Cognitive Decline and Dementia in Some Chronic Disorders

The aim of this chapter is to review the association between cognitive impairment and four selected chronic conditions, namely, hearing loss, vitamin B12 and folate deficiencies, thyroid disease and diabetes mellitus. This chapter focuses on the prevalence, pathophysiology and the mechanistic effects of cognitive decline in these disorders. In the first section, hearing loss is discussed. In the second section, a comprehensive review covering the many aspects of vitamin B12 and folate deficiencies is presented. In the third section, thyroid disorders in relation to cognitive decline are discussed. The last section discusses diabetes mellitus and the many mechanisms through which diabetes mellitus increases the risk of cognitive impairment and dementia.