Auburn, Feb. 23---Many scientists have assumed for a long time that genes are the biggest determinant of Alzheimer’s disease.

Now, a new study challenges that assumption.

The study showed African-Americans living in Indianapolis were more than twice as likely to develop neurological disease as Africans living in a Nigerian city of Ibadan. The rate of dementia among African-Americans, in fact, was about 3.24 percent in the United States, compared with about 1.4 percent in Nigeria. The largest share of this neurological disease in the United States was attributable to Alzheimer’s disease.

Nigerians and African-Americans were compared in the study because of their close genetic similarity.  Like Nigerians, the African-Americans in this study were predominantly of West African descent.

The widely different rates of neurological disease between African Americans and Nigerians provide the strongest proof yet that environmental factors, such as diets, may play a bigger role in Alzheimer’s disease than first believed, says Dr. Robert Keith, an Alabama Cooperative Extension System nutritionist.

"While they’re still sorting things out, what we do know is that there is far less hypertension, high blood cholesterol, obesity and diabetes among Nigerians than among Americans of the same descent have over here," Keith says.

Science already has established a strong link between these adverse conditions and vascular disease, a problem most often associated with heart attacks and strokes

Could there also be a link to Alzheimer’s disease?

Several studies already have revealed clues – hints, as Keith would describe them – that people who consume diets high in fruits, vegetables and ascorbic acid-rich foods may be less prone to Alzheimer’s disease.

While conclusive proof of this link is still beyond our grasp, the latest study revealed a host of intriguing clues, Keith says.

"It could be that Alzheimer's is, in some way, linked to impaired blood flow to the brain or free radical damage to the brain – a factor that may work in very subtle ways to distort brain/oxygen content," Keith says.

Numerous studies have shown fruit and vegetable diets appear to promote less high blood pressure, obesity and diabetes and high cholesterol simply because people who consume these types of foods are less prone to eat high-fat, high-cholesterol foods.

However, the link between diet and Alzheimer’s disease may go deeper than that, Keith says.

"It could be that the antioxidant vitamins C and E as well as phytochemicals antioxidants commonly found in these fruits and vegetables that protect against cardiovascular damage also may also be a factor in Alzheimer’s disease."

Antioxidant vitamins, such as C and E, for example, appear to play a vital role preventing the buildup of arterial plaque, a precursor of cardiovascular disease.

Plaque most often begins to occur after some kind of injury takes place along the walls of an artery. The most serious problems occur when cholesterol, damaged by naturally occurring substances in the body, known as free radicals, begin oxidizing and forming within these arterial walls.

"Eventually, what you get resembles a scab," Keith says. "When it gets big enough or a piece of it breaks off, it occludes the artery and, eventually, a heart attack or stroke may occur."

Antioxidants apparently safeguard against this process by reducing levels of free radicals in the body that appear to promote cholesterol oxidization. They also may directly protect the brain against free radical damage.

In the end, scientists may determine diet may safeguard against Alzheimer’s Disease by safeguarding against cardiovascular damage, which causes impaired blood flow to the brain, or by directly protecting the brain from free radical damage.

The search for environmental causes of Alzheimer’s disease is nothing new. Several years ago, after detecting excessive levels of aluminum in the areas of the brain where Alzheimer's disease damage had occurred, scientists began to suspect a strong link between exposure to this material and the likelihood of developing the disease. Subsequent studies, however, have come up empty-handed.

Still other studies have shown that improved physical fitness, keeping the mind sharpened through constant use, and (among postmenopausal women) using hormone replacement therapy may play roles in reducing the incidence of Alzheimer’s disease.

That is why many experts are so excited about the Nigerian study, Keith says. It may finally enable scientists to point out the environmental factors that may contribute directly to Alzheimer’s disease.

Robert Keith, Alabama Cooperative Extension System nutritionist, 334-844-3273.