Impact of fluorosis on mineral bone disorders in CKDu populations: a cross-sectional study

Chronic kidney disease of unknown etiology (CKDu) and fluorosis are prevalent health issues in the dry zone of Sri Lanka. Mineral bone disorders (MBD) in CKDu-affected populations remain understudied, in Sri Lanka or elsewhere, creating a significant gap in knowledge. This cross-sectional study investigates MBD among CKDu patients living in fluorosis endemic regions. Ninety-six non-dialysis CKDu patients were selected. Serum calcium, phosphate, vitamin D, parathyroid hormone, as well as urinary and serum fluoride levels were measured. Bone mineral density (BMD) of the spine and femur was assessed using Dual-Energy X-ray Absorptiometry (DEXA), while plain X-rays of the pelvis/lumbar spine and forearm were obtained. To determine the prevalence of MBD in early disease, patients were classified into early and late CKDu groups based on an estimated glomerular filtration rate (eGFR) cut-off of 45 ml/min/1.73 m². A high prevalence of MBD was identified, affecting 72% of subjects, with 64.5% presenting osteopenia or osteoporosis, predominantly within the axial skeleton. Of the cases assessed, 52% exhibited at least one biochemical abnormality. 25(OH) vitamin D levels were < 20 ng/ml in 16.7% and < 30 ng/ml in 62% of total cases. All patients demonstrated elevated serum fluoride levels, averaging 1.45 ± 1.2 mg/L, significantly higher than the reference range of 0.014–0.239 mg/L observed in healthy populations from non-fluorosis endemic regions. Radiological features in favor of skeletal fluorosis were noted, including interosseous membrane calcification (14.6%) and osteosclerosis (7.3%). Logistic regression analysis adjusted for age, sex, body mass index, and biochemical markers found that bone types did not predict differences in the prevalence of bone disease between early and late stage CKDu. In Sri Lanka, mineral bone disorders of CKDu are different from typical CKD, as it resembles skeletal fluorosis with superadded effects of vitamin D insufficiency. Bone disorder risk is present even in the early stages of the disease. The study indicates that prolonged exposure to fluoride may contribute to early onset MBD in those with CKDu and highlights the need to assess fracture risk.