Adequate vitamin D status plays an important role in bone health and may also protect against Type 1 Diabetes (T1D), multiple sclerosis and certain cancers. Vitamin D is obtained from two sources; diet and through skin synthesis through the action of ultraviolet (UV) light. Dietary intakes of vitamin D are low in New Zealand (NZ) and the majority of our vitamin D comes from UV exposure. The NZ population may be at risk of low vitamin D status because of low dietary intakes, the country�s latitude (35-46 �S), and high proportion of darker skinned Maori and Pacific People. While case reports have described the occurrence of rickets, predominantly in immigrant groups, there are currently no national data on the vitamin D status of the NZ population. Reports of low vitamin D status in countries of similar latitude to NZ justify an examination of New Zealanders� vitamin D status. The best method to assess of vitamin D status is to measure circulating 25-hydroxyvitamin D concentrations. This thesis comprises three main studies. The first two had the following aims: to measure 25-hydroxyvitamin D concentrations and their determinants in a national sample (n=1585) of NZ children aged 5-14 y and to measure serum 25-hydroxyvitamin D concentrations and their determinants in a national sample (n=2948) of New Zealanders aged 15 y and over. The 2002 Children�s Nutrition Survey CNS02 was a year long (December, March-November) cross-sectional survey of a nationally representative sample of NZ school children 5-14 y. Over-sampling of Maori and Pacific children allowed ethnic specific analyses. The 1997 National Nutrition Survey (NNS97) participants were recruited over one year according to an area-based sampling frame with a 3 stage stratified design consisting of primary sampling units, households within each unit, and one randomly selected respondent from each household. Mean (99% CI) serum 25-hydroxyvitamin D concentrations were similar in children and adults (both 50 nmol/L). Among Maori, Pacific and NZEO children respectively, prevalence (%, 99% CI) of serum 25-hydroxyvitamin D deficiency (< 17.5 nmol/L) was 5% (2, 12), 8% (5, 14), and 3% (1,7). Based on a cutoff of < 37.5 nmol/L, prevalence of insufficiency was 41% (29, 53), 59% (42, 75) and 25% (15, 35), respectively. Based on a cutoff of 50 nmol/L, 56% of children were insufficient. Three percent of adult New Zealanders had serum 25-hydroxyvitamin D concentrations indicative of deficiency ([less than or equal to] 17.5 nmol/L); 48% and 84% were insufficient based on cutoffs of [less than or equal to] 50 and [less than or equal to] 80 nmol/L The main determinants of vitamin D status in NZ children were season, ethnicity and sex. After adjustment for other factors and covariates, boys had an adjusted mean (99% CI) 25-hydroxyvitamin D concentration 5 (1, 9) nmol/L higher than girls, Maori children were 7 (2, 11) and Pacific children 15 (11, 20) nmol/L lower than NZ European and Other (NZEO) children. Obese children were 7 (2, 11) nmol/L lower than overweight or �normal� weight. Children�s mean 25-hydroxyvitamin D concentrations (adjusted for other variables) peaked in March (69 nmol/L) and was at its lowest in August (36 nmol/L). In adults, there were effects of a similar magnitude of ethnicity and season on serum 25-hydroxyvitamin D concentrations. Obesity, latitude and age were determinants of vitamin D status in women but not men. Obese (BMI > 30) women had an adjusted mean vitamin concentration 6 (3, 10) nmol/L lower than women with BMI < 25. Women living in the South Island were 6 (3, 9) nmol/L lower than women living in the North Island. Additionally, adjusted mean serum 25-hydroxyvitamin D was 13 (8, 18) higher in women 15 -18 y than women 65 y or older. The third and final study aimed to determine whether the higher rates of vitamin D inadequacy reported in the winter than summer months in NZ also result in higher PTH concentrations, which would provide evidence for functional effect of inadequate vitamin D status. We also aimed to objectively explore the effect of natural skin colour on vitamin D status, given the higher prevalence of vitamin D insufficiency in dark-skinned groups living far from the equator. Skin colour measurements were taken with a hand-held light reflectometer (Datacolor Mercury[TM] 1000 colorimeter, Lawrenceville, NJ). In the 342 residents of Invercargill and Dunedin, mean serum 25-hydroxyvitamin D concentrations were lower in the late summer versus early spring (79 vs 51 nmol/L; P< 0.001). The lower serum 25-hydroxyvitamin D in early spring versus summer was associatedwith a 2 pg/mL (P< 0.001) higher parathyroid hormone (PTH) concentration. Interestingly, no significant effect of natural skin colour, based on light reflectance at the inside of the upper arm, was discovered, though there was a positive effect of tanning, based on light reflectance at the upper forearm, on serum 25-hydroxyvitamin D concentrations. Ethnicity and season are major determinants of serum 25-hydroxyvitamin D in New Zealanders. There is a high prevalence of vitamin D insufficiency in NZ children and adults, which may contribute to increased risk of osteoporosis and other chronic disease. While there is a pressing need for more convincing evidence with regards to the health risks associated with the low vitamin D status in children, evidence from the study of adults, where higher PTH concentrations were found during spring versus summer, suggests that the low 25-hydroxyvitamin D concentrations are having an adverse effect on bone health of adults. The high prevalence of vitamin D insufficiency in New Zealanders, warrants serious consideration of strategies such as fortification, to improve the vitamin D status of the population.

