Diabetes
Diabetes mellitus, commonly known as diabetes, is a group of common endocrine diseases characterized by sustained high blood sugar levels. Diabetes tends to progress in severity, and is due to either a reduced production of the hormone insulin by the pancreas or unresponsiveness of bodily cells to insulin's effects. Classic symptoms include the three Ps: polydipsia, polyuria, and polyphagia, together with weight loss and blurred vision. If left untreated, the disease can lead to many health complications, including disorders of the cardiovascular system, eye, kidney, and nerves.
The major types of diabetes are type 1 and type 2. The most common type is type 2. The most common treatment for type 1 is insulin replacement therapy, while anti-diabetic medications and lifestyle modifications can be used to manage type 2. Gestational diabetes, a form that sometimes arises during pregnancy, normally resolves shortly after delivery. Type 1 diabetes is an autoimmune condition in which the body's immune system attacks the beta cells in the pancreas, preventing the production of insulin. This condition typically is present from birth or develops early in life. Type 2 diabetes occurs when the body becomes resistant to insulin, meaning the cells do not respond effectively to it, and thus, glucose remains in the bloodstream instead of being absorbed by the cells. Additionally, diabetes can result from other specific causes, such as genetic conditions, diseases affecting the pancreas, or the use of certain medications and chemicals.
The number of people worldwide diagnosed as living with diabetes has increased sharply in recent decades, from 200 million in 1990 to 828 million in 2024. Diabetes accounts for some two million deaths each year, and more than half of those affected are unaware of their condition. It affects one in seven of the adult human population, with type 2 diabetes accounting for more than 95% of cases. These numbers have already risen beyond earlier projections of 783 million adults by 2045. The prevalence of the disease continues to increase, most dramatically in low-middle income nations, where it is now the seventh leading cause of death. Rates are similar in women and men. The global expenditure on diabetes-related healthcare is an estimated US$760 billion a year.
Signs and symptoms
Common symptoms of diabetes include increased thirst, frequent urination, extreme hunger, and unintended weight loss. Several other non-specific signs and symptoms may also occur, including fatigue, blurred vision, sweet smelling urine/semen and genital itchiness due to Candida infection. About half of affected individuals may also be asymptomatic. Type 1 presents abruptly following a pre-clinical phase, while type 2 has a more insidious onset; patients may remain asymptomatic for many years.Diabetic ketoacidosis is a medical emergency that occurs most commonly in type 1, but may also occur in type 2 if it has been longstanding or if the individual has significant β-cell dysfunction. Excessive production of ketone bodies leads to signs and symptoms including nausea, vomiting, abdominal pain, the smell of acetone in the breath, deep breathing known as Kussmaul breathing, and in severe cases decreased level of consciousness. Hyperosmolar hyperglycemic state is another emergency characterized by dehydration secondary to severe hyperglycemia, with resultant hypernatremia leading to an altered mental state and possibly coma.
Hypoglycemia is a recognized complication of insulin treatment used in diabetes. An acute presentation can include mild symptoms such as sweating, trembling, and palpitations, to more serious effects including impaired cognition, confusion, seizures, coma, and rarely death. Recurrent hypoglycemic episodes may lower the glycemic threshold at which symptoms occur, meaning mild symptoms may not appear before cognitive deterioration begins to occur.
Long-term complications
The major long-term complications of diabetes relate to damage to blood vessels at both macrovascular and microvascular levels. Diabetes doubles the risk of cardiovascular disease, and about 75% of deaths in people with diabetes are due to coronary artery disease. Other macrovascular morbidities include stroke and peripheral artery disease.Microvascular disease affects the eyes, kidneys, and nerves. Damage to the retina, known as diabetic retinopathy, is the most common cause of blindness in people of working age. The eyes can also be affected in other ways, including development of cataract and glaucoma. It is recommended that people with diabetes visit an optometrist or ophthalmologist once a year.
Diabetic nephropathy is a major cause of chronic kidney disease, accounting for over 50% of patients on dialysis in the United States. Diabetic neuropathy, damage to nerves, manifests in various ways, including sensory loss, neuropathic pain, and autonomic dysfunction. Loss of pain sensation predisposes to trauma that can lead to diabetic foot problems, the most common cause of non-traumatic lower-limb amputation.
Hearing loss is another long-term complication associated with diabetes.
Based on extensive data and numerous cases of gallstone disease, it appears that a causal link might exist between type 2 diabetes and gallstones. People with diabetes are at a higher risk of developing gallstones compared to those without diabetes.
