Osteoporosis and Alzheimer's disease (AD) are the two common diseases mostly 
affecting persons aged over 60. Epidemiological findings revealed that 
osteoporosis and AD have a very high comorbidity. However, the mechanisms 
underlying their association are poorly understood. The Wnt signaling pathway 
plays a crucial role in the proper development and maintenance of brain and bone 
structure and function. Dickkopf-related protein 1 (Dkk1), a vital antagonist of 
the Wnt signaling, was reported to be closely associated with bone homeostasis 
and osteoporosis. Interestingly, high level of Dkk1 in the brain increases the 
risk of AD. It is suggested that Dkk1 may be a common potent risk factor 
involved in osteoporosis and AD. Therefore, we hypothesize that Dkk1 may play a 
role in both osteoporosis and AD. Our hypothesis will shed new light on the 
understanding of the relationship between these two diseases and help to explain 
some common characters of osteoporosis and AD.