By Sandee LaMotte

Having high cholesterol and blood sugar in your 30s may raise your risk for Alzheimer's disease decades later in life, according to a new study.

"We have shown for the first time that the associations between cholesterol and glucose levels and the future risk of Alzheimer's disease extend much earlier in life than previously thought," said senior study author Lindsay Farrer, chief of biomedical genetics at Boston University Biomedical Genetics.

"This study gives us more fuel for the fire that we need to start as early as possible in the fight against Alzheimer's," said Dr. Richard Isaacson, director of the Alzheimer's Prevention Clinic in the Center for Brain Health at Florida Atlantic University's Schmidt College of Medicine. Isaacson was not involved in the study.

A type of cholesterol and blood sugar

People ages 35 to 50 who had high levels of triglyceride, a type of cholesterol found in blood, and lower levels of the "good cholesterol" called high-density lipoprotein were more likely to be diagnosed with Alzheimer's disease later in life, the study found.

"In the early age group (35-50 years) only, an increase of 15 mg/dL (milligrams per deciliter) in triglycerides was associated with an approximate 5% increase in Alzheimer's disease risk," Farrer said via email.

The association was not seen for older age groups, perhaps because older adults are treated for cholesterol more aggressively, he said.

"Alternatively, it could reflect that high triglycerides in early adulthood may trigger a cascade of metabolic events that over time initiate processes that directly lead to Alzheimer's disease," Farrer said.

In people ages 51 to 60, it was higher blood sugar levels that raised the risk for Alzheimer's, according to the study.

"For every 15 points that your blood sugar goes up, your risk of Alzheimer's goes up by 14.5% later in life," said Farrer, who is also a professor of medicine, neurology, ophthalmology, epidemiology and biostatistics at Boston University School of Medicine.

"Having high cholesterol may not cause Alzheimer's, but it presses the fast-forward button on the disease pathology and cognitive decline," Isaacson said. "There's also a relationship between diabetes and the development of amyloid pathology."

Beta amyloid plaques in the brain are one of the hallmark signals of Alzheimer's, along with tangles of a protein called tau.

"Just like any chronic disease of aging -- high cholesterol, heart attacks, strokes -- they all start silently decades before they show up. Alzheimer's disease is no different," Isaacson said. "Targeting them early on is the best recipe for optimal brain health as we age."

Raising HDL helps

The study, published Wednesday, followed people enrolled in the Farmingham Heart Study, a government-supported study that is now in its 74th year.

"What's unique about the study is the large sample of individuals that are examined every four years or so, starting at age 35, and followed into the age when an Alzheimer's diagnosis may occur," Farrer said.

There was some good news from the study: People 35 to 50 could lower their Alzheimer's risk by 15.4% if they raised their high-density lipoprotein, or HDL, by 15 milligrams per deciliter. People between the ages of 51 and 60 who raised their HDL reduced their risk by 17.9%.

High-density lipoprotein is called the "good cholesterol" because it gathers up the bad stuff floating in the bloodstream and takes it to the trash (the liver), where it is flushed from the body. The US Centers for Disease Control and Prevention states that high HDL levels can be protective against heart disease and stroke. Levels of HDL should be at least 40 milligrams per deciliter for men and 50 milligrams per deciliter for women, according to the Cleveland Clinic.

People who wish to tackle their cholesterol should work carefully with a preventive cardiologist and neurologist, as there are many nuances to how to measure blood lipids and which medications are best, Isaacson said.

"The take-home message is that people who are in their 30s and early 40s need to have their lipids and blood sugar measured. That's the only way you'll detect any issues," Farrer said.

"But many people that age feel they're healthy and say, 'Why do I need to see a doctor all the time?' So it's encouragement for people to start having regular checkups at that period of your life," he added.