Physical and cognitive changes occur in late adulthood. Life expectancy has increased to around 80 years due to advances in medicine. Physical changes include presbycusis (age-related hearing loss), declining senses of smell and taste, osteoporosis, sleep issues, and sexual changes like diminished libido. Cognitive theories of aging include the cellular clock theory, hormonal stress theory, and free radical theory. Common health concerns in late adulthood are heart disease, cancer, stroke, arthritis, accidents, dementia and Alzheimer's disease. Memory involves both retrospective memories of the past and prospective memories of future plans.