I was asked recently about the relationship between diet and Alzheimer's disease. This is a great question since we tend to focus on more traditional health benefits of eating well, such as heart disease, stroke and diabetes. This was in response to a recent study published in the journal Neurology.
In that study, Swedish researchers looked at 8,534 twins over the age of 65. Thirty percent of those studied were overweight or obese. The risk of dementia was almost double in those who were overweight versus those of normal weight. Alarmingly, those who were obese had almost a fourfold increase in risk.
This research supports many studies in the last few years that associate both being overweight and metabolic syndrome with increased risk of dementias. While most people use the term Alzheimer's to describe dementia, there are lot of other causes. For instance, multi-infarct dementia is very common and is a process of damage to small blood vessels in the brain in the same way that causes heart and peripheral vascular disease.
It's clear that obesity, especially central fat (belly fat), puts people at risk. In an early study, researchers with Kaiser Permanente of Northern California looked at whether being apple-shaped (which is by itself a strong risk for diabetes and heart disease) would also be a strong risk for dementia (that study was published in 2008 in the journal Neurology). They identified current members of the HMO who had been continuous patients between 1964 and 1973 and were between 40 and 45 years of age at that time. In that nine-year period, all of the eligible patients had their blood pressure and cholesterol levels, height, weight, waist measurement and thigh circumference measurement taken as part of their routine medical care.
In 2006, the endpoint of the study, a group of eligible patients of more than 6,500 men and women were still alive and still members, although they were then between 73 and 87 years of age. More than 1,000 of the 6,500 men and women had been diagnosed with dementia between 1994 and 2006. Their waist and thigh measurements were compared with those who were not diagnosed with dementia.
The waist measurements of all patients were grouped into five sections of increasing waist measurements, beginning with normal waist circumference for the individual's body mass index (BMI, a measure of weight and height). Compared with those with normal waist circumference, those at the highest waist circumference saw their risk of dementia increase by almost 300 percent.
Even when the researchers adjusted for BMI across the board, the highest levels of waist circumference meant that an individual's risk of dementia was still increased by almost 200 percent. By contrast, those whose BMI was in the overweight or obese ranges but who were pear-shaped had their risk of dementia only increase by 80 percent. (This does not mean that being pear-shaped protects from the long-term consequences of obesity; it just means that the risks are not as high as those whose body fat is carried mainly in their belly.)
Scientists in the United Kingdom and Australia looked at this in a similar, but smaller, retrospective study. They sought to establish a direct link between metabolic syndrome and Alzheimer's by selecting 50 patients with probable Alzheimer's from memory disorder clinics in Australia and England (their study was published in 2007 in the Archives of Neurology). 75 control patients were recruited from the Alzheimer's patients' spouses and from the surrounding communities. All 125 subjects were given full medical exams, including height and weight, waist circumference, blood pressure and blood tests to measure glucose levels and cholesterol scores. In addition, they were given Mini Mental Status Examinations (MMSE) to confirm dementia (for the Alzheimer's patients) or the lack thereof (for the control subjects).
They found that those with metabolic syndrome increased their risk of Alzheimer's by three times compared with those without the syndrome. Interestingly, Alzheimer's patients tended to have high blood pressure less frequently than those with a normal score on the MMSE, and those with high blood pressure seemed to have a reduced risk of Alzheimer's.
As always, the question is what to do about this. Weight control is key, but as I have said for a long time, that is only part of the puzzle. A Mediterranean diet can help control that central adiposity, but eating a healthier diet has benefits beyond weight control.
For instance, Dr. Nikolaos Scarmeas and his colleagues published a study on a group of elderly subjects that indicated eating a Mediterranean style diet leads to a lower risk of Alzheimer's Disease (their study was published in 2006 in the journal Archives of Neurology). The study was done in an effort to confirm previous research by Dr. Scarmeas' lab showing a reduced risk in those on a Mediterranean diet. Their first study had looked at people who didn't have any evidence of Alzheimer's at the start of the study, while the follow-up research evaluated those with some degree of dementia. It was a retrospective study where dietary intake for the previous year was assessed.
The results were similar to Scarmeas' earlier work. The participants who scored in the upper third of the defined categories of a Mediterranean diet were found to have a 60 percent lower risk of Alzheimer's disease than people not on the diet.
As I noted earlier, there has been some link between dementia (including Alzheimer's) and vascular diseases, such as the processes that cause heart attack and stroke. In an effort to see if those links might be a factor in their results, the researchers adjusted for participants with any evidence of vascular disease or conditions associated with heart attack and stroke, such as diabetes, hypertension and high cholesterol. In doing so, they found there was an even greater reduction in risk of 68 percent for those with scores in the upper third and 53 percent for the middle third.
In the last six or seven years, there have been dozens of quality studies to support that optimum weight and Mediterranean diet may be linked to lower risk of Alzheimer's and other dementias in a similar way that they are linked to lowering the risk for heart disease, stroke and diabetes. Here's more information on what a Mediterranean diet is and how you can incorporate it into your life.