Complex connection

Two of the most worrisome trends in healthcare — the soaring rates of Type 2 diabetes and dementia — have biological factors in common. And scientists are beginning to think that is more than just a coincidence. In fact, many now believe that proper control of blood sugar could pay dividends in the future by reducing the number of people stricken by Alzheimer's disease, other forms of dementia and even the normal cognitive decline that comes with age. The key characteristics found in heart disease and stroke — clogged arteries and inflammation in cells — also affect the brain, says Debra Cherry, executive vice-president of the Alzheimer's Association, California Southland chapter. "What is good for the reduction of diabetes risk is also good for reduction of the risk of cognitive impairment," she says. About 6.8 million people in the US have some type of dementia. Alzheimer's disease is the most common, affecting 5.4 million people, according to the Alzheimer's Association. The cause is unknown and there are no treatments to slow the disease process. More than 8 per cent of American adults and children have either Type 1 or Type 2 diabetes, a number that is expected to grow in step with the rise in rates of obesity. Diabetes is diagnosed when the body can't produce enough insulin or use insulin properly to remove sugar from the bloodstream. When blood sugar remains too high, it can even lead to heart disease and other health problems. Type 1 diabetes is usually diagnosed in childhood and requires insulin, while Type 2 involves weight gain in adulthood. The relationship between diabetes and dementia drew headlines last September when a study in Japan reported that people with diabetes are twice as likely to develop Alzheimer's disease. Published in the journal Neurology, it found that even people with a level of poor glucose control that precedes diabetes were 35 per cent more likely to develop some type of dementia. An estimated 1 in 10 cases of dementia may be attributable to diabetes, says neurologist Geert Jan Biessels of Utrecht University in the Netherlands. The failure to find effective treatments for Alzheimer's disease has caused researchers to look at the link to diabetes and other diseases. The association between the two disorders is complicated. Researchers are exploring two general avenues: one to do with vascular disease and the other with blood sugar control. The fact that vascular disease can lead to dementia has been known for some time. Damage to blood vessels in the brain in the form of mini-strokes that decrease blood flow and kill cells can cause so-called vascular dementia — and diabetes is one of the illnesses that can accelerate this type of brain injury. Alzheimer's is different, but diabetes appears to play a role in that process too. Some researchers believe poor blood sugar control can make it harder for the body to clear the build-up of amyloid. Others suspect high levels of glucose create a kind of toxicity in the body related to oxidative stress, in which harmful free radical molecules damage tissue. Genetics also suggests that the two diseases are linked. People with a mutation known as ApoE4 have a higher risk for both Alzheimer's disease and diabetes.