A new study by researchers from the US and Sweden showed that having a large belly in midlife increased the risk of having dementia in old age, with
overweight and obese people with large bellies having double or triple the risk. In other words, while being overweight and obese was a risk factor, the
study showed this was significantly affected by where the weight was carried in midlife.
The study is published in the online issue of the journal Neurology, and was conducted by Dr Rachel Whitmer, who is a research scientist at the Kaiser Permanente Division of Research in Oakland, California, and colleagues.
Previous research has linked waist circumference or central obesity and body mass index (BMI) in elderly people to the risk of developing dementia, and it has also shown that having a large abdomen in midlife is linked to higher risk of heart disease, stroke and diabetes.
But this is the first study to show a link between belly fat in midlife and the risk of developing dementia decades later.
Whitmer and colleagues studied 6,583 health plan members of Kaiser Permanente living in Northern California who had had their sagittal abdominal diameter (SAD) measured between 1964 and 1973 when they were aged between 40 and 45.
SAD, which is a measure of belly density, is taken using a caliper that measures the distance from the back to the upper abdomen, when positioned midway between the top of the pelvis and the bottom of the ribcage.
The researchers explained that the size of the belly at this point is an indicator of the amount of fat tissue that is wrapped around the organs in the abdomen.
By examing medical records between 1994 and 2006, the researchers established that 16 per cent (1,049) of the participants had dementia an average of 36 years later.
Using statistical techniques and adjusting for age, sex, race, education, blood pressure, stroke, and other medical and demographic variables, they examined the links between midlife SAD and dementia incidence.
The results showed that:
- Participants who were overweight and had a large belly in midlife were 2.3 times more likely to develop dementia some 30 years later than those who were of normal weight and belly size.
- Participants who were obese and also had a large belly in midlife were 3.6 times more likely to develop dementia later in life compared with those of normal weight and belly size.
- Participants who were overweight or obese but did not have a large belly in midlife, had an 80 per cent increased risk of dementia.
- Having a high SAD measure, ie larger than normal abdomen, in midlife appeared to increase the risk of dementia regardless of whether the person had normal overall weight, was overweight or obese, and regardless of existing health conditions, including diabetes, stroke and cardiovascular disease.
- Being non-white, having high blood pressure, high cholesterol or diabetes, and less than a high school level of education was closely linked to higher abdominal obesity.
"Central obesity in midlife increases risk of dementia independent of diabetes and cardiovascular comorbidities. Fifty percent of adults have central obesity; therefore, mechanisms linking central obesity to dementia need to be unveiled."
Whitmer suggested that measuring midlife belly size may be a better indicator of long term disruption of metabolism that leads to dementia than using abdominal size in older people because as people age they lose muscle and bone mass and their belly becomes proportionally larger.
She said this was a disturbing finding, considering that 50 per cent of adult Americans have abdominal obesity.
"It is well known that being overweight in midlife and beyond increases risk factors for disease," said Whitmer.
"However, where one carries the weight, especially in midlife, appears to be an important predictor for dementia risk," she added.
Changes in the brain that lead to Alzheimer's can start in young to middle adulthood, as autopsies have revealed, explained Whitmer. Research has also shown that high abdominal fat in older people is linked to higher rate of brain atrophy. However, Whitmer said that:
"These findings imply that the dangerous effects of abdominal obesity on the brain may start long before the signs of dementia appear."
However, the researchers also cautioned that, as with all observational studies, you cannot say these results show that belly size drives dementia risk, the more likely explanation is that it is one of a complex set of inter-related health factors and behaviours.
The researchers called for further studies to investigate the underlying mechanisms that link belly size in midlife to risk of developing dementia later.
Dementia is not a specific disease, it is an umbrella term for a group of symptoms caused by a range of brain disorders that prevents people getting on with everyday life such as eating and getting dressed or going shopping. It impairs memory, language, ability to solve problems, and control emotions, and can change a person's personality or make them anxious or see things that aren't there.
Alzheimer's disease and stroke are two examples of diseases that can cause dementia. Drugs can slow or improve some of the symptoms but there is no cure.
"Central obesity and increased risk of dementia more than three decades later."
Whitmer, R. A., Gustafson, D. R., Barrett-Connor, E., Haan, M. N., Gunderson, E. P., Yaffe, K.
Neurology, Published online before print March 26, 2008.
Click here for Abstract.
Sources: journal abstract, PR Newswire press release, Medline Plus
Written by: Catharine Paddock, PhD