Diabetes mellitus represents a cluster of metabolic diseases characterized by high levels of blood glucose (hyperglycemia). This may be as a result of defects in insulin secretion, insulin action or both.
Insulin is a hormone secreted by beta cells of islets of langerhans, situated in pancreas. The glucagons produced by alfa cells have anti-insulin action. Both in unison keep a constant glucose level in the blood. Insulin also acts as gate keeper, where, only in its presence can the blood glucose enter the body cells and provide fuel and energy to work.
In diabetes, the cellular fuel is thus compromised, while excess of glucose remains in the circulation.

Yoga Related Observations:
Regular practice of yoga does reduce blood sugar levels, the blood pressure, weight, the rate of progression to the complications, and the severity of the complications as well.
The symptoms are also reduced to a great extent, so are number of diabetes related hospital admissions. The quality of life questionnaires do reveal a remarkable improvement in the scores. These finding are uniform for all those who are trying to find effect of yoga on diabetes.

How Yoga works? (Possible mechanisms)
1. Glucagons secretion is enhanced by stress. Yoga effectively reduces stress, thus reducing glucagons and possibly improving insulin action.
2. Weight loss induced by yoga is a well accepted mechanism.
3. Muscular relaxation, development and improved blood supply to muscles might enhance insulin receptor expression on muscles causing increased glucose uptake by muscles and thus reducing blood sugar.
4. Blood pressure plays a great role in development of diabetic and related complications, which is proven to be benefited by yoga. The same holds true for increased cholesterol levels.
5. Yoga reduces adrenaline, noradrenalin and cortisol in blood, which are termed as ‘stress hormones’. This is a likely mechanism of improvement in insulin action.
6. Many yogic postures do produce stretch on the pancreas, which is likely to stimulate the pancreatic function.

In India, we are having many patients controlled only on so called ‘lifestyle modification’ i.e. yoga essentially.
We are also trying to recruit many ‘impaired glucose tolerance’ patients
(Pre-diabetic patients, as suggested by clinical and laboratory evaluations) in our ‘Prevention of Diabetes – Yoga Way Programme’ (PDYW).
We accept that our work is going very slowly due to lack of funds, but we are certain that we will stun the world soon with our results. Source