The list of health risks for diabetics is already long, including kidney failure, nerve damage, heart disease, stroke, bladder control problems, and erectile dysfunction.

Now, research from Japan has added another complication to that list: People with diabetes are at increased risk of getting Alzheimer’s or other types of dementia.

Researchers from Kyushu University in Fukuoka, Japan had more than 1,000 adults take a glucose tolerance test in 1988 to see how well their bodies processed blood sugar. Then, the researchers followed up with them over the next 15 years.

Over the course of the study, 232 people developed dementia. People who had been diagnosed with diabetes had a 74 percent greater risk of being diagnosed with some type of dementia than those who had normal glucose levels – even after taking account of other risk factors, including age, body mass index, and several lifestyle choices.

People who had impaired glucose tolerance were 35 percent more likely to develop dementia, the researchers found.

The study is published in Neurology and the link has ominous implications. There are more than 25 million diabetics in the U.S. alone – a number that’s expected to skyrocket in coming years. Alzheimer's cases are also already projected to climb significantly in the next two decades as the population ages; increases in patients with diabetes may worsen that number.

How are they connected?

Researchers are still trying to sort out how and why diabetes would contribute to an increased risk of dementia. They have some possible explanations, but no concrete evidence.

Several theories revolve around the idea that diabetes affects the ability of the brain and other body tissues to use sugar and respond to insulin. Insulin resistance may interfere with the body’s ability to break down a protein that forms brain plaques linked to Alzheimer’s. Diabetes may also damage cells and blood vessels, causing oxidative stress and metabolism problems.

Another possibility is diabetes role in hardening arteries and microvascular disease, both of which would limit blood flow to the brain.

While scientists sort out exactly what's going on, it’s safe to say habits that help lower diabetes risk, such as getting regular exercise, eating a healthy diet and not smoking, also improve the health of your brain. Taking steps to prevent diabetes could also protect your memory in the long run.

If you have diabetes, taking steps to carefully control it, like lowering high cholesterol and blood pressure, could keep you from harming the brain's blood supply and exacerbating memory problems.