A new study adds to growing evidence that the complications of diabetes may extend to the brain, causing declines in memory, attention and other cognitive skills.
The new research showed that over the course of about a decade, elderly men and women with diabetes -- primarily Type 2, the form of the disease related to obesity and inactivity -- had greater drops in cognitive test scores than other people of a similar age. The more poorly managed their disease, the greater the deterioration in mental function. And the declines were seen not just in those with advanced diabetes. The researchers found that people who did not have diabetes at the start of the study but developed it later on also deteriorated to a greater extent than those without the disease.
"What we've shown is a clear association with diabetes and cognitive aging in terms of the slope and the rate of decline on these cognitive tests," said Dr. Kristine Yaffe, a professor of psychiatry and neurology at the University of California, San Francisco. "That's very powerful."
加州大学旧金山分校(University of California, San Francisco)精神病学及神经病学教授克里斯廷·亚菲博士(Dr. Kristine Yaffe)说：“我们展示出了糖尿病与老年人的认知衰老之间，存在清晰的联系。认知衰老是以认知测验得分下降的坡度和比率衡量的。这个结果非常有力。”
While correlation does not equal causation and the relationship between diabetes and brain health needs further study, the findings, if confirmed, could have significant implications for a large segment of the population. Nationwide, nearly a third of Americans over the age of 65, or roughly 11 million people, have diabetes. By 2034, about 15 million Medicare-eligible Americans are expected to have the disease.
Previous studies have shown that Type 2 diabetes correlates with a higher risk of Alzheimer's disease and dementia later in life. But how one leads to the other has not been well understood. While some scientists speculate that inflammation and vascular damage caused by chronically high blood sugar levels over many years is the culprit, findings from research have been inconsistent. And until now, little was known about the effect, if any, that newly diagnosed diabetes would have on cognitive function.
In the new study, published in Archives of Neurology, Dr. Yaffe and her colleagues relied on extensive data from the Health, Aging and Body Composition project, or Health ABC, a long-running study of white and black older adults living in Pittsburgh and Tennessee. The researchers looked at 3,069 people, many of them in their 70s. When the study began, 23 percent of the subjects had diabetes. And 5 percent were free of diabetes at the outset but went on to develop it later.
这项新研究发表在《神经病学档案》(Archives of Neurology)上。亚菲博士和她的同事是根据健康ABC项目中的大量数据进行的这项研究。健康ABC全称健康、衰老和身体成分(Health, Aging and Body Composition)项目，该项目长期对居住在匹兹堡和田纳西州的老年白人和黑人进行研究。 研究人员调查了3069人，其中很多人的年龄在70至79之间。研究开始时，23%的研究对象患有糖尿病。5%的研究对象在研究开始时没有糖尿病，但后来患病。
While the researchers did not distinguish between Type 1 and Type 2 diabetes, they said that given the average age of the subjects, about 74, most if not all had Type 2 diabetes.
Over the course of the research, the subjects were repeatedly given cognitive tests that looked at things like their memory, their coordination, dexterity and ability to concentrate, as well as their overall mental health. At the start of the study, those who already had diabetes had slightly lower baseline scores than the subjects who did not have the disease.
But nine years later, the gap in cognitive test scores had widened significantly between those with and without diabetes. The differences remained even after the researchers adjusted their results for the effects of age, race, sex and education. They also found that the subjects who were free of diabetes at the beginning of the study but developed it later on had scores that fell between those of the other two groups.
The researchers then delved further by looking at the effect of poor glucose control. In this case, they took measures of something called glycosylated hemoglobin. Unlike traditional blood sugar tests, which provide a momentary snapshot of a person's glucose levels, glycosylated hemoglobin gives doctors a much broader picture, providing an idea of blood sugar management over the course of weeks. It is considered one of the best ways for doctors to assess the progress of diabetes treatment.
In the new study, higher measures of the compound, which indicate poorer control of blood glucose levels, were the best predictor of cognitive decline.
The findings suggest that more aggressive approaches to managing and especially preventing diabetes in midlife or before may help stave off mental declines in large segments of the population. But Dr. Yaffe warned that doctors should be cautious about lowering blood sugar levels too far in elderly diabetics, since they are especially vulnerable to the effects of hypoglycemia.
"There's this idea that the better your glucose control, the better off you are in terms of trying to prevent complications of diabetes," she said. "But in older people it's a slippery slope. The elderly are more sensitive to hypoglycemia, they've got other medications that may interact, and they've got other conditions."
"When you lower their blood sugar levels too aggressively," she added, "you might do more harm than good."