People with mentally demanding careers appear to have a lower risk for Alzheimer’s disease than peers who had less mentally demanding careers, according to an article in the August 10th issue of Neurology.

The American study examined 122 people with Alzheimer’s disease and 235 people without the disease as a control group. All were over 60 years old. Information about their occupational history from their 20s through their 50s was collected from the control group directly and from family members of those with Alzheimer’s disease.

The information included the type of job and industry, the length in the job, and their most important activities in the job. The mental, physical, social and fine motor skill demands of their jobs were determined using measures developed by the U.S. Department of Labor.

The researchers found that, on average, people with Alzheimer's disease held jobs with lower mental demands than people in the control group. Looking decade by decade at the jobs held by study participants, the researchers found that people with Alzheimer’s disease and those in the control group had jobs with about the same level of mental demands when they were in their 20s. The level was about 15 percent above the average for all U.S. occupations ranked by the Labor Department. However, those in the control group moved on to jobs with higher mental demands in their 30s, 40s and 50s, increasing the demand level by about 33 percent on average across the decades. The mental demands of occupations for those with Alzheimer’s disease remained at about the same level in later decades.

The researchers also found that those with Alzheimer’s disease had jobs with more physical demands than those in the control group during their 20s, 40s, and 50s. They found no differences across the decades in the social or motor demands of jobs held by those with Alzheimer’s disease and those in the control group.

Because education has been found to be protective against Alzheimer’s disease, the researchers reexamined the data while controlling for educational level, and the results did not change. The researchers don’t know what the link is between Alzheimer’s disease and less mentally demanding occupations. Several theories exist.

“It could be that the disease has a very early effect on the individual’s capacity to pursue a mentally challenging occupation,” said Kathleen Smyth, PhD, lead author of the study. “Or, it could be that higher levels of mental demands result in increased brain cell activity, which may help maintain a ‘reserve’ of brain cells that resists the effects of Alzheimer’s disease.”

Smyth added, “There is also the possibility that jobs with higher mental demands require skills that enhance an individual’s ability to perform well on the tests used to diagnose Alzheimer’s. If this is the case, then the disease may go undetected in these people until the disease is much farther along than in those whose jobs pose lower mental demands.”

One limitation of the study was that researchers did not control for socioeconomic status, Smyth said. “People with higher socioeconomic status generally hold jobs with higher mental demands compared to those with lower socioeconomic status,” she said. “Therefore, variations in income, access to health care, better nutrition, and other factors related to socioeconomic status could be responsible in part for our findings.”

The study also did not factor in environmental demands and exposures of occupations. “There could be possible relationships between these factors and the development of Alzheimer’s disease,” Smyth said.