I. Introduction
According to the World Health Organization (WHO), dementia is among the main causes for disability and dependency of elderly people worldwide [1]. The western biomedical perception of dementia defines it as clinical syndrome. It is characterized as an occurrence of symptoms, which can be linked to the impairment in cognitive functions e.g. memory, learning capacity or language and their steady decline that cannot be traced back to normal age-related restrictions. These symptoms are often accompanied or preceded by a lack of motivation, decreasing emotional control and altered social behaviour [2]. But there are not only physical, psychological or social implications. Due to medical costs and care also economic consequences should be considered [1]. In 2016, 47 million people worldwide suffered from dementia, which causes $ 818 billions of costs in total and will become a trillion-dollar disease by 2018. The number of people suffering from dementia is estimated to increase up to 131 million by 2050 [3]. It is assumed that 94 % of people with dementia in low-and middle-income countries are cared for at home because the cost of care in a nursing home is too high or the health care systems offer insufficient support for people with dementia and their families [4]. As the most significant problem and reason for the placement of dependent persons in nursing homes, caregivers report sleep disruptions. People with dementia can have sleep disturbance up to a change of the day-night rhythm, which also affects caregivers and their environment. Also, 40 % of injuries occuring at night time are reported as a result of night falls [5]. The association of dementia with the disturbance of circadian rhythms like rest or activity cycles has been documented by several studies, too [6]–[10].