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Dark Skinned youths and vitamin D in Southern Canada - Dissertation 2011

Vitamin D Metabolites in Young Adults of Diverse Ancestry Living in the Greater Toronto Area


By Agnes Gozdzik
A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy
Department of Anthropology University of Toronto
© Copyright by Agnes Gozdzik 2011

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Abstract


Vitamin D plays a critical role in bone metabolism and many cellular and immunological processes, and low vitamin D levels have been associated with several chronic and infectious diseases. Previous studies have reported that many otherwise healthy adults of European ancestry living in Canada have low vitamin D concentrations during the wintertime. However, individuals of non-European ancestry are at a higher risk of having low vitamin D levels. This thesis examined vitamin D status in a sample of young adults of diverse ancestry living in the Greater Toronto Area. In my research I found that:

1) vitamin D levels (measured as 25(OH)D concentrations) are low in Canadian young adults, particularly in those of non-European ancestry;

2) vitamin D intakes, which were estimated to be on average higher than current Health Canada recommendations of 200 International Units (IU) per day, were inadequate to maintain optimal vitamin D levels year-round;

3) vitamin D levels undergo large seasonal changes. Winter 25(OH)D concentrations are substantially lower than those observed during the fall;

4) vitamin D intake is an important year-round predictor of 25(OH)D concentrations, but skin pigmentation and sun exposure are also important predictors during the times when UVB is adequate for cutaneous synthesis; and

5) vitamin D binding protein (VDBP) polymorphisms are significant predictors of 25(OH)D concentrations, but their effects vary by ancestry and season, indicating gene-environment interaction effects.

My research shows that higher vitamin D intakes are needed to offset the seasonal drop in vitamin D levels and to ensure adequate vitamin D levels year-round for those at higher risk of insufficiency.

Figure from the Dissertation

Image

Table of Contents

1 Vitamin D: Background and Introduction.......................1
1.1 Vitamin D: History and Evolutionary Perspective..2
1.1.1 The Discovery of Vitamin D........................2
1.1.2 Evolutionary Development of Vitamin D in Non-vertebrates and Vertebrates......4
1.1.3 The Role of Vitamin D in Human Evolution.........................4
1.2 Vitamin D: General Information..............................9
1.2.1 Vitamin D Sources......9
1.2.2 Photobiology of Vitamin D........................10
1.2.3 Metabolism of Vitamin D..........................11
1.2.4 Factors Influencing Vitamin D Levels.......15
1.2.5 Vitamin D Binding Protein........................16
1.3 Assessing Vitamin D Levels.17
1.3.1 Normal Vitamin D Status...........................17
1.3.2 Official Vitamin D Recommendations......18
1.3.3 "Normal" Vitamin D Status in Human Evolution...............20
1.4 Health Effects of Vitamin D.23
1.4.1 Skeletal Diseases.......24
1.4.3 Autoimmune Conditions ............................ 26
1.4.4 Cardiovascular Disease .............................. 28
1.4.5 Innate Immunity and Infections ................. 28
1.4.6 Summary of Health Effects........................ 30
1.5 Summary of Vitamin D Status in the Northern Hemisphere ........... 31
1.5.1 Current Vitamin D Status in Canada ......... 31
1.5.2 Current Vitamin D Status in the United States .................... 32
1.5.3 Vitamin D Status in East Asia, Europe and South Asia ...... 34
1.5.4 East Asia ................... 34
1.5.5 Europe ....................... 35
1.5.6 South Asia ................. 38
1.6 Rationale for Study and Study Goals ..................... 39
1.7 References ... 42

Chapter 2 .....(Student was co-author on previous publication)............ 55

2 Low Wintertime Vitamin D Levels in a Sample of Healthy Young Adults of Diverse Ancestry Living in the Toronto area:
  Associations with Vitamin D Intake and Skin
Pigmentation.. 55
2.1 Abstract ....... 56
2.2 Introduction . 57
2.3 Materials and Methods.......... 59
2.3.1 Study Population and Recruitment ............ 59
2.3.2 Data Collection.........60
2.3.3 Measuring Pigmentation using Reflectometry..................... 60
2.3.4 Biochemical Analyses................................ 61
2.3.5 Nutritional Analyses . 61
2.3.6 Statistical Analyses...62
2.4.1 Sample Characteristics............................... 62
2.4.2 Vitamin D Status and Ancestry..................63
2.4.3 Vitamin D Intake and Ancestry ................. 64
2.4.4 Factors Affecting Vitamin D Status...........64
2.4.5 Figures.......................66
2.4.6 Tables ........................ 67
2.5 Discussion...71
2.6 Conclusion .. 73
2.7 Competing Interests..............73
2.8 Author's Contributions.........73
2.9 Acknowledgments................. 74
2.10References ... 75

