Читать книгу Pathy's Principles and Practice of Geriatric Medicine - Группа авторов - Страница 178

A wealth of animal and human data provide evidence for a relationship between physical activity and bone health at all ages. Mechanical loading of the skeleton generally leads to favourable site‐specific changes in bone density, morphology, or strength, whereas unloading (in the form of bed rest, immobilisation, casting, spinal cord injury, or space travel) produces rapid and sometimes dramatic resorption of bone, increased biochemical markers of bone turnover, changes in morphology such as increased osteoclast surfaces, and increased susceptibility to fracture.

Comparative studies of athletic and non‐athletic populations usually demonstrate significantly higher bone density in the active cohorts, ranging from 5 to 30% higher, depending on the type, intensity, and duration of exercise training undertaken and the characteristics of the athletes studied. Exceptions occur with non‐weight‐bearing activities such as swimming, cycling, or amenorrhoeic or competitive distance runners, whose bone density appears similar to or lower than that of controls. Similarly, on a smaller scale, differences are often observed between habitually active and sedentary non‐athletic individuals. Experimental evidence in animal models and also some human data suggest that changes in bone strength not directly correlated with density may contribute to the overall benefits of mechanical loading for skeletal integrity and resistance to fracture (e.g., increased bone volume or altered trabecular morphology) so that evaluating bone density changes alone likely significantly underestimates the skeletal benefits of loading.

Consistent with the bone density findings noted above, hip fracture incidence has been observed to be as much as 30–50% lower in older adults with a history of higher levels of physical activity in daily life, compared with age‐matched, less active individuals. For example, in the prospective Epidemiology of Osteoporosis Study (EPIDOS) study of 6901 white women over the age of 75 followed for 3.6 years, investigators found that a low level of physical activity increased the risk for proximal humerus fracture by more than twofold. The relative risk of fracture in sedentary women (RR = 2.2) was greater than that attributable to low bone density (RR = 1.4), maternal history of hip fracture (RR = 1.8), or impaired balance (RR = 1.8). The interaction of these risk factors is indicated by the fracture rate, which rose from about 5 per 1000 woman‐years in individuals with either bone fragility or high fall risk to 12 per 1000 woman‐years for women with both types of risk factors. Such data suggest the great potential utility of multifactorial prevention programmes for osteoporotic fracture that can address both bone density and fall risk (sedentary behaviour, sarcopenia, poor balance, polypharmacy, etc.) simultaneously.