Epidemiology Studies Explore Potential Risk Factors for ALS
One Study: Veterans May Have Higher Risk of ALS; Another Suggests Physical Activity Not a Risk Factor
February 2, 2005
[QUICK SUMMARY: The risk for ALS in men is increased by 50 percent by military service according to one study; another study fails to find that physical activity increases ALS incidence in the general population.]
Two recent studies published in the journal Neurology highlight the challenges in definitively identifying the risk factor or factors linked to ALS. Epidemiology the branch of medicine that attempts to explain the interaction of host, agent, and environment in causing disease is an approach to studying potential risk factors for ALS.
Harvard epidemiologists reported in the January 11 issue that men who served in the military have an increased rate of ALS. In the January 25 issue, a Dutch group reports that physical activity does not increase the incidence of ALS in the general population.
“These studies certainly raise intriguing questions about potential risk factors for ALS and highlight the need for further studies, especially larger case-control studies to more definitively define which factors are linked to ALS,” commented Lucie Bruijn, Ph.D., science director for The ALS Association.
In a study to determine whether there is a higher risk of ALS in the military, Harvard investigators used a data set already available through a cancer prevention study. Data collected after 1989, through 1998, from participants in the Cancer Prevention Study II conducted by the American Cancer Society, identified deaths from ALS, allowing study of the issue of ALS and military service.
The relative risk of dying from ALS for veterans was 1.5 times that seen for the men who did not serve. Of the 281,874 men in the study who served in the military, 217 died of ALS, compared to 63 of the 126,414 who did not serve.
Prior studies have found increased risk of ALS with service during the Gulf War.The current study suggest that the risk for ALS may not be a product of the specific conditions encountered during that conflict, as risk was apparent for veterans of World War II, the Korean War, and the War in Vietnam.
In light of these and previously reported studies on ALS and the military it becomes important to try and identify what the environmental exposures are and whether genetic susceptibility plays a role. In a second article, a Dutch group addresses the question as to whether exercise can be linked to ALS. There have been several published studies implicating exercise and ALS.
It remains unclear whether exercise is indeed a risk factor and what types of exercise may be of concern. Indeed some studies seem to suggest that some exercise may be beneficial. The Dutch case control study compared physical activities during work and leisure for 219 ALS patients and 254 controls. Activities were self-reported, and no increased risk for the disease incidence was apparent with differing amounts of physical activities, at work or during leisure, in this study.
Recognizing the need for larger population based studies, groups in Europe and the
Questions and Answers
Q: Is the risk of ALS also higher for veterans who did not serve during a conflict era?
A: The answer to this question is still unclear and more research is needed to understand the true relationships between military service and ALS. The Gulf War ALS study did find an increased rate of ALS in the troops deployed to the Gulf region as compared to a control group of service personnel not deployed to the Gulf region.
Q: How does the ALS risk for veterans compare to the incidence of ALS in the general public?
A: This remains an unanswered question as it is difficult to make direct comparisons among the studies addressing the question of ALS and the military. Each study is designed differently. Further investigation needs to be done in larger, population based studies.
Q: What about the lower risk for the cohort born after 1939, how does that compare with the risk reported for the Gulf War veterans?
A: It is difficult to effectively compare the two studies since methods such as age-adjusted incidence rates, were not used in both studies.
Q: Will people with ALS who are military veterans be eligible for Veteran Affairs benefits?
A: This is a logical question to ask, but has not been formally addressed to date by the Department of Veterans Affairs.
Q: What further research is being done to find out specifically what factors related to military service are associated with developing ALS?
A: The VA ALS registry has as one of its aims, attempting to answer this important question. Beyond the registry, we need expanded efforts to investigate military-specific exposures and job training activities that might be associated with ALS. This will require a large study focused specifically on this issue.
Q: Is exercise a risk factor for the development of ALS or not?
A: We don't yet know for certain if there is a link between exercise and the development of ALS. There have been several studies over many years looking for a possible association between exercise or athletic activities and ALS. While some of the study results have suggested a possible association between exercise or athleticism and ALS, others did not. Differences between the groups of patients studied and the ways in which the various studies were conducted may account for the lack of consistent data on this question. More research is needed to conclusively confirm whether or not there is an association between developing ALS and excessive exercise or athletics, and what the nature of the association might be.
