Primary antiphospholipid syndrome in premenopausal women: low vitamin D, high fat mass and maintained bone mineral mass

The aim of this study was to analyze vitamin D levels and their association with bone mineral density and body composition in primary antiphospholipid syndrome. For this cross-sectional study 23 premenopausal women with primary antiphospholipid syndrome (Sapporo criteria) and 23 age- and race-matched healthy controls were enrolled. Demographic, anthropometric, clinical and laboratorial data were collected using clinical interview and chart review. Serum 25-hydroxyvitamin D levels, parathormone, calcium and 24-hour urinary calcium were evaluated in all subjects. Bone mineral density and body composition were studied by dual X-ray absorptiometry. The mean age of patients and controls was 33 years. Weight (75.61 [20.73] vs. 63.14 [7.34] kg, p = 0.009), body mass index (29.57 [7.17] vs. 25.35 [3.37] kg, p = 0.014) and caloric ingestion (2493 [1005.6] vs. 1990 [384.1] kcal/day, p = 0.03) were higher in PAPS than controls. All PAPS were under oral anticoagulant with INR within therapeutic range. Interestingly, biochemical bone parameters revealed lower levels of 25-hydroxyvitamin D [21.64 (11.26) vs. 28.59 (10.67) mg/dl, p = 0.039], serum calcium [9.04 (0.46) vs. 9.3 (0.46) mg/dl, p = 0.013] and 24-hour urinary calcium [106.55 (83.71) vs. 172.92 (119.05) mg/d, p = 0.027] in patients than in controls. Supporting these findings, parathormone levels were higher in primary antiphospholipid syndrome than in controls [64.82 (37.83) vs. 44.53 (19.62) pg/ml, p = 0.028]. The analysis of osteoporosis risk factors revealed that the two groups were comparable (p > 0.05). Lumbar spine, femoral neck, total femur and whole body bone mineral density were similar in both groups (p > 0.05). Higher fat mass [28.51 (12.93) vs. 20.01 (4.68) kg, p = 0.005] and higher percentage of fat [36.08 (7.37) vs. 31.23 (4.64)%, p = 0.010] were observed in PAPS in comparison with controls; although no difference was seen regarding lean mass. In summary, low vitamin D in primary antiphospholipid syndrome could be secondary to higher weight and fat mass herein observed most likely due to adipocyte sequestration. This weight gain may also justify the maintenance of bone mineral density even with altered biochemical bone parameters.