Medical and nutritional researchers once assumed that among certain genetically prone people, dementia was as inevitable as death and taxes.
Now, based on new findings, they are revising this picture. A wealth of studies conducted within the last couple of decades has presented these researchers with a radically different picture: With the exception of Alzheimer's disease, one's chances of developing dementia, while affected by genetic factors, may also be significantly influenced by lifestyle practices.
For example, a study completed almost a decade ago revealed that American participants of West African descent living in Indianapolis were almost twice as likely to develop some form of neurological disease as Africans living in the Nigerian city of Ibadan.
The widely different rates of neurological disease between two genetically similar groups provided some of the strongest evidence up to that time that environmental factors also played a role, says Dr. Robert Keith, an Alabama Cooperative Extension System nutrition and fitness specialist and Auburn University associate professor of nutrition and food science.
However, Keith adds what he describes as an important qualifier: Based on recent findings by a National Institutes of Health Panel, lifestyle factors may not be as effective in staving off Alzheimer's disease as they are other forms of dementia.
The study also revealed significantly less hypertension, high blood cholesterol, obesity and diabetes among Nigerian men than their American counterparts, Keith stresses.
Except for Alzheimer's disease, research continues to reveal a strong link between unhealthy lifestyles and dementia.
For example, one long-term study involving more than 6,500 people in northern California found that those who were fat around the middle at age 40 were more likely to develop dementia in their 70s. A similar study conducted in Sweden revealed a similar finding.
Studies have also revealed signs of brain damage among obese people. For example, a study of 60 healthy adults in their 20s and 30s revealed that heavier members possessed significantly lower gray matter densities in several brain regions. Likewise, another study found that among 114 participants, the obese ones tended to have smaller, more atrophied brains than the thinner ones.
"Brains usually atrophy with age, but being obese appears to accelerate the process," says evolutionary biologist Dr. Olivia Judson, who reviewed the findings recently in the New York Times.
Even so, genetic influences do appear to play at least some role. In fact, scientists have identified one gene, known as FTO, which appears to affect body weight and function. One version of this gene appears to be especially troublesome.
"Individuals with two copies of the troublesome version tend to be fatter than those with one copy of it, who in turn tend to be fatter than those with two copies of the regular version," she says. "Now the troublesome form has been linked to atrophy in several regions of the brain, including the frontal lobes, though how and why it has this effect remains unknown."
Still, genetic influences appear to be only part of a much wider picture, says Keith.
Within the last few decades, researchers have uncovered a host of other lifestyle factors associated with reduced brain function, with smoking at the top of the list, says Keith.
Toxins associated with smoking have been shown time and again to be harmful to the brain.
"If you smoke a lot, you're going to get these toxins entering into and damaging your brain," Keith says.
But these toxins can damage the brain in less direct ways too, such as causing arterial damage, which, over time, impedes blood flow to the brain. Smoking also increases blood pressure, which ultimately can cause TIAs, transient ischemic attacks — ministrokes to the brain.
Carbon monoxide inhaled from smoking also replaces oxygen in red blood cells, which results in the brain getting less oxygen.
Any kind of cardiovascular disease that undermines blood vessel function also has the potential of impeding brain function, Keith says.
Type-2 diabetes, often closely tied to obesity, also affects cardiovascular health and, ultimately, brain function.
"If you have type-2 diabetes and you're secreting a lot of insulin over a period of years, this insulin has been shown to be detrimental to the brain," Keith says.
Sleep apnea, another chronic condition closely tied to obesity, typically starves the brain of oxygen and may possibly even lead to brain damage.
Finally, fat tissue itself may be a problem. Fat cells secrete hormones such as leptin, which affect the brain in sundry ways. In fact, leptin may contribute to Alzheimer's disease.
"Whatever the causes, the implications are grave," says Judson. "In the United States States today, around one-third of adults are obese."
Equally disturbing, dementia is one of the costliest and most devastating diseases associated with aging.
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