Part of the anti-vaccinationist stance against immunization is the belief that vaccines contain harmful chemicals such as aluminum, formaldehyde and thimerosal. Although mercury-based thimerosal is no longer used in any U.S. vaccines except certain flu shots, and the amount of formaldehyde is a tiny fraction of that found in many foods – including those fed to babies such as pureed bananas or pears – aluminum remains a villain among the anti-vax crowd. But, as with the discredited link between the measles vaccine and autism discussed in a previous post, no medical evidence exists to support the aluminum hypothesis.
Aluminum salts are employed as powerful adjuvants to enhance the immune system response to a vaccine, thus reducing the number of repeat injections needed. What anti-vaccinationists fail to understand, however, is that less than 1% of aluminum in vaccines is actually absorbed by the body. The same is true of the aluminum found in our food supply, in drinking water and even in the air we breathe, as well as the breast milk or infant formula ingested by babies. For vaccination, the daily quantity of aluminum absorbed by a vaccinated newborn infant is 10 times smaller than the FDA’s threshold for neurotoxicity.
Because it has been suggested that aluminum could be linked to certain neurological disorders such as Alzheimer’s Disease, anti-vaccinationists maintain that injected aluminum rapidly enters the bloodstream and thereby accumulates in the brain, causing neurological damage – reminiscent of Wakefield’s fraudulent claim about autism. There are several scientific fallacies underlying this assertion, however.
The first fallacy is that injected aluminum finds its way into the body more rapidly than ingested aluminum. In fact, most of the aluminum adjuvant in a vaccine remains near the injection site for a long period and is only absorbed slowly into the bloodstream, at approximately the same daily rate as ingested aluminum. Even though the amount of ingested aluminum is much larger, most of that is absorbed in the intestines and only released slowly into the blood.
Another fallacