Clin Rheumatol (2007) 26: 182–185 DOI 10.1007/s10067-006-0258-6
ORIGINA L ARTI CLE
H. C. Chong . S. S. Chee . E. M. L. Goh . S. K. Chow . S. S. Yeap
Dietary calcium and bone mineral density in premenopausal women with systemic lupus erythematosus Received: 26 December 2005 / Revised: 12 February 2006 / Accepted: 14 February 2006 / Published online: 25 March 2006 # Clinical Rheumatology 2006
Abstract The primary objective of this study was to determine the relationship between dietary calcium intake and bone mineral density (BMD) in premenopausal women with systemic lupus erythematosus (SLE) on corticosteroids (CS). The secondary aim was to identify other risk factors for osteoporosis in these patients. A cross-sectional sample of patients attending the SLE Clinic at a teaching hospital was recruited. BMD was measured using dualenergy X-ray absorptiometry. Daily dietary calcium intake was assessed using a structured validated food frequency questionnaire, in which patients were asked to estimate their food intake based on their recent 2-month dietary habits. Sixty subjects were recruited with a mean age of 33.70±8.46 years. The median duration of CS use was 5.5 years (range 0.08–24). The median cumulative dose of steroids was 17.21 g (range 0.16–91.37). The median daily dietary calcium intake was 483 mg (range 78–2101). There was no significant correlation between calcium intake and BMD, even after correcting for CS use. There were also no correlations between BMD and the duration of SLE, cumulative CS use, duration of CS use, smoking, alcohol intake, and SLE disease activity index score. Twenty-eight (46.7%) patients had normal BMD, 28 (46.7%) had osteopenia, and four (6.6%) had osteoporosis. Duration of SLE significantly correlated with cumulative CS dosage. H. C. Chong . E. M. L. Goh . S. K. Chow . S. S. Yeap Department of Medicine, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia S. S. Chee Department of Nutrition and Dietetics, Faculty of Allied Health Sciences, University Kebangsaan Malaysia, Kuala Lumpur, Malaysia S. S. Yeap (*) Subang Jaya Medical Centre, No. 1, Jalan SS 12/1A, 47500 Subang Jaya, Selangor, Malaysia e-mail:
[email protected] Tel.: +60-3-56306315 Fax: +60-3-56306321
In conclusion, 6.7% of these Asian premenopausal SLE women had osteoporosis and only 46.7% had normal BMD. Daily dietary calcium intake did not correlate with BMD. Keywords Bone mineral density . Calcium . Corticosteroid . Osteoporosis . SLE
Introduction Systemic lupus erythematosus (SLE) is a chronic, multisystemic autoimmune disease of young women in the reproductive age group. Corticosteroids (CS) are the mainstay of treatment in SLE. Whether it is the CS treatment or the disease itself per se, osteoporosis is being increasingly recognized in SLE patients. Studies on Caucasian females with SLE have shown that they have lower BMD and higher fracture risks than the healthy population [1]. There have been several studies looking at BMD in premenopausal SLE patients, with conflicting results on the effects of CS on BMD [2–10]. Some have shown an adverse effect of CS on BMD [4, 6, 7, 9, 10] whereas others have shown no effect [2, 3, 5, 8]. Dietary calcium has been positively associated with bone mass in premenopausal females [11] as well as playing an important role in the acquisition of peak bone mass [12]. Studies have shown that higher dietary calcium intake is associated with better BMD in adolescents [13, 14]. Few studies have looked at dietary calcium in patients on CS, especially in the younger age groups. There has only been one previous study involving Asian premenopausal SLE women looking at CS use and dietary calcium on BMD [8]. This study was conducted to ascertain the correlation between dietary calcium intake and bone mineral density in a group of Asian female premenopausal SLE patients on CS. We chose to study premenopausal women to eliminate the confounding effect of postmenopausal bone loss on BMD. The secondary aim was to see if there were any other factors influencing BMD.
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Materials and methods
BMD measurement
Patient selection
BMDs of the lumbar spine (LS; L2–L4) and hip [femoral neck (FN) and trochanter (TR)] were measured by dualenergy X-ray absorptiometry with a LUNAR DPX-IQ densitometer. The precision of the machine was 2%. The reference population used was the manufacturer’s female Japanese population database.
Premenopausal women over 18 years of age were recruited from the SLE clinic at University Malaya Medical Centre, Malaysia, from July 2002 to February 2003. All patients fulfilled the American College of Rheumatology revised criteria for the diagnosis of SLE [15]. They were ambulant, on CS, and had BMD measurements as part of an assessment for CS-induced osteoporosis. The number of daily sun hours throughout the study was constant at 11 h from sunrise to sunset. Only four patients wore headscarves; none were veiled. All patients gave verbal informed consent. Exclusion criteria Patients who were postmenopausal, had renal impairment (serum creatinine >115 μmol/l), a history of metabolic bone disorders, malabsorption and thyroid disease, or were immobilized or taking drugs which affected bone homeostasis were excluded.
Statistical analysis Statistical Package for the Social Sciences (SPSS) version 11.0 for Windows (SPSS, IL, USA) was used to perform statistical analysis. Data were expressed as mean±1SD or median. Nonparametric tests were used to analyze the relationship between dietary calcium, duration of CS use, cumulative dose of CS, mean CS dose, self-reported physical exercise, smoking, alcohol intake, and SLEDAI score with BMD. Linear regression analysis was used to determine the effect of calcium intake on BMD after allowing for CS use and exposure. A p value