Thesis (M.S.)--University of Wyoming, 2008. / Title from PDF title page (viewed on Dec. 4, 2009). Includes bibliographical references (p. 75-88).

Adequate vitamin D status plays an important role in bone health and may also protect against Type 1 Diabetes (T1D), multiple sclerosis and certain cancers. Vitamin D is obtained from two sources; diet and through skin synthesis through the action of ultraviolet (UV) light. Dietary intakes of vitamin D are low in New Zealand (NZ) and the majority of our vitamin D comes from UV exposure. The NZ population may be at risk of low vitamin D status because of low dietary intakes, the country�s latitude (35-46 �S), and high proportion of darker skinned Maori and Pacific People. While case reports have described the occurrence of rickets, predominantly in immigrant groups, there are currently no national data on the vitamin D status of the NZ population. Reports of low vitamin D status in countries of similar latitude to NZ justify an examination of New Zealanders� vitamin D status. The best method to assess of vitamin D status is to measure circulating 25-hydroxyvitamin D concentrations. This thesis comprises three main studies. The first two had the following aims: to measure 25-hydroxyvitamin D concentrations and their determinants in a national sample (n=1585) of NZ children aged 5-14 y and to measure serum 25-hydroxyvitamin D concentrations and their determinants in a national sample (n=2948) of New Zealanders aged 15 y and over. The 2002 Children�s Nutrition Survey CNS02 was a year long (December, March-November) cross-sectional survey of a nationally representative sample of NZ school children 5-14 y. Over-sampling of Maori and Pacific children allowed ethnic specific analyses. The 1997 National Nutrition Survey (NNS97) participants were recruited over one year according to an area-based sampling frame with a 3 stage stratified design consisting of primary sampling units, households within each unit, and one randomly selected respondent from each household. Mean (99% CI) serum 25-hydroxyvitamin D concentrations were similar in children and adults (both 50 nmol/L). Among Maori, Pacific and NZEO children respectively, prevalence (%, 99% CI) of serum 25-hydroxyvitamin D deficiency (< 17.5 nmol/L) was 5% (2, 12), 8% (5, 14), and 3% (1,7). Based on a cutoff of < 37.5 nmol/L, prevalence of insufficiency was 41% (29, 53), 59% (42, 75) and 25% (15, 35), respectively. Based on a cutoff of 50 nmol/L, 56% of children were insufficient. Three percent of adult New Zealanders had serum 25-hydroxyvitamin D concentrations indicative of deficiency ([less than or equal to] 17.5 nmol/L); 48% and 84% were insufficient based on cutoffs of [less than or equal to] 50 and [less than or equal to] 80 nmol/L The main determinants of vitamin D status in NZ children were season, ethnicity and sex. After adjustment for other factors and covariates, boys had an adjusted mean (99% CI) 25-hydroxyvitamin D concentration 5 (1, 9) nmol/L higher than girls, Maori children were 7 (2, 11) and Pacific children 15 (11, 20) nmol/L lower than NZ European and Other (NZEO) children. Obese children were 7 (2, 11) nmol/L lower than overweight or �normal� weight. Children�s