Old habits die hard: evidence of osteomalacia in two Dominican cloistered nuns from the monastery of Santa Catalina de Siena (Cuenca, Spain)

Abstract Osteomalacia remains rarely identified in paleopathology despite its characteristic skeletal manifestations. Cloistered religious communities constitute a high-risk context as older age, extensive body covering, indoor confinement, and periodic fasting collectively reduce cutaneous vitamin D synthesis and dietary intake. This study presents the skeletal remains of two nuns recovered from the Dominican convent of Santa Catalina de Siena in Belmonte (Cuenca, Spain), dating respectively to the 16th-18th and 19th-20th centuries, and evaluates skeletal macro- and micro-topographic structure consistent with osteomalacia. Individual Sk.#23 (40–59 years) exhibits pseudofractures in typical locations (costal transverse processes, scapular spine, ribs), femoral neck non-union, and coxa vara deformity. Individual Sk.#2413 (> 60 years) presents an actively remodeling scapular lesion with disorganized callus formation and distal ulnar proliferation, both suggestive of metabolic bone weakness, although diagnostic certainty is limited by incomplete preservation. Scanning Electron Microscopy (SEM) and X-Ray Fluorescence spectroscopy (XRF) analysis of a rib pseudofracture from Sk.#23 reveal porous, disorganized callus topography and reduced mineral content, supporting defective osteoid mineralization. Although genetic forms of osteomalacia were not discarded, the cloistered lifestyle supports a dietary mediated rather than hereditary etiology. These findings expand the documented temporal and geographic range of osteomalacia in European monastic settings and underscore the value of integrating macroscopic, microstructural, and compositional analysis for diagnosing metabolic bone disease in archaeological remains.