Alzheimer's Disease Risk Factors

Down Syndrome

Nearly all patients who inherit Down syndrome develop changes in the brain that resemble Alzheimer's if they live into their 40s, although onset varies and can occur as late as age 70. Women under the age of 35, but not older mothers, who give birth to children with Down syndrome are also at much higher risk for Alzheimer's.

Other Risk Factors Associated with Alzheimer's Disease

Lower Education and Economic Groups. A number of studies have reported either a higher risk for Alzheimer's disease in people with less education or a lower risk for Alzheimer's disease in those who remain mentally active. Some experts speculate that learning itself may stimulate more neurons to grow and thus create a larger reserve in the brain so that it takes longer for brain cells to be destroyed. Some evidence suggests that early malnutrition, which is more likely to occur in lower income and educational groups, has been associated with smaller brains and with Alzheimer's disease in old age. Low-birth weight can cause problems in growth factors that could affect both mental and physical health later on in adulthood.

Small Head Size. The size of the skull is fixed by age 7. Brain size approximates the head size until old age, when it begins to shrink. Some evidence has reported an association between small head size (and therefore less brain volume) and Alzheimer's disease, possibly because people who start with larger brains can sustain more injury over time. For example, a 2002 study indicated that it was reduction in overall brain volume, not specific regions, that contributed to mental impairment in older healthy adults. Another study reported that people who had small heads plus the ApoE4 gene had 14 times the risk for Alzheimer's disease than those without this combination. Nevertheless, other studies have found no association between a small head size and Alzheimer's disease.

Some experts suggest that the relationship observed in other research may simply be due to social and economic factors, such as malnutrition or low birth weight, which have been associated with both Alzheimer's disease and small head size. Small head size independent of other factors, they argue, does not pose a higher risk for either Alzheimer's disease or low intelligence