Osteoporosis is more prevalent in older women than in older men, for reasons related to estrogen deficiency, but the detailed mechanisms remain less clear than clinicians would like them to be. Many aspects of aging are correlated with one another. Aging is a burden of damage and consequences of that damage, progressing at modestly different paces in different individuals, largely due to variations in lifestyle choices and environmental exposure to persistent pathogens. Genetics plays some role, but probably only a small role in near all people. Thus more damage gives rise to a greater risk of many different age-related conditions in the same individual. Still, in some cases, one condition can contribute directly to another. For example, to the extent that osteoporosis restricts activity (and thus vascular health, cerebral blood flow, and so forth), it will likely harm cognitive health over time.
Dementia and osteoporosis are highly prevalent in the elderly population and often coexist. Individuals with dementia are at high risk of osteoporosis and hip fracture. It has been estimated that approximately 40% of patients with hip fracture have a prior diagnosis of dementia. The risk of hip fracture in Alzheimer's disease was recently reported in a meta-analysis of nine cohorts from the United States, Canada, and the UK to be over twofold compared to those without dementia. Furthermore, this study also demonstrated that hip bone mineral density (BMD) was lower in those affected compared to controls.
Notably, a recent study has demonstrated increased risk of dementia following both hip and non-hip fractures. Although the risk of dementia was highest following hip fracture (60%), vertebral (47%), lower (35%), and upper limb (29%) fractures were also associated with increased risk. These findings are particularly important as non-hip fractures are very common, affecting two in five women and one in three men after the age of 60 years.
The nature of the association between osteoporosis and dementia is not entirely clear. Most authors to date believe that the association between these two common conditions is likely driven by common risk factors such as old age, sedentary lifestyle, physical decline, vitamin D insufficiency, sarcopenia, and propensity to falls. However, there is some evidence that suggests that hip fracture per se may lead to complications which directly precipitate dementia development. Furthermore, at least two studies have shown a significant association between low BMD or bone loss and subsequent cognitive decline in postmenopausal women. However, studies investigating the longitudinal long-term association between cognitive decline and both bone loss and fracture risk are lacking.
This study aimed to determine the association between: (i) cognitive decline and bone loss; and (ii) clinically significant cognitive decline on Mini Mental State Examination (MMSE) over the first 5 years and subsequent fracture risk over the following 10 years. A total of 1741 women and 620 men aged ≥65 years from the population-based Canadian Multicentre Osteoporosis Study were followed from 1997 to 2013. Over 95% of participants had normal cognition at baseline. After multivariable adjustment, cognitive decline was associated with bone loss in women but not men. Approximately 13% of participants experienced significant cognitive decline by year 5. In women, fracture risk was increased significantly. There were too few men to analyze. There was a significant association between cognitive decline and both bone loss and fracture risk, independent of aging, in women