Chapter 3 .......(Student was co-author on previous publication)........ 79

3 Serum 25-hydroxyvitamin D Concentrations Fluctuate Seasonally in Young Adults of Diverse Ancestry Living in Toronto ..79
3.1 Abstract.......80
3.2 Introduction . 80
3.3 Participants and Methods ...... 82
3.3.1 Study Population and Recruitment............82
3.3.2 Data Collection.........82
3.3.3 Sun Exposure ............ 83
3.3.4 Measuring Pigmentation Using Reflectometry.................... 83
3.3.5 Biochemical Analyses................................ 84
3.3.6 Nutritional Analyses . 85
3.3.7 Statistical Analyses ... 85
3.4.1 Sample Characteristics............................... 86
3.4.2 Serum 25(OH)D Concentrations Stratified by Ancestry.....86
3.4.3 Seasonal Variation in 25(OH)D.................87
3.4.4 Vitamin D Intake.......87
3.4.5 Factors Affecting Vitamin D Status...........88
3.4.6 Figures.......................90
3.4.7 Tables ........................ 92
3.5 Discussion ... 95
3.6 Acknowledgements.............100
3.7 References.101

Chapter 4 ...(Student was co-author on previous publication).... 106

4 Association of Vitamin D Binding Protein (VDBP) Polymorphisms and Serum 25(OH)D Concentrations in a Sample of Young Canadian Adults of Different Ancestry..106
4.1 Abstract.....107
4.2 Introduction.........................107
4.3 Materials and Methods........110
4.3.1 Participants.............. 110
4.3.2 25(OH)D Measurement...........................110
4.3.3 Anthropometric Measurements................ 112
4.3.4 Ancestry .................. 112
4.3.5 Dietary Assessment.112
4.3.6 DNA Collection and Genetic Analysis....112
4.3.7 Sun/UVR Exposure.113
4.3.8 Skin Pigmentation ... 113
4.3.9 Statistical Analyses . 114
4.4.1 Sample Characteristics, 25(OH)D Concentrations and Associated Variables.... 115
4.4.2 Vitamin D Binding Protein (VDBP) Polymorphisms, Ancestry and 25(OH)D Levels......................116
4.4.3 Relative Role of Vitamin D Intake, Skin Pigmentation, Sun Exposure and GC Polymorphisms on 25(OH)D Concentrations....................117
4.4.4 Tables ...................... 119
4.5 Discussion.124
4.6 Acknowledgements ............. 129
4.7 References . 130
Chapter 5...............134
5 Concluding Remarks .................. 134
5.1 Introduction ......................... 135
5.2 Summary of Findings.......... 135
5.2.1 Vitamin D Levels in Canadian Young Adults of Diverse Ancestry...................135
5.2.2 Vitamin D Intake in Young Adults of Diverse Ancestry...136
5.2.3 Seasonal Trends in Vitamin D Levels.....137
5.2.4 Impact of Various Factors Affecting Vitamin D Levels....137
5.2.5 Effect of Genetic Variants of Vitamin D Binding Protein on Vitamin D levels 138
5.3 Conclusions.........................138
5.4 References.140
Bibliography.........141
5.3 Conclusions

Clipped from conclusions

One of the major conclusions derived from my research is that higher vitamin D intakes are needed to offset the seasonal drop in vitamin D levels and to ensure adequate vitamin D levels year-round for those at higher risk of insufficiency. In this sense, my study lends support to the recent recommendations of the Canadian Cancer Society, which take into account risk factors for vitamin D insufficiency (seasonality, UVR exposure and skin pigmentation). The Canadian Cancer Society recommends an intake of 1000 IU per day during the fall and winter, or year-round for those at higher risk of having low vitamin D levels (those with darker skin, who stay indoors or always cover up) (Society, 2007). While an increase in vitamin D intake, particularly during the winter, is clearly needed, further work is required to elucidate the vitamin D intakes that are necessary to achieve and maintain optimal vitamin D levels in individuals of different ancestry.

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See also VitaminDWiki

Attached files

ID Name Comment Uploaded Size Downloads
796 Gozdzik1.png Chart from Dissertation admin 01 Oct, 2011 15:46 187.64 Kb 1601
795 Vitamin D for dark skin youths in Canada - Gozdzik PhD Thesis 2011.pdf Dissertation admin 01 Oct, 2011 15:37 1.12 Mb 1316
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