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Risk factors

Alzheimer's is a complex disease likely caused by a combination of factors — such as infection or reduced circulation — and genetic susceptibility. Although all the contributing factors may never be known, scientists have identified several common threads. They include:

• Age. Alzheimer's usually affects people older than 65, but can, rarely, affect those younger than 40. Less than 5 percent of people between 65 and 74 have Alzheimer's. For people 85 and older, that number jumps to nearly 50 percent.
• Heredity. Your risk of developing Alzheimer's appears to be slightly higher if a first-degree relative — parent, sister or brother — has the disease. Although the genetic mechanisms of Alzheimer's among families remain largely unexplained, researchers have identified a few genetic mutations that greatly increase risk in some families. Three genetic mutations are known to cause early-onset Alzheimer's. In addition, one form of the apolipoprotein E (APOE) gene increases your chance of developing late-onset Alzheimer's.
• Sex. Women are more likely than men are to develop the disease, in part because they live longer.
• Lifestyle. The same factors that put you at risk of heart disease, such as high blood pressure and high cholesterol, may also increase the likelihood that you'll develop Alzheimer's disease. Poorly controlled diabetes is another risk factor. And keeping your body fit isn't your only concern — you've got to exercise your mind as well. Some studies have suggested that remaining mentally active throughout your life, especially in your later years, reduces the risk of Alzheimer's disease.
• Education levels. Studies have found an association between less education and the risk of Alzheimer's. Some researchers theorize that the more you use your brain, the more synapses you create, which provides a greater reserve as you age. It remains unclear, however, whether less education and less mental activity create a risk of Alzheimer's or if it's simply harder to detect Alzheimer's in people who exercise their minds frequently or who have more education.
• Toxicity. One long-standing theory is that overexposure to certain trace metals or chemicals may cause Alzheimer's. For a time, aluminum seemed a likely candidate, because some people with Alzheimer's have deposits of aluminum in their brains. After many years of studies, however, no one has been able to link aluminum exposure directly to Alzheimer's. At this point, there's no evidence that any particular substance increases a person's risk of Alzheimer's.
• Head injury. The observation that some ex-boxers eventually develop dementia suggests that serious traumatic injury to the head (for example, a concussion with a prolonged loss of consciousness) may be a risk factor for Alzheimer's. Several studies indicate a definite link between the two, but others show no link.
• Hormone replacement therapy. The exact role hormone replacement therapy may play in the development of dementia isn't yet clear. Throughout the 1980s and '90s, evidence seemed to show that estrogen supplements given after menopause could reduce the risk of dementia. But results from the large-scale Women's Health Initiative Memory Study indicated an increased risk of dementia for women taking estrogen after age 65. The verdict is not yet in on whether estrogen affects the risk of dementia if given at an earlier age.Penyebab Alzheimer