Diabetes has been linked to earlier onset of dementia and Alzheimer's, and leaving the illness untreated or unchecked may lead to the progression of other diseases and changes in behavior, as well as emotions.

A recent study reveals that mid-life diabetes contributes to an accelerated aging process by five years. People with diabetics experience decline in mental performance compared to people with normal blood sugar.

Researchers from the Johns Hopkins University saw the advancement of aging among diabetics after they had evaluated data of 15,800 middle-aged adults in the United States from the Atherosclerosis Risk in Communities Study (ARIC).

The research group analyzed and assessed the participants' cognitive function during three of the five periodic visits during the study period. The study began in 1987 and ended in 2013.

The participants' average age was  57 years old when they entered the study. About a quarter were black, and about 13 per cent had diabetes.

The researchers discovered a 19 per cent rise in the mental decline among those participants with unmanaged or undercontrolled diabetes, while those with controlled diabetes and pre-diabetes suffered smaller declines in mental capabilities.

"There is a substantial cognitive decline associated with diabetes, pre-diabetes and poor glucose control in people with diabetes. The lesson to learn is that for a healthy brain you need to eat right when you're 70 and exercise when you're 50," according to Elizabeth Selvin, study lead author and associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health.

Those without diabetes but with high blood sugar at that first visit also experienced cognitive decline during the study period, compared to those with better blood sugar control.

The findings suggest that people who control their blood sugar early in life may also protect their brain's health. However, this claim needs to be substantiated by more studies, the researchers said.

"It gives you an enormous window of opportunity for prevention," said coauthor Dr. A. Richey Sharrett. "After all, I think people dread dementia more than they dread anything in old age."

Known as a silent killer, Diabetes occurs when the body fails to produce insulin for glucose control. This eventually leads to elevated levels of sugar in the blood, which affects the vascular system of the body and may cause various diseases, including nerve damage, blindness and kidney disease, as well as instability in one's emotions that usually leads to depression and impulsive behavior.

The study was published in the journal Annals of Internal Medicine.