October 10, 2005
Middle-aged and seriously overweight? You may be setting the stage for Alzheimer's disease later in life, a large new study has found. Researchers from Sweden report that compared to individuals who maintain a healthy weight during their middle years, men and women who are obese at midlife have an increased risk for Alzheimer's disease and other forms dementia as they age.
Investigators at Stockholm's famed Karolinska Institute examined 1,449 older men and women living in Finland. They ranged in age from 65 to 79 and were given extensive physical, medical, and cognitive exams to look for signs of heart disease, Alzheimer's, and other ailments. All the study participants had previously been examined at various times during the 1970s and 1980s, when they were in their forties and fifties, so the researchers knew their medical and mental status over more than two decades.
The researchers discovered that obese men and women that is, those with the highest BMI, or body mass index during their middle years had about twice the likelihood of developing Alzheimer's disease and other forms of dementia later in life compared to those with a healthy BMI. BMI is a formula doctors use that takes into account both height and weight to estimate body fat and the likelihood of developing health problems due to excess weight.
People at a healthy weight generally have a BMI under 25. Those with a BMI of 25 to 30 are considered to be overweight, while those with a BMI over 30 are considered obese. A man who is 5 foot 11 and weighs 180 pounds, for example, has a BMI just over 25, while a 5 foot 4 woman who weighs 145 would have a similar BMI on the healthy-overweight border. The National Institutes of Health has a handy BMI calculator on the Web.
What the Study Showed
In the current study, one third of the seniors had a BMI lower than 25 (normal weight) during their middle years, half had a BMI from 25 to 30 (overweight), and the remaining 16 percent had a BMI higher than 30 (obese) at midlife. More than two decades later, 61 of them had developed some form of dementia, including 48 with Alzheimer's disease. Midlife obesity approximately doubled the risk of developing dementia later in life. Being overweight in midlife, as opposed to being obese, however, was not significantly associated with dementia later in life.
"This study shows that obesity at midlife may increase the risk of dementia and Alzheimer's disease later in life," the authors write. High blood pressure and high cholesterol levels were also significant risk factors for late-life dementia, each likewise doubling the dementia risk. Those with the highest midlife BMI were also more likely to have had a heart attack or to suffer from diabetes.
Having all three risk factors midlife obesity, high blood pressure, and high cholesterol was an especially unfavorable constellation. "Clustering of these vascular [heart and blood vessel] risk factors increased the risk of dementia and Alzheimer's disease in an additive manner," the authors report, "so that persons with all three risk factors had around a six times higher risk for dementia than persons having no risk factors." Results appeared in the Archives of Neurology, a medical journal from the American Medical Association.
This study forces us to ask whether the increased risk of dementia conferred by midlife obesity can be altered if individuals lose weight in later life. In other words, are we stuck with the consequences of our midlife lifestyles even if we change later on? To answer this question, the study would have had to determine whether those who were obese during midlife remained obese in later life. If they had, then increased dementia might be the result of obesity in later life. This study did not address these questions, so if you were obese in midlife, you still may be able to lower your risk of dementia now if you lose weight.
Public health experts caution that obesity is on the rise all over the world, including among young people in the United States. This trend is especially ominous, given that excess pounds increase the risk for heart disease and, studies such as this one indicate, Alzheimer's disease as well. The study adds to a growing body of evidence that excess pounds in your earlier years may increase Alzheimer's risk in old age.
Miia Kivipelto; Tiia Ngandu; Laura Fratiglioni; et al: "Obesity and Vascular Risk Factors at Midlife and the Risk of Dementia and Alzheimer Disease." Archives of Neurology, Volume 62, Number 10, pages1556-1560, October 2005.