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Abstract

Most of our vitamin D comes from the action of ultraviolet light on skin.¹ People with a darker skin produce less vitamin D for a given sunlight exposure,^1,2 and veiled women, regardless of the climate, are at a high risk of vitamin D deficiency because of their reduced skin exposure to sunlight.^3-6 In pregnant women there is the added risk of vitamin D deficiency in the baby.

We screened veiled or dark-skinned pregnant women attending an antenatal clinic at a major metropolitan teaching hospital in Melbourne, Victoria, to determine their vitamin D status.

Methods

Subjects

Veiled and/or dark-skinned women attending the antenatal clinic at the Royal Women's Hospital, Melbourne, were advised that they were at increased risk of vitamin D deficiency, putting them at risk of osteomalacia and their children at risk of vitamin D deficiency related problems. Over a 10-month period (July 1999 - April 2000), all such women were asked to provide a blood sample so that their serum level of 25-hydroxyvitamin D₃ (25OHD₃) could be measured. Those who consented were given a pathology request form for a blood sample to be taken.

Assay

Serum samples were stored at - 20ºC, and the 25OHD₃ assays were performed in batches in the complex chemistry laboratory at the Royal Children's Hospital, Melbourne, using the Incstar radioimmunoassay kit (Dade Behring, Melbourne). The reference range for this test was 22.5-93.8 nmol/L. The coefficient of variation between successive assays at a mean concentration of 43.9 nmol/L was 11.7%. The assay fulfilled the acceptability criteria of the Royal College of Pathologists of Australasia endocrinology quality assurance program.

Risk assessment

We recorded the date the blood sample was taken (summer was defined as November to April, and winter as May to October); the patient's facial skin colour (fair, intermediate or very dark skinned); and the degree and consistency of skin covering (women who covered their arms and wore a veil or scarf over their hair and neck at all times when outdoors were coded as "consistently covered"; those who uncovered in a private, outdoor environment as "inconsistently covered"; and those who did not generally cover their arms, hair and neck when outdoors as "uncovered").

Results

Of 94 veiled or dark-skinned women attending the clinic during the study period, 82 had a blood sample taken. Two did not agree to be tested, and the remaining women did not go to have a blood sample taken. Serum levels of 25OHD₃ are shown in Box 1. The median value was 14 nmol/L (range, 3-77 nmol/L). In 66 women (80%) the vitamin D level was below the reference level (< 22.5 nmol/L).

Of the women with values below 22.5 nmol/L, 66% (21/32) had blood samples collected in summer and 90% (45/50) in winter (95% CI for difference, 6%-43%; P < 0.01 by ² test).

Information on skin colour and covering was complete for 70 of the 82 women. The proportion of women with serum 25OHD₃ values below 22.5 nmol/L, according to skin colour and covering, is shown in Box 2. Although numbers in some subgroups were extremely small, it did not appear that this additional information was helpful for clinical management. Among the 12 women with missing information, 11 (92%) had vitamin D levels under 22.5 nmol/L, and nine were tested in winter.

Discussion

Of the dark-skinned and/or veiled pregnant women we tested, 80% were at high risk of vitamin D deficiency, with serum 25OHD₃ values below the reference range. The number of veiled and/or dark-skinned pregnant women attending the Royal Women's Hospital each year is not recorded, but, if they were evenly distributed among the five weekly clinics (as appears likely), we estimate that around 560 such women would attend each year.

Inadequate sunlight exposure can occur even in Australia, especially among women with a modest dress code or those who limit sunlight exposure for other reasons (eg, valid concerns about the risk of skin cancer). However, vitamin D deficiency can be prevented or treated with dietary supplements. Dark-skinned or veiled women should be screened for vitamin D deficiency and those who are deficient should be given vitamin D supplements, whether or not they are pregnant, because of their high risk of bone disease. Their children are also at risk of vitamin D deficiency and their infants, if breast fed, should be given suitable infant vitamin D supplements (Penta-vite, Roche).

We did not measure maternal parathyroid hormone (PTH) levels during the period of this audit, but now do so routinely. PTH is an important marker of bone health in the mother, and there is some evidence that fetal growth is inversely related to maternal PTH level and positively related to maternal calcium level at delivery.⁷

Research is needed to determine the optimal vitamin D level in pregnant women, in terms of outcome for themselves and their offspring, and to determine whether other groups of women are also vitamin D deficient. Data from Queensland (Associate Professor John McGrath, Director, Department of Psychiatry, University of Queensland, Brisbane, personal communication⁸) and from the Geelong Osteoporosis Study (Dr Julie Pasco, Study Coordinator, personal communication) suggest that vitamin D deficiency in women of reproductive age is not limited to specific ethnic or cultural groups.

Acknowledgements

We thank Peter Vervaart and Rhonda Greaves for undertaking the laboratory assays and staff in the Monday clinic at the Royal Women's Hospital for their help. Ruth Morley is supported by the Victorian Health Promotion Foundation (VicHealth).

References

1. Norman AW. Sunlight, season, skin pigmentation, vitamin D, and 25-hydroxyvitamin D: integral components of the vitamin D endocrine system. Am J Clin Nutr 1998; 67: 1108-1110.
2. Feleke Y, Abdulkadir J, Mshana R, et al. Low levels of serum calcidiol in an African population compared with a North European population. Eur J Endocrinol 1999; 141: 358-360.
3. el-Sonbaty MR, Abdul-Ghaffar NU. Vitamin D deficiency in veiled Kuwaiti women. Eur J Clin Nutr 1996; 50: 315-318.
4. Ghannam NN, Hammami MM, Bakheet SM, Khan BA. Bone mineral density of the spine and femur in healthy Saudi females: relation to vitamin D status, pregnancy, and lactation. Calcif Tissue Int 1999; 65: 23-28.
5. Taha SA, Dost SM, Sedrani SH. 25-Hydroxyvitamin D and total calcium: extraordinarily low plasma concentrations in Saudi mothers and their neonates. Pediatr Res 1984; 18: 739-741.
6. Gannage-Yared MH, Chemali R, Yaacoub N, Halaby G. Hypovitaminosis D in a sunny country: relation to lifestyle and bone markers. J Bone Miner Res 2000; 15: 1856-1862.
7. Brunvand L, Quigstad E, Urdal P, Haug E. Vitamin D deficiency and fetal growth. Early Hum Dev 1996; 45: 27-33.
8. McGrath JJ, Kimlin MG, Saha S, et al. Vitamin D insufficiency in south-east Queensland [letter]. Med J Aust. 2001; 174: 150-151.

Authors' details

Clinical Epidemiology and Biostatistics Unit, Murdoch Children's Research Institute, and University of Melbourne Department of Paediatrics, Royal Children's Hospital, Melbourne, VIC.
Ruth Morley, MB BChir, FRCPCH, Senior Research Fellow.

Reprints will not be available from the authors.
Correspondence: Dr Ruth Morley, Clinical Epidemiology and Biostatistics Unit, Murdoch Children's Research Institute, and University of Melbourne Department of Paediatrics, Royal Children's Hospital, Flemington Road, Parkville, VIC 3052.
morleyrATcryptic.rch.unimelb.edu.au

©MJA 2001
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