The blood sugar level is simply the amount of glucose in the blood, and people with high levels can be below the level that would indicate diabetes and still be at an increased risk for cardiovascular disease.
"A lot of people are dying as a result of their blood glucose being elevated even though many may well be below the clinical threshold of what we call diabetes," Dr Majid Ezzati, of the Harvard School of Public Health in Boston.
The research -- published in The Lancet -- is based on analysis of high glucose levels and their impact on 2001 deaths from heart disease and strokes in 52 countries. High blood sugar was linked to 3.1 million deaths, more than 2.4 million of which were caused by being overweight or obese. Fewer than 4.8 million deaths were attributed to smoking, and 3.9 million were caused by high cholesterol.
"Even people who are in pre-diabetes level have blood glucose levels that from a cardiovascular perspective has some risk associated with it," said Ezzati. "The small risks are accumulating and causing a lot of deaths even though they don't fall into any clinical classification."
"This study explains why high-fructose corn syrup, white flour, sugar and other refined carbohydrates are so dangerous to human health," said Mike Adams, author of "How to Halt Diabetes in 25 Days." "Consuming these ingredients elevates blood sugar levels, and high blood sugar is clearly linked to heart attacks and strokes."