mean 25-hydroxyvitamin D concentrations (adjusted for other variables) peaked in March (69 nmol/L) and was at its lowest in August (36 nmol/L). In adults, there were effects of a similar magnitude of ethnicity and season on serum 25-hydroxyvitamin D concentrations. Obesity, latitude and age were determinants of vitamin D status in women but not men. Obese (BMI > 30) women had an adjusted mean vitamin concentration 6 (3, 10) nmol/L lower than women with BMI < 25. Women living in the South Island were 6 (3, 9) nmol/L lower than women living in the North Island. Additionally, adjusted mean serum 25-hydroxyvitamin D was 13 (8, 18) higher in women 15 -18 y than women 65 y or older. The third and final study aimed to determine whether the higher rates of vitamin D inadequacy reported in the winter than summer months in NZ also result in higher PTH concentrations, which would provide evidence for functional effect of inadequate vitamin D status. We also aimed to objectively explore the effect of natural skin colour on vitamin D status, given the higher prevalence of vitamin D insufficiency in dark-skinned groups living far from the equator. Skin colour measurements were taken with a hand-held light reflectometer (Datacolor Mercury[TM] 1000 colorimeter, Lawrenceville, NJ). In the 342 residents of Invercargill and Dunedin, mean serum 25-hydroxyvitamin D concentrations were lower in the late summer versus early spring (79 vs 51 nmol/L; P< 0.001). The lower serum 25-hydroxyvitamin D in early spring versus summer was associatedwith a 2 pg/mL (P< 0.001) higher parathyroid hormone (PTH) concentration. Interestingly, no significant effect of natural skin colour, based on light reflectance at the inside of the upper arm, was discovered, though there was a positive effect of tanning, based on light reflectance at the upper forearm, on serum 25-hydroxyvitamin D concentrations. Ethnicity and season are major determinants of serum 25-hydroxyvitamin D in New Zealanders. There is a high prevalence of vitamin D insufficiency in NZ children and adults, which may contribute to increased risk of osteoporosis and other chronic disease. While there is a pressing need for more convincing evidence with regards to the health risks associated with the low vitamin D status in children, evidence from the study of adults, where higher PTH concentrations were found during spring versus summer, suggests that the low 25-hydroxyvitamin D concentrations are having an adverse effect on bone health of adults. The high prevalence of vitamin D insufficiency in New Zealanders, warrants serious consideration of strategies such as fortification, to improve the vitamin D status of the population.

Thesis (Ph.D.)--University of Adelaide, Dept. of Physiology, 2003? / Includes bibliographical references (leaves 226-273.). Also available in an electronic version.

Thesis (Ph.D.)--University of Adelaide, Dept. of Physiology, 2002. / Includes bibliographical references. Also available in a print form.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 95-105).

No description available.

Thesis (M.S.)--University of Massachusetts Amherst, 2008. / Includes bibliographical references (p. 58-62).

