A wide range of occupations, from farming to teaching, may be potential risk factors for degenerative brain diseases, such as Alzheimer’s and Parkinson’s disease, research findings suggest.

In a study of more than 2.6 million U.S. death records, researchers found that a variety of jobs were associated with an increased risk of death from several forms of brain degeneration, namely Alzheimer’s and Parkinson’s disease, early-onset dementia and motor neuron disease.

Many of the associations had been seen in earlier research and could potentially be explained by on-the-job exposures to the chemicals that farmers, welders and hairdressers routinely use or inhale.

Other findings, however, such as the elevated disease risks among teachers, clergy and bank tellers, are not easily explained, according to the researchers, led by Robert M. Park of the National Institute for Occupational Safety and Health, Cincinnati, Ohio.

Studies such as this, where death certificates are used to find associations between occupation and disease risk, have their limits. For one, death records are a less-than-ideal measure of a person’s work history, Park told.

“At best,” he noted, such research can tease out general patterns that can then be studied further.

In their analysis, Park and his colleagues found that the bank tellers, clergy, aircraft mechanics and hairdressers had highest odds of dying from Alzheimer’s disease. For Parkinson’s disease, the highest risks were among biological scientists, teachers, clergy members and other religious workers.

The risk of death from presenile dementia - a form of dementia that arises before the age of 65 - was greatest among dentists, graders and sorters in industries other than agriculture and, again, clergy.

Veterinarians, hairdressers and graders and sorters had the highest risks of dying from motor neuron disease, the most common form of which is amyotrophic lateral sclerosis, also known as Lou Gehrig’s disease - an invariably fatal degeneration of the central nervous system that causes muscle wasting and paralysis.

The findings, based on death records from 22 states for the years 1992 to 1998, are published in the American Journal of Industrial Medicine.

Of all deaths for those years, just over 4 percent were attributed, at least in part, to a neurodegenerative disease.

These diseases are marked by progressive, irreversible damage to cells of the central nervous system. It’s thought that genes influence susceptibility to the conditions, but growing evidence also points to environmental factors, including some on-the-job exposures.

For example, farmers exposed to pesticides have been shown in some studies to have a higher-than-average risk of Parkinson’s disease, as have welders exposed to fumes containing the mineral manganese. Both of these occupations were associated with Parkinson’s in the current study as well.

Hairdressers were at increased risk of death from Alzheimer’s disease, presenile dementia and motor neuron disease. These findings, Parker and his colleagues note, suggest a role for hair dyes, solvents or other chemicals used in salons.

Other job-disease relationships, including the higher risks for several neurodegenerative conditions among teachers and clergy, “are difficult to interpret,” according to Park.

One possibility, he and his colleagues note in the report, is that people in professional jobs have lower risks of common, lifestyle-related diseases like heart disease, which makes them more likely than others to die of a neurodegenerative disorder.

As for dentists, dental assistants and veterinarians, there may be a role for certain occupational exposures, the researchers speculate. In the case of dentistry, that could include exposure to mercury or synthetic substances used in dental work. The finding on vets, they add, could signal a role for some yet-unidentified chemical or biological substance.

SOURCE: American Journal of Industrial Medicine, July 2005.