who are included in bone and glucose studies, 22 (96%) children had basal serum 25(OH)D in the deficiency range (< 50 nmol/l) and one (4%) child had serum 25(OH)D in the insufficiency range (51-75 nmol/l). Following vitamin D3 treatment, 2 (9%) children had final serum 25(OH)D lower than 50 nmol/l, 6 (26%) children had final serum 25(OH)D between >50-75 nmol/l, 12 (52%) children reached a final serum 25(OH)D >75-150 nmol/l and finally 3 (13%) exceeded the normal reference range with a final 25(OH)D >150 nmol/l. Markers for remodelling ALP and PTH had significantly decreased (p = 0.001 and <0.0001 for ALP and PTH respectively). In 17 patients for whom insulin and HOMA IR data were available and enrolled in glucose study, significant improvements in insulin resistance (p = 0.04) with a trend toward a reduction in serum insulin (p = 0.05) was observed. Of those 14 children who had their cytokines profile data analysed and enrolled in the immunity study, insulin and HOMA IR data were missed in one child. A significant increase in the main Th2 secreted cytokine IL-4 (p = 0.001) and a tendency for significant increases in other Th2 secreted cytokines IL-5 (p = 0.05) and IL-6 (p = 0.05) was observed following vitamin D3 supplementation. Conclusion: An electronic surveillance system can provide data for studying the epidemiology of vitamin D deficiency. However, it may underestimate the number of positive cases. Improving vitamin D status in vitamin D deficient otherwise healthy children significantly improved their vitamin D deficient status, and was associated with an improvement in bone profile, improvements in insulin resistance and an alteration in main Th2 secreting cytokines.

Lifestyle factors, adiposity and cardiometabolic risk factors in South Asian women living in Scotland

South Asians migrating to the Western world have a 3 to 5-fold higher risk of developing type 2 diabetes and double the risk of cardiovascular disease (CVD) than the background population of White European descent, without exhibiting a proportional higher prevalence of conventional cardiometabolic risk factors. Notably, women of South Asian descent are more likely to be diagnosed with type 2 diabetes as they grow older compared with South Asian men and, in addition, they have lost the cardio-protective effects of being females. Despite South Asian women in Western countries being a high risk group for developing future type 2 diabetes and CVD, they have been largely overlooked. The aims of this thesis were to compare lifestyle factors, body composition and cardiometabolic risk factors in healthy South Asian and European women who reside in Scotland, to examine whether ethnicity modifies the associations between modifiable environmental factors and cardiometabolic risks and to assess whether vascular reactivity is altered by ethnicity or other conventional and novel CVD risks. I conducted a cross-sectional study and recruited 92 women of South Asian and 87 women of White European descent without diagnosed diabetes or CVD. Women on hormone replacement therapy or hormonal contraceptives were excluded too. Age and body mass index (BMI) did not differ between the two ethnic groups. Physical activity was assessed and with self-reported questionnaires and objectively with the use of accelerometers. Cardiorespiratory fitness was quantified with the predicted maximal oxygen uptake (VO2 max) during a submaximal test (Chester step test). Body composition was assessed with skinfolds measured at seven body sites, five body circumferences, measurement of abdominal subcutaneous (SAT) and visceral adipose tissue (VAT) with the use of magnetic resonance imaging (MRI) and liver fat with the use MR spectroscopy. Dietary density was assessed with food frequency questionnaires. Vascular response was assessed by measuring the response to acetylcholine and sodium nitroprusside with the use of Laser Doppler Imaging with Iontophoresis (LDI-ION) and the response to shear stress with the use of Peripheral Arterial Tonometry (EndoPAT). The South Asian women exhibited a metabolic profile consistent with the insulin resistant phenotype, characterised by greater levels of fasting insulin, lower levels of high density lipoprotein (HDL) and higher levels of triglycerides (TG) compared with their European counterparts. In addition, the South Asians had greater levels of glycated haemoglobin (HbA1c) for any given level of fasting glucose. The South Asian women engaged less time weekly with moderate to vigorous physical activity (MVPA) and had lower levels of cardiorespiratory fitness for any given level of physical activity than the women of White descent. In addition, they accumulated more fat centrally for any given BMI. Notably, the South Asians had equivalent SAT with the European women but greater VAT and hepatic fat for any given BMI. Dietary density did not differ among the groups. Increasing central adiposity had the largest effect on insulin resistance in both ethic groups compared with physical inactivity or decreased cardiorespiratory fitness. Interestingly, ethnicity modified the association between central adiposity and insulin resistance index with a similar increase in central adiposity having a substantially larger effect on insulin resistance index in the South Asian women than in the Europeans. I subsequently examined whether ethnic specific thresholds are required for lifestyle modifications and demonstrated that South Asian women need to engage with MVPA for around 195 min.week-1 in order to equate their cardiometabolic risk with that of the Europeans exercising 150 min.week-1. In addition, lower thresholds of abdominal adiposity and BMI should apply for the South Asians compared with the conventional thresholds. Although the South Asians displayed an adverse metabolic profile, vascular reactivity measured with both methods did not differ among the two groups. An additional finding was that menopausal women with hot flushing of both ethnic groups showed a paradoxical vascular profile with enhanced skin perfusion (measured with LDI-ION) but decreased reactive hyperaemia index (measured with EndoPAT) compared with asymptomatic menopausal women. The latter association was independent of conventional CVD risk factors. To conclude, South Asian women without overt disease who live in Scotland display an adverse metabolic profile with steeper associations between lifestyle risk factors and adverse cardiometabolic outcomes compared with their White counterparts. Further work in exploring ethnic specific thresholds in lifestyle interventions or in disease diagnosis is warranted.