Research article

Pakistanis living in Oslo have lower serum 1,25-dihydroxyvitamin D levels but higher serum ionized calcium levels compared with ethnic Norwegians. The Oslo Health Study

Kristin Holvik¹ , Haakon E Meyer^1,2 , Anne Johanne Søgaard^2,1 , Egil Haug³ and Jan A Falch³

¹Institute of General Practice and Community Medicine, University of Oslo, PO Box 1130 Blindern, NO-0318 Oslo, Norway

²Division of Epidemiology, Norwegian Institute of Public Health, Oslo, Norway

³Center of Endocrinology, Aker University Hospital, and Faculty of Medicine, University of Oslo, Norway

author email corresponding author email

BMC Endocrine Disorders 2007, 7:9doi:10.1186/1472-6823-7-9

Published:	18 October 2007

Abstract

Background

Persons of Pakistani origin living in Oslo have a much higher prevalence of vitamin D deficiency and secondary hyperparathyroidism but similar bone mineral density compared with ethnic Norwegians. Our objective was to investigate whether Pakistani immigrants living in Oslo have an altered vitamin D metabolism by means of compensatory higher serum levels of 1,25-dihydroxyvitamin D (s-1,25(OH)₂D) compared with ethnic Norwegians; and whether serum levels of ionized calcium (s-Ca²⁺) differ between Pakistanis and Norwegians.

Methods

In a cross-sectional, population-based study venous serum samples were drawn from 94 Pakistani men and 67 Pakistani women aged 30–60 years, and 290 Norwegian men and 270 Norwegian women aged 45–60 years; in total 721 subjects.

Results

Pakistanis had lower s-1,25(OH)₂D compared with Norwegians (p < 0.001). Age- and gender adjusted mean (95% CI) levels were 93 (86, 99) pmol/l in Pakistanis and 123 (120, 126) pmol/l in Norwegians, p < 0.001. The difference persisted after controlling for body mass index. There was a positive relation between serum 25-hydroxyvitamin D (s-25(OH)D) and s-1,25(OH)₂D in both groups. S-Ca²⁺ was higher in Pakistanis; age-adjusted mean (95% CI) levels were 1.28 (1.27, 1.28) mmol/l in Pakistanis and 1.26 (1.26, 1.26) mmol/l in Norwegians, p < 0.001. In both groups, s-Ca²⁺ was inversely correlated to serum intact parathyroid hormone levels (s-iPTH). For any s-iPTH, s-Ca²⁺ was higher in Pakistanis, also when controlling for age.

Conclusion

Community-dwelling Pakistanis in Oslo with low vitamin D status and secondary hyperparathyroidism have lower s-1,25(OH)₂D compared with ethnic Norwegians. However, the Pakistanis have higher s-Ca²⁺. The cause of the higher s-Ca²⁺ in Pakistanis in spite of their higher iPTH remains unclear.