Diabetes mellitus is a complex metabolic disorder with multifactorial etiology, such as complex interaction of genetics and environmental factors, which affect different organs of the body. The symptoms of diabetes or clinical features have three cardinal manifestations:

1. Polydypsia – excessive thirst.
2. Polyuria      - excessive production and passing of urine.
3. Polyphagia – excessive hunger.

Other than these three cardinal manifestations, diabetes also have other symptoms, some of which are due to diabetes itself and some of the diabetes symptoms are due to other related diseases which may be associated with diabetes.

Diabetes symptoms (mainly due to hyperglycemia) also include weight loss (generally due to urinary loss of glucose and calories, muscle breakdown and protein degradation and decreased protein synthesis, all of which are effects of catabolic state), fatigue, weakness, blurring of vision (may be due to diabetic complication of eye or due to changes in the water content of the lens, but generally resolves as the hyperglycemia is controlled), frequent superficial infections (vaginitis, fungal skin infections etc.), and slow healing of skin lesions even after minor trauma/injury.

Symptoms of Type-1 Diabetes:

Other than the three cardinal manifestations, type-1 diabetes has some other symptoms. The age at which type-1 diabetes generally occurs is below 20 years (accounts for 80% of cases of type-1 diabetes). Obesity may be associated with type-1 diabetes in approximately 25% of cases. Acanthosis nigricans (a type of hyper-pigmentation of skin) is present in less than 2% of the type I diabetes patients. Hypertension is also a very rare coincidence in type I diabetic patients. The concordance of type-1 diabetes in identical twins is between 30% and 70%.

Ketoacidosis is more common in type-1 diabetes. There is an increased risk of autoimmune disorders in type-1 diabetes, such as autoimmune thyroid disease, adrenal insufficiency, pernicious anemia, celiac disease, and vitiligo.

Symptoms of Type-2 Diabetes:

Type-2 diabetes has symptoms other than the three cardinal manifestations, namely polyuria, polyphagia and polydypsia. Type-2 diabetes generally occurs later in life and most are after the age of 40 years. The rate for concordance for type 2 diabetes in monozygotic twins is about 80% (range from 70% to 90%).

Obesity is very common among individuals with type-2 diabetes and almost all patients (young as well as adults) with type-2 diabetes are obese. Acanthosis nigricans is present in 60-80% of the patients with type-2 diabetes, in compare to less than 2% in type-1 diabetes. Approximately 30% of individuals with type-2 diabetes have hypertension (high blood pressure).

Ketoacidosis is less common in type-2 diabetes.