February 21, 2005
Want to lower your risk of developing Alzheimer's? Try losing weight. Older men who maintained a healthy body weight were much less likely to develop Alzheimer's disease than those who were obese. The findings come from a large and ongoing study from Sweden, published in the highly respected medical journal Archives of Internal Medicine. The same research group reported in 2003 that older women who kept their weight down also had a lower risk of developing Alzheimer's disease.
As part of the Primary Prevention Study that began in 1970, researchers at Sahlgrenska University Hospital in Goteburg, Sweden followed 7,402 men for over 20 years. They were given regular medical exams as well as mental and memory tests to look for signs of dementia. They were also surveyed about lifestyle factors such as smoking and physical activities.
The men's body mass index, or BMI, was also recorded. 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. The National Institutes of Health has a handy BMI calculator.
At the start of the study, the men ranged in age from 47 to 55. None of them had Alzheimer's or other major illnesses such as a history of heart attacks or strokes. More than twenty years later, when the men were in their late 60s and 70s, 254 had developed Alzheimer's disease or other forms of dementia, while 7,148 remained free of the illness.
The heavier the men, the researchers found, the more likely they were to develop dementia. After accounting for other possible risk factors, such as high blood pressure, high cholesterol, diabetes, smoking, and education, the scientists found that the leanest men, those with a BMI of around 20, had the lowest risk of developing Alzheimer's. As BMI and weight increased, so did risk. Obese men, with a BMI of 30 and over, were two and a half times more likely to suffer from Alzheimer's and other forms of dementia than the leanest men.
The findings confirm earlier research linking overweight and obesity to Alzheimer's disease. In 2003, as part of the same ongoing study, scientists found that older women who were overweight at age 70 were much more likely to develop Alzheimer's disease 10 to 18 years later.
Teasing out the contributions of weight and other lifestyle factors to Alzheimer's disease, however, remains difficult. In numerous studies, being overweight and obese has been linked to heart disease, diabetes, and other health problems that may damage blood vessels in the brain and contribute to dementia. Just because you are thin, however, doesn't mean you won't have a heart attack or develop Alzheimer's in old age. Similarly, many heavy people never develop memory loss and dementia. Nevertheless, many of the risk factors for Alzheimers disease are the same as those for heart disease, overweight being just one.
The effects of weight on memory and brain function are further complicated by the fact that many people with Alzheimer's disease grow thin. In some cases, weight loss may precede a diagnosis of Alzheimer's by many years.
Age remains the most important risk factor for Alzheimer's. About one in three people who reach age 85 will show signs of Alzheimer's and other forms of dementia. Smoking, high blood pressure, years of schooling, and genetic factors also appear to contribute to risk for these problems. Still, as the results of this study suggest, keeping your weight down during middle age and beyond may help you to remain mentally alert as well.
Annika Rosengren; Ingmar Skoog; Deborah Gustafson; Lars Wilhelmsen: "Body Mass Index, Other Cardiovascular Risk Factors, and Hospitalization for Dementia." Archives of Internal Medicine, February 14, 2005; Volume 165, Number 3, Pages 321-326.