they help to support cognitive reserve. The neglect of these risk factors diminishes this reserve. Studies suggest that sensory impairments of vision and hearing are modifiable risk factors for dementia. These impairments may precede the cognitive symptoms of Alzheimer's disease for example, by many years. Hearing loss may lead to social isolation which negatively affects cognition. Social isolation is also identified as a modifiable risk factor. Age-related hearing loss in midlife is linked to cognitive impairment in late life, and is seen as a risk factor for the development of Alzheimer's disease and dementia. Such hearing loss may be caused by a central auditory processing disorder that makes the understanding of speech against background noise difficult. Age-related hearing loss is characterised by slowed central processing of auditory information. Worldwide, mid-life hearing loss may account for around 9% of dementia cases. Evidence suggests that frailty may increase the risk of cognitive decline, and dementia, and that the inverse also holds of cognitive impairment increasing the risk of frailty. Prevention of frailty may help to prevent cognitive decline. A 2018 review however concluded that no medications have good evidence of a preventive effect, including blood pressure medications. A 2020 review found a decrease in the risk of dementia or cognitive problems from 7.5% to 7.0% with blood pressure lowering medications. Economic disadvantage has been shown to have a strong link to higher dementia prevalence, which cannot yet be fully explained by other risk factors. Dental health Limited evidence links poor oral health to cognitive decline. However, failure to perform tooth brushing and gingival inflammation can be used as dementia risk predictors. Oral bacteria The link between Alzheimer's and gum disease is oral bacteria. In the oral cavity, bacterial species include P. gingivalis, F. nucleatum, P. intermedia, and T. forsythia. Six oral treponema spirochetes have been examined in the brains of Alzheimer's patients. Spirochetes are neurotropic in nature, meaning they act to destroy nerve tissue and create inflammation. Inflammatory pathogens are an indicator of Alzheimer's disease and bacteria related to gum disease have been found in the brains of patients with Alzheimer's disease. The bacteria invade nerve tissue in the brain, increasing the permeability of the blood–brain barrier and promoting the onset of Alzheimer's. Individuals with a plethora of tooth plaque risk cognitive decline. Poor oral hygiene can have an adverse effect on speech and nutrition, causing general and cognitive health decline. Oral