I've seen friends fret over the purported link between aluminum and Alzheimer's disease and have often wondered if their fears are founded on fact. Should they give up aluminum pans or aluminum-containing antiperspirants? I've always heard that aluminum's health dangers are just hype. So what's the real deal?
The connection between aluminum and Alzheimer's disease is less a myth than a long-standing scientific controversy. It began in 1965, when researchers discovered that injecting rabbits' brains with aluminum caused them to develop neurofibrillary tangles, the twisted proteins found in brain cells of patients with Alzheimer's disease, a degenerative brain disorder that destroys memory and cognition.
The finding spurred a rush of research. Just eight years later, a Canadian group studying brain tissue from deceased Alzheimer's patients found that certain parts of their brains had two to three times more aluminum than a normal brain. By 1980, Daniel Perl and Arnold Brody had managed to actually peer inside human tangle-bearing brain cells -- and found aluminum there, too.
"That really changed the whole complexion of the thing," recalls Perl, now a professor of pathology in the Uniformed Services University of the Health Sciences in Bethesda, Md. "I was getting called all the time, because there was so much public interest."
Despite the rise in interest, no one could figure out what this meant for human health. Part of the problem was that scientific techniques were -- and still are -- too imperfect to provide an answer. Whether they were studying brain cells or conducting population-wide epidemiological studies that tracked aluminum exposure and Alzheimer's risk, researchers lacked the tools to get very precise or conclusive results.
"Aluminum is so common, so prevalent in the environment, that studying it is a hard task," says John Savory, a professor emeritus of pathology at the University of Virginia who helped discover that aluminum exposure can cause neurological and dementia-like symptoms in dialysis patients. "Just a speck of dust can contaminate your sample, because it's everywhere."
Naturally occurring aluminum is the third-most-abundant element on Earth, so it really is everywhere. Because it's present in the soil, it can be found in certain foods, such as spinach and tea. It's also used in a number of industrial processes that bring it into close contact with humans. Although many studies of aluminum exposure have focused on drinking water -- utilities often use aluminum salts to clarify and purify their water -- it is also found in cookware and food packaging, in antacids, antiperspirants and a handful of medications, and in some processed foods. That makes teasing out people's exposures to aluminum over a lifetime, and the effect of those exposures, "very hard to do," Perl says.
It's no surprise, then, that 30 years of studies on the aluminum-Alzheimer's link have yielded conflicting results.
For example, a 1997 study of nearly 1,000 men from England and Wales found little association between their Alzheimer's disease incidence and their estimated exposure to aluminum through drinking water, but a 15-year study that followed 1,925 French men and women concluded that high aluminum consumption from drinking water might be a risk factor for Alzheimer's disease. In a 2003 World Health Organization survey of six high-quality epidemiological studies of aluminum in drinking water as a risk factor for Alzheimer's disease, three found a positive association, while three did not.
These differing results are due to the difficulties inherent in epidemiological studies, which require researchers to rely on potentially inaccurate records and to follow people over long periods, says Amy Borenstein, a professor of epidemiology at the University of South Florida College of Public Health.
Borenstein studied Alzheimer's disease risk and aluminum exposure through antiperspirants and cookware more than 20 years ago, also with unclear results. "We do the best we can," she says. "Studying humans is hard."
Another problem is that the topic simply fell out of favor. As Alzheimer's disease researchers pursued more easily testable avenues for understanding the disease, such as its genetic risk factors and its formation of brain plaques (instead of the tangles), aluminum fell by the wayside, Savory says.
"It became very, very difficult to get funding to work on aluminum. As soon as you mentioned aluminum, you're dismissed with 'Oh, that hypothesis was disproven years ago,'" Savory says."But it has not been disproven. The truth is, nobody knows."
Perl also met with difficulty in funding his aluminum research, and he eventually shifted his efforts to the link between trauma and neurodegenerative diseases. Although he doesn't -- and never did -- believe that aluminum causes Alzheimer's disease, he says that it may be involved somehow in the disease's progression and that not investigating this may put Alzheimer's research at a disadvantage.
"We don't know what causes diabetes, for example, but we can treat it," Perl says. "So just because something isn't the ... direct cause of a disease doesn't mean it's not important."
But Borenstein believes aluminum's contribution to Alzheimer's risk is too small to warrant a lot of research. "If aluminum plays any role, it's very small," she says. "And there are many other, much more important risk factors to study."
These other factors include genes as well as metabolic and vascular disease -- things such as diabetes and heart disease -- that studies have shown are strongly associated with Alzheimer's disease; level of intellectual stimulation and educational attainment; and social engagement. These factors may one day help researchers treat and even prevent the disease, Borenstein says.
So where does this leave a concerned consumer? You can try to limit your aluminum consumption by choosing aluminum-free products, Perl says, "but we don't really understand enough about (aluminum's possible association with Alzheimer's disease) to make good recommendations."
For what it's worth, Perl and Borenstein haven't replaced their cookware, changed their antiperspirants or given up using aluminum foil. Savory hasn't, either, though he does make a point of drinking water only from his own well, which he says contains considerably lower levels of aluminum than his town's water supply.
Avoiding all aluminum isn't possible, because the metal is so ubiquitous. If Alzheimer's is your worry, you're better off making sure to keep your mind active and your heart healthy, Borenstein says. In the long run, these steps will do far more to protect your brain.