Vitamin D deficiency and secondary hyperparathyroidism and the association with bone mineral density in persons with Pakistani and Norwegian background living in Oslo, Norway: The Oslo Health Study
Introduction
Vitamin D is important for adequate calcium absorption. Reduced calcium absorption due to vitamin D deficiency may result in increased parathyroid hormone (PTH) secretion to maintain calcium homeostasis. Vitamin D deficiency may thus lead to secondary hyperparathyroidism (2.HPT) [1], [2]. The classical outcomes of severe vitamin D deficiency are rickets and osteomalacia [2]. Low vitamin D has also been related to low bone density and osteoporotic fractures [3], [4], [5], [6].
In Western countries, there is a large number of immigrants from South Asia. However, surprisingly few studies have assessed vitamin D status in these immigrant populations. Studies from Britain suggest that immigrants from Pakistan/The Indian subcontinent are at great risk of serious vitamin D deficiency [7], [8]. In Oslo, two smaller studies have reported poor vitamin D status in younger Pakistani women [9], [10]. Except for a smaller American study in young women [11] and a British study in Indo-Asian patients admitted to a rheumatology clinic [12], we are not aware of any study assessing the association between vitamin D deficiency and bone density in immigrants from South Asia.
The Norwegian capital of Oslo with 500 000 inhabitants has an immigrant population from non-western countries of nearly 70 000 persons, and of these, around 20 000 are of Pakistani origin. The Pakistanis started to move to Oslo in the 1970s as labor immigrants. In connection with the large Oslo Health Study, we had the opportunity to study the prevalence of poor vitamin D status and 2.HPT and the association with bone density in Norwegian born and Pakistani born men and women living in Oslo, Norway.
Section snippets
Materials and methods
In 2000–2001, the Oslo Health Study—a population-based multipurpose study inviting all individuals in Oslo County born in 1970, 1960, 1955, 1940–1941, and 1924–1925—was conducted under the joint collaboration of the National Health Screening Service of Norway (now the Norwegian Institute of Public Health), the University of Oslo and the Municipality of Oslo. The overall attendance rate was 46% (n = 18 770), varying from 36% in those 30 years old to 55% in those 59–60 years old.
Baseline
25(OH)D and ethnicity
Mean serum 25(OH)D concentration was 74.8 ± 23.7 nmol/l in persons born in Norway compared to 25.0 ± 13.6 nmol/l in persons born in Pakistan (P = 0.000). The distribution of 25(OH)D was very different in the two ethnic groups (Fig. 1). In men and women born in Norway, 86% had 25(OH)D levels of 50 nmol/l or higher, whereas only 8% of the Pakistani men and 10% of the Pakistani women achieved these levels. None of the Norwegian-born had 25(OH)D levels below 12.5 nmol/l, whereas 9% of Pakistani men
Discussion
In this study from Oslo, the prevalence of serious vitamin D deficiency defined as secondary hyperparathyroidism was four times higher in women with Pakistani background compared to women with Norwegian background. Also in Pakistani men, serious vitamin D deficiency was prevalent, and five times as frequent as in men with Norwegian background. Both in Pakistani women and men the prevalence was high even in the younger age groups. However, the influence on the skeleton differed. Whereas BMD was
Acknowledgements
The data collection was performed by the National Health Screening Service of Norway—now the Norwegian Institute of Public Health. Blood analyses were economically supported by Eckbos Foundation, Oslo and Forskningsforum Aker University Hospital and the bone densitometry by the Research Council of Norway.
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