Walking ≥10,000 Steps per Day is not Associated with Higher Bone Density in Women Across the Lifespan

Abstract

Pedometers have become increasingly popular for use in research and among the general public to promote physical activity and health. Accumulation of ∼10,000 steps/ day has been associated with improved body composition, lower blood pressure and improved lipid profiles and glucose tolerance. PURPOSE: To evaluate the impact of habitually walking ≥10,000 steps/day on bone mineral density (BMD) in women across the lifespan. METHODS: Dual X-ray absorptiometry scans of the whole body (WB), proximal femur (PF), femoral neck (FN), and lumbar spine (LS) were performed on 104 pre- and postmenopausal women (47.1±20.0 years) to obtain measures of bone mineral content, BMD, lean soft tissue (LST), and fat mass (FM). Physical activity (steps/day) was assessed from 7-day pedometer counts. RESULTS: Walking ≥10,000 steps/day did not result in better WB, PF, FN or LS BMD than walking <10,000 steps/day (p >0.05). When the sample was split on the step categories suggested by Tudor-Locke & Basset (2004), women walking ≥10,000 steps/day had higher WB BMD (1.118±0.017 g.cm−2) compared to women who averaged <5000 steps/day (1.005±0.044 g.cm−2, p = 0.017) and a higher FN BMD (0.822±0.148 g.cm−2) than women who walked <5000 (0.710±0.133 g.cm−2, p = 0.038) or 5000-7499 (0.743±0.120 g.cm−2, p = 0.035) steps/day. Adjusting for age, FM and LST rendered these differences non-significant (p >0.05). Similarly, grouping the sample into quartiles of physical activity, the women in the highest quartile (12,782-20,504 steps/day) had higher PF (0.983±0.155 g.cm−2) and FN (0.882±0.161 g.cm−2) BMD compared to women in the lowest (0.871±0.124, 0.736±0.129 g.cm−2), 2nd (0.910±0.121, 0.775±0.119 g.cm−2), and 3rd (0.897±0.119, 0.771±0.143 g.cm−2) quartiles (all p <0.05). Women in the highest quartile also had higher WB BMD (1.152±0.021 g.cm−2) compared to women of the lowest 2 quartiles (1.066±0.120, 1.074±0.083 g.cm−2) and higher LS BMD (1.045±0.163 g.cm−2) compared to women in the 3rd quartile (0.967±0.148 g.cm−2) (all p <0.05); however, adjusting for age, FM, and LST, abolished these differences (p >0.05). CONCLUSIONS: Walking up to ∼13,000 steps/day may not be enough stimulus to impact bone health in women across the lifespan or the complex interactions between age, physical activity and LST and FM may obscure physical activity effects.