The researchers suggest that the high blood sugar that occurs in untreated diabetes damages the small blood vessels of the heart and this explains the link between diabetes and higher risk of heart attack.
Diabetes is a chronic disease that arises either because the body does not produce enough insulin (typical of type 1 diabetes) or because it cannot effectively use the insulin it produces (typical of type 2 diabetes). Around 90 percent of people with diabetes have type 2.
Insulin is a hormone that helps keep blood sugar (glucose) under control. Uncontrolled diabetes results in high blood sugar, or hyperglycemia, which, over time, damages many parts of the body, including nerves and blood vessels.
The number of people with diabetes worldwide was estimated to be 422 million in 2014, up from 108 million in 1980. The disease is a major cause of blindness, heart attack, stroke, kidney failure, and lower limb amputation
In the United States, there are now more than 29 million people with diabetes, up from 26 million in 2010.
Another 86 million people have prediabetes, a condition in which blood sugar is higher than normal but not yet in the range for type 2 diabetes.
Diabetes affects small cardiac blood vessels
Fast facts about diabetes
- The global prevalence of diabetes among adults rose from 4.7 percent in 1980 to 8.5 percent in 2014.
- Once a disease seen only in adults, the number of children with type 2 diabetes is increasing.
- The total medical costs and lost productivity and wages associated with diabetes in the U.S. came to $245 billion in 2012.
The new study - led by researchers at Technical University of Munich (TUM) in Germany - investigates the effect of diabetes on the small blood vessels, or capillaries, that surround the heart. Damage to these can affect the whole of the heart muscle.
The heart's network of veins and arteries and small offshoots into capillaries can be compared to a road traffic network. If one small minor road is blocked, it has little effect on the whole network.
However, if more and more small side roads come to a halt, the traffic on the main roads and highways becomes denser and denser, and eventually the whole system seizes up and a heart attack ensues.
The researchers suggest their findings show how diabetes can have this effect.
They compared samples of heart tissue taken from patients with and without diabetes who underwent heart transplants. The samples from patients with diabetes showed that their hearts had significantly fewer small blood vessels around them.
After running tests in the laboratory, the team also found high levels of blood sugar are linked to loss of pericytes - a type of cell that forms a protective layer around small blood vessels.
The team believes this layer stabilizes the blood vessel and causes the blood vessels to break up when damaged.
Gene therapy may reverse damage to cardiac capillaries
The researchers also studied the effect of blood vessel loss in pigs genetically engineered to develop type 1 diabetes that is like the human form. They found the same damage occurred in their hearts.
However, with the help of gene therapy, the team was able to increase production of a protein that stimulates growth of pericytes. This led to new growth of lasting and functioning small blood vessels.
It will be some time before such a treatment is available for use in humans, note the researchers, who also point out how the findings reinforce the importance of diagnosing diabetes early.
One in four people with diabetes do not know they have the disease. First author Dr. Rabea Hinkel, a cardiologist at TUM's university hospital, concludes:
"Diabetes often remains undetected in patients for years or even decades. Over that long period, massive damage can occur."