Osteoclast constraint in trabecular remodeling

We previously reported lower fracture rates in our rural population [1]. BMD did not differ (femoral neck BMD, p=0.56) although rural residents reported lower prevalence of arthritis (p=0.006) and serum vitamin D was 8% higher (p=0.16). Fall frequency and characteristics may be protective but falls ascertainment is often suboptimal, relying on lengthy recall in elderly people. This analysis investigates whether falls risk differs between urban and rural participants using standardised, monthly falls ascertainment. The current analysis is part of a RCT, due for completion in 2008, to investigate whether an annual dose of vitamin D (500,000 IU cholecalciferol) reduces falls and fractures compared with placebo in women aged N70 year. Falls were ascertained from June 2003 to October 2006 providing 3889 person-years follow-up (median 13 months, range: 1–40). The median age of participants in both groups is 76 years (range: 70–93). Baseline serum vitamin D and PTH levels were measured in a subset of 30 rural and 81 urban participants. A higher proportion of rural participants have fallen (rural vs. urban: n=395/649 (61%) vs. n=549/1004 (55%), respectively; p=0.013). Of the fallers, ninety-one women sustained a fracture (rural 33/394 (8.4%) vs. urban 58/546 (10.6%)). There was a trend showing rural women were less likely to sustain a fracture in the fall (OR (95% CI): 0.77 (0.49, 1.20), p=0.247). Baseline serum vitamin D was 17% higher and PTH 16% lower in rural participants (rural vs. urban: vitamin D: 58.5±20.3 vs. 49.8± 13.8 nmol/l; lnPTH 1.34±0.48 and 1.59±0.49; p=0.016). The results support the higher falls rate reported in rural Poland [2]. The higher baseline vitamin D data suggest it may be protective of falls-related injury. The data are consistent with a proposed role of vitamin D in ‘fast twitch’ muscle fibres helping to ‘save’ oneself during a fall. Since 90% of hip fractures result from a fall, the reliable falls ascertainment and characterisation could facilitate development of effective and economical preventative strategies, including high dose annual vitamin D supplementation.