There is a link between cognitive deficit and diabetes; studies have shown that diabetic individuals are at a greater risk of cognitive decline, and have a greater rate of decline compared to those without the disease. Diabetes increases the risk of dementia, and the earlier that one is diagnosed with diabetes, the higher the risk becomes. The condition also predisposes to falls in the elderly, especially those treated with insulin.
Types
Diabetes is classified by the World Health Organization into six categories:- Type 1 diabetes
- Type 2 diabetes
- Hybrid forms of diabetes
- Hyperglycemia first detected during pregnancy
- Other specific types
- Unclassified diabetes
Type 1
Type 1 accounts for 5 to 10% of diabetes cases and is the most common type of diabetes diagnosed in patients under 20 years; however, the older term "juvenile-onset diabetes" is no longer used as onset in adulthood is possible. The disease is characterized by loss of the insulin-producing beta cells of the pancreatic islets, leading to severe insulin deficiency, and can be further classified as immune-mediated or idiopathic. The majority of cases are immune-mediated, in which a T cell-mediated autoimmune attack causes loss of beta cells and thus insulin deficiency. Patients often have irregular and unpredictable blood sugar levels due to very low insulin and an impaired counter-response to hypoglycemia.Type 1 diabetes is partly inherited, with multiple genes, including certain HLA genotypes, known to influence the risk of diabetes. In genetically susceptible people, the onset of diabetes can be triggered by one or more environmental factors, such as a viral infection or diet. Several viruses have been implicated, but to date there is no stringent evidence to support this hypothesis in humans.
The genes that are responsible for diabetes are still being researched, but scientists have narrowed them down by investigating the gene mutations related to the capability of the body’s β-cells to produce insulin. Genes related to environmental responses also contribute to a person’s amount of genetic risk for diabetes. The occurrence of diabetes in monozygotic and dizygotic twins has been tested, and these rates can give insight into the genetic component of diabetes. In type 1 diabetes, the chance of monozygotic twins both developing the disease was greater than the risk for dizygotic twins. However, the rate of any siblings contracting the disease was much greater with type 2 diabetes. This indicates that there must be a large environmental factor involved in type 2, and some genetic factor with type 1. It must be noted, also, that type 1 diabetes has only about a 50% concordance rate. So, it is not fully genetic, but the results from the twin studies point to some inherited risk.
Type 1 diabetes can occur at any age, and a significant proportion is diagnosed during adulthood. Latent autoimmune diabetes of adults is the diagnostic term applied when type 1 diabetes develops in adults; it has a slower onset than the same condition in children. Given this difference, some use the unofficial term "type 1.5 diabetes" for this condition. Adults with LADA are frequently initially misdiagnosed as having type 2 diabetes, based on age rather than a cause. LADA leaves adults with higher levels of insulin production than type 1 diabetes, but not enough insulin production for healthy blood sugar levels.
Type 2
Type 2 diabetes is characterized by insulin resistance, which may be combined with relatively reduced insulin secretion. The defective responsiveness of body tissues to insulin is believed to involve the insulin receptor. However, the specific defects are not known. Diabetes mellitus cases due to a known defect are classified separately. Type 2 diabetes is the most common type of diabetes mellitus accounting for 95% of diabetes. Many people with type 2 diabetes have evidence of prediabetes before meeting the criteria for type 2 diabetes. The progression of prediabetes to overt type 2 diabetes can be slowed or reversed by lifestyle changes or medications that improve insulin sensitivity or reduce the liver's glucose production.Type 2 diabetes is primarily due to lifestyle factors and genetics. A number of lifestyle factors are known to be important to the development of type 2 diabetes, including obesity, lack of physical activity, poor diet such as Western Pattern Diet, and stress. Excess body fat is associated with 30% of cases in people of Chinese and Japanese descent, 60–80% of cases in those of European and African descent, and 100% of Pima Indians and Pacific Islanders. Even those who are not obese may have a high waist–hip ratio.
Dietary factors such as sugar-sweetened drinks are associated with an increased risk. The type of fats in the diet is also important, with saturated fat and trans fats increasing the risk and polyunsaturated and monounsaturated fat decreasing the risk. Eating white rice excessively may increase the risk of diabetes, especially in Chinese and Japanese people.
Adverse childhood experiences, including abuse, neglect, and household difficulties, increase the likelihood of type 2 diabetes later in life by 32%, with neglect having the strongest effect.
Antipsychotic medication, SSRI, and SNRI side effects are also potential risk factors.