Individuals who live at higher altitudes may have a 50% lower risk of dying of Alzheimer's disease (AD) compared with their counterparts living at lower altitudes, say US researchers in findings that may point to a number of potentially associated factors.
In an analysis of deaths from AD over a 1-year period in Californian counties, the investigators found that people living at the highest altitudes were approximately half as likely to die from AD as those living at the lowest altitudes.
"This analysis suggests that altitude of residence may impact the risk for dying of Alzheimer dementia," the investigators, led by Stephen Thielke, MD, Geriatric Research, Education, and Clinical Center, Puget Sound VA Medical Center, in Seattle, Washington, write.
Although acknowledging that the findings should be interpreted "cautiously," the researchers note that "altitude of residence might be associated with environmental, lifestyle, or health- related factors, which influence dementia rates. Oxygen levels might have direct long-term effects on brain physiology."
The research was published online October 21 in JAMA Psychiatry.
Significant Reduction in Mortality
Previous investigations have indicated that there is a lower incidence of conditions such as attention-deficit/hyperactivity disorder at higher altitudes.
For the current study, the researchers examined county-specific AD deaths reported for 2005 by the California Department of Public Health.
Mean altitudes of inhabited areas were computed from US Board on Geographical Names data; crude mortality rates were calculated on the basis of the number of deaths attributed to AD per 100,000 inhabitants aged 65 years and older in each county.
The 2010 US Census was used to obtained socioeconomic data, and associations between mortality rates and the log of altitude were determined, taking into account age, sex, race/ethnicity, education, and average income for each county.
To compensate for inconsistencies in the reporting of dementia-related mortality, the team used data pertaining to at all counties as well as to only those counties that reported more than 15 dementia deaths.
In fully adjusted analyses, a doubling in altitude was associated with a 2.01-point reduction in the age-adjusted mortality rate for dementia (P = .01).
The results were similar after restricting the analysis to counties with more than 15 deaths due to AD, at a 2.21-point reduction (P = .03).
For the county at highest altitude, 1800 m above sea level, the predicted AD mortality rate was 14 points lower than that seen in the county at lowest altitude, 15 m above sea level, representing reduction in mortality rates of approximately 50%.
Not Evidence of Causation
Commenting on the findings, James Hendrix, PhD, director of global science initiatives at the Alzheimer's Association, believes that if the link between altitude is borne out in further studies, it could be one of several environmental factors linked to AD, including exercise and diet.
"[The investigators] were trying to see if they could correlate altitude because of some previous work done on hypoxia and neurodegeneration in rats, and see if that experimental result could be validated in a real-world setting," Dr Hendrix told Medscape Medical News.
"It could be that maybe if you live at high altitude, you're living in a more rural environment. Maybe you're getting more exercise and more opportunity to stay physically fit than if you were in an urban or suburban environment. That's why it's a pretty difficult thing to look at a paper like this and to draw a direct line between one factor and a result.
"For me, the bottom line is, it's probably too early to start recommending people move to high altitude if they're worried about Alzheimer's, but it certainly does speak to the need for more research," he said.
Dr Hendrix added that it should be borne in mind that the findings represent an association, not evidence of causation.
"It's also important to recognize that they don't really look at where people lived for years of their life. They're looking at where they die, and it's a challenging thing to know if someone maybe lived at high altitude for many, many years and then moved to a coastal community at the end of their life. So we don't really know that."
Need for More Research
Another concern raised by Dr Hendrix is that some of the counties discussed in the article did not report many AD deaths, with one county reporting no deaths. He noted that AD is underreported in the United States and that roughly half of people with the disease are never told that they have it.
"Just in the United States, we have 5.3 million Americans that are dealing with Alzheimer's disease. Without a cure or treatment, this disease will grow to 15.5 million by 2050, and so we really need to get some better understanding of the disease in ways to lower risk, and to treat it and help the way to many families that are touched by this horrible disease," he said.
"In the US, we're constantly pushing for more research through the NIH [National Institutes of Health], and right now the NIH funding, we believe, is less than half of what we really need to tackle this disease," Dr Hendrix concluded.
"We're less than a billion dollars a year right now, and we think we need to be up at the same level as other major diseases like cancer and heart disease.
"We think a $2-billion-a-year investment over 10 years is the only way we're going to get to a potential treatment or cure within the next 10 years, so that's what we're shooting for, and that's what we're hoping for."
The authors and Dr Hendrix report no relevant financial relationships.
JAMA Psychiatry. Published online October 20, 2015. Abstract
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Cite this: High-Altitude Living Linked to Lower Alzheimer's Risk - Medscape - Oct 29, 2015.