Alzheimer?s disease may be more common among people with a small waist and large hips than it is among people with the opposite proportions, researchers suggest. The measurement of the waist relative to the hips, called the waist-to-hip ratio, measures the distribution of body fat. People carrying extra weight around their waist (a ?high’? waist-to-hip ratio) are thought to be at increased risk of heart disease and type 2 diabetes compared with those carrying extra weight around their hips (a ?low? waist-to-hip ratio). Dr. Eric B. Larson and colleagues from the University of Washington in Seattle found that the group with the lowest waist-to-hip ratios were about three times more likely to develop Alzheimer?s disease than those with a high waist-to-hip ratio.

Larson?s team studied over 2,500 elderly people who were free of Alzheimer?s symptoms at the beginning of the study. They collected data on the participants? physical characteristics, including height, weight, blood pressure and age, and they measured the circumference of their head, waist and hips.

During the study period, a total of 89 participants developed Alzheimer?s disease. These individuals had similar physical characteristics to those who did not develop the disease, with one exception: they had a lower waist-to-hip ratio. This result held true even when taking into account other factors that could have influenced the risk of Alzheimer?s, such as body weight and gender.

According to Larson, the most obvious explanation for this finding is that people with low waist-to-hip ratios are more likely to survive long enough to develop Alzheimer?s because they are less likely to have heart disease and diabetes. ?However, we are most interested in whether early life development or genetic factors might influence the risk in and of themselves,? says Larson.

To read more, click here plus a key gene variant, are at increased risk of developing Alzheimer?s Disease, according to Dr. Amy Borenstein Graves of the University of South Florida in Tampa. She suggests a head circumference of less than 21.4 inches puts people at greater risk for the disease. However, small head size alone does not increase the risk – they also have to have the e4 variation of the ApoE gene, which produces a protein that helps control levels of fats in the blood.

APOE is short for apolipoprotein E, a molecule involved in the production of sticky plaques in the brain, and the e4 form of the gene is a powerful predictor of Alzheimer?s risk. People with one or two copies of the e4 form of APOE have been found to be at five times the risk of developing the disorder as those without a copy. Dr. Borenstein Graves says people with both risk factors are 14 times more likely to develop Alzheimer?s. In her study, 18% of the risk of Alzheimer?s was ?directly attributable to small head size.? The study followed 1,869 healthy Japanese Americans living in the Seattle area who were 65 or over for just under four years. Information about whether they had the key gene was only available for 59% of those involved. Those who developed the disease were also older, less educated, shorter, lighter and had a lower estimated verbal IQ than those who did not. She admits that the impact of the study is limited because it was done only in the Japanese American population, but says her findings have been confirmed in other populations.

The reason, Graves suspects, is that a smaller head holds fewer brain cells, so there?s less ?reserve? to lose from the disease. ?If you?re going to get the disease, small head size created more impairment,? Graves says. When brain reserve gets built up or how it?s kept stocked isn?t clear. ?Those with large brains may have the same changes in the brains, but they don?t show symptoms of the disease until much later,? she says. It may be possible to retain more brain cells by preventing the brain damage that occurs during a person?s lifetime. While genetics play a part in brain growth, it is also influenced in childhood by factors such as malnutrition, poverty, infection and birth order. Later in life, factors such as higher education, income and mental and physical exercise could play a part.

Does a small skull mean we have fewer brain cells? Dr. Lon White, an epidemiologist who studies brain disorders at the Pacific Health Research Institute in Honolulu, says it works the opposite way, because the skull molds to fit the matter inside so ?in most people the head is as big as the brain makes it be.? Malnutrition, head injury or other factors during early childhood development can ?prevent the brain from becoming as large as it?s genetically programmed to grow.?

During the intensive educational years of adolescence, neural increase but they can be reduced later if they?re not continually reinforced by mental stimulation in young adulthood, middle age, and beyond. It?s the ?use it or lose it? concept of neurology. ?If you have more neurons at some point, you have a bigger head,? Graves says. ?But the density of connections is also important. That?s why keeping your brain active in later life? can guard against dementia.

?It is interesting to speculate on whether we could prevent this disease if we could systematically boost our brain reserves throughout life,? says Graves. ?If it were possible to increase brain reserve through prevention of brain damage that occurs throughout the life span, nearly 20% of the disease among these individuals might be [avoidable].?

Dr. Richard Harvey, of England?s Alzheimer?s Society, disagrees and says measuring head circumference is unreliable and that studies measuring the size of the space within the skull through scans found no difference between people who had had Alzheimer?s and those who did not. He says that even the basic measuring of circumference is difficult to do accurately. ?If you have to measure the circumference of people?s heads and someone else did it, they are likely to get a different measurement.?

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