It develops slowly, and because there are rarely any apparent symptoms, it can often go undiagnosed until a bone is broken.
In the United States, osteoporosis affects about 10 million people.
Over recent decades, a number of studies have looked for potential links between osteoporosis and dementia.
Recently, researchers from the Epidemiology Team of IQVIA — a healthcare data science company based in Frankfurt, Germany — set out to explore the relationship between these seemingly disparate conditions.
They used data from the Disease Analyzer database, which compiles information about diagnoses, prescriptions, and demographic information taken from computer systems used by doctors.
Their findings were published last month in the Journal of Alzheimer's Disease.
Dementia risk and osteoporosis
The study included almost 60,000 matched participants: 29,983 individuals with osteoporosis and the same number of controls without osteoporosis.
Participants were matched by a number of variables, including age, sex, other medical conditions that they had, and medications that they were taking. They were followed for up to 20 years.
"There is big interest in the relationship between osteoporosis and dementia. This study is the first to address this question in a very large database enabling the case-control-comparison between patients with and without osteoporosis."
Lead investigator Prof. Karel Kostev
By the end of the study, 20.5 percent of the women with osteoporosis and 16.4 percent of controls had been diagnosed with dementia. In men, dementia was diagnosed in 22 percent of those with osteoporosis and 14.9 percent of men without osteoporosis.
Breaking it down, that equates to a 1.2-fold increase in dementia risk for women and a 1.3-fold increase for men.
Why does dementia risk increase?
While there is no definitive answer to this question, there are some theories. As co-author Dr. Louis Jacob explains, "The major hypothesis to explain the association between osteoporosis and dementia is that these two conditions have similar risk factors."
There are a collection of biomarkers that are found in both conditions.
For instance, ApoE4 increases the risk of both dementia and osteoporosis. Similarly, lower levels of vitamin K, vitamin D, androgens (such as testosterone), and estrogens also raise the risk of both conditions.
Because the study used such a large dataset, the findings are robust. However, the scientists also note some shortcomings. For instance, they did not have full access to lifestyle factors that could have played a role in disease progression, such as alcohol consumption, physical activity, and smoking status.
For those who have osteoporosis or know someone who has, it is worth putting the risk increases into perspective. In the United States, roughly 9 out of every 100 people over the age of 65 have dementia.
If we raise this risk 1.3-fold for men with osteoporosis, it equates to around 12 people in every 100 — an extra 3 cases of dementia per 100 people with osteoporosis.
However, at population level, a 1.2- or 1.3-fold increase becomes much more important. Worldwide, for instance, osteoporosis affects an estimated 200 million women. In this case, a 1.2-fold increase in dementia risk could account for millions of additional cases of dementia.
The researchers hope that their findings will help scientists delve into the mechanisms shared by both conditions, potentially providing insight into the treatment and prevention of dementia and osteoporosis.