Inaugural address delivered on 2 November 2011 / Marietjie Herselman was born in the Langkloof, where she matriculated at the McLachlan High School. She obtained a BSc (Physiology and Dietetics) degree at Stellenbosch University and for the next 18 years worked as a dietitian at Tygerberg Hospital, where she specialised in renal nutrition. She obtained a master’s degree in nutrition in 1985 and in 1991 was appointed as a lecturer in the Department of Human Nutrition, Faculty of Health Sciences, at Stellenbosch University. In the same year she obtained her PhD in nutritional sciences at this university, where she was later promoted to senior lecturer (1995), associate professor (2001) and full professor (2010). From 2008 to 2010 she was appointed first as acting head and later as head of the Division of Human Nutrition. She served on the Professional Board of Dietetics from 1998 to 2003 and also on various sub-committees of the Board. She regularly reviews papers and research applications for scientific councils/associations as well as five national and four international scientific journals. Currently, she serves on the editorial boards of four international scientific journals and in 2008 she was elected as the co-editor (Africa region) of the international journal Nutrition. She successfully delivered 17 master’s students and published 29 scientific papers in national and international journals and three chapters in textbooks. Marietjie also presented papers at 19 international and 37 national conferences. Three international and four national awards were bestowed on her for her research in renal nutrition. She played a leading role in the initiation of the Community Nutrition Security Project (CNSP) in the Breede Valley, as part of Stellenbosch University’s HOPE Project, as well as the NOMA master’s programme in Nutrition, Human Rights and Governance in collaboration with the universities of Oslo and Akershus (Norway) as well as Makerere and Kyambogo (Uganda).

Primarily synthesised via cutaneous exposure to solar ultraviolet B (UVB) radiation, serum vitamin D concentrations, measured as 25-hydroxyvitamin D (25(OH)D), fluctuate according to solar availability. Seasonal variations in vitamin D are common in areas of high or low latitude determined by the distance from the sun. Seasonal variations in blood pressure, immune markers and some diseases including influenza, have also been reported. However, the contributions of UVB light or vitamin D on the immune markers have not been fully determined. Against this background, the purpose of this research was to investigate the effects of UVB light therapy and dietary vitamin D supplementation on markers of immune function. The D SIRe1 study aimed to assess whether dietary-derived 25(OH)D could have similar effects on immune function as light-derived 25(OH)D. The study was an 8-week comparative intervention trial in healthy adults randomised to receive either 3 times weekly UVB radiation (equivalent to doses received during a Grampian-summer) for 4 weeks; or oral vitamin D3 (1000 IU a day for 8 weeks). Total 25(OH)D was measured by dual tandem mass spectrometry of serum samples following removal of protein and de-lipidation, whilst regulatory T cells (Tregs), known for maintaining immune system homeostasis, by flow cytometry. The study showed similar short-term effects between oral vitamin D and UVB exposure on measured outcomes. However, study interpretation was limited by the lack of a placebo group, yet, to our knowledge, this was the first study to directly compare dose-matched UVB therapy and vitamin D supplementation in healthy participants. Using similar laboratory techniques, the D-SIRe2 study, a placebo-controlled trial, assessed short-term (12 weeks) and long-term (43 weeks) effects of vitamin D supplementation on immune markers. Commencing in spring (March) and finishing in winter (January) 2015/2016, the study showed seasonal fluctuations in most immune markers. The fluctuations did not change according to variations in 25(OH)D concentrations nor were they correlated with solar UVB doses, with the exception of T cell proliferative responses, which were positively correlated with daily solar UVB doses. An interesting finding from this study was the prevention of increases in pro-inflammatory IFN-γ cytokine concentrations in the spring and summer time in the vitamin D3 supplemental group versus placebo. IFN-γ concentrations were raised from 7940 pg/mL at baseline in March, to roughly 12400 pg/mL at week 4 and to 13909 pg/mL at week 12 in the placebo group. The concentrations were roughly 1.3 times the mean concentrations measured in the vitamin D group at the timepoints following baseline concentrations of 10678 pg/mL, and 10013 pg/mL and 10233 pg/mL at weeks 4 and 12, respectively. The interactions between solar light or seasonal effects and oral vitamin D supplementation, as well as their individual and combined effects on immune function, are yet to be fully determined. Moreover, the metabolic and physiological implications of seasonal variation in serum 25(OH)D concentration and markers of immune function are currently unknown, requiring further investigation.