Insomnia has been defined as a difficulty initiating or maintaining sleep, leading to sleep that is either insufficient or unrefreshing. It is well-established that insomnia is more common in people with dementia, but it is not clear if insomnia predates dementia in these individuals. This latter question is an important one: if it can be shown that people with insomnia are more likely to develop dementia in later life, this may improve our ability to predict an individual's dementia risk, and possibly to help manage that risk. Several recent studies have found a link between insomnia and later dementia, but typically give little information about the time between the onset of insomnia and the onset of dementia, raising the possibility that the insomnia is an early symptom of dementia, rather than a risk factor or potential cause of the disease. Furthermore, in some studies the link between insomnia and dementia becomes weaker when factors such as depression and sleeping tablet use are taken into account. The proposed study uses primary care records to learn whether people with dementia are more likely to have consulted with their general practitioner (GP) about insomnia 5-10 years earlier, compared to those who do not have dementia.
We propose a 1:1 matched case-control study, using 8414 anonymised GP records already acquired for our main study (ISAC Protocol 15_111R). The study aims to explore the association between insomnia and later dementia. Insomnia consultations will be identified using relevant Read codes. Our measure of insomnia will be the the number of months in which the patient consulted the GP about insomnia, during the period 5-10 years before the index date (defined for cases as the first coded diagnosis of dementia). This 5-10 year exposure window will help address the problem of 'reverse causality', whereby we might record insomnia episodes which are merely an early symptom of dementia, rather than a risk factor for later disease. We will use conditional logistical regression to estimate the odds ratio (OR) of developing dementia in those exposed compared to those not exposed, and to control for covariates including benzodiazepine and z-drug use, mental and physical health comorbidities, and GP visit frequency.
Dementia diagnosis.
Elizabeth Ford - Chief Investigator - Brighton and Sussex Medical School
Richard Hoile - Corresponding Applicant - Sussex Partnership NHS Foundation Trust
Helen Smith - Collaborator - Nanyang Technological University
Jackie Cassell - Collaborator - Brighton and Sussex Medical School
Naji Tabet - Collaborator - Brighton and Sussex Medical School
Philip Rooney - Collaborator - University of Sussex
Stephen Bremner - Collaborator - Brighton and Sussex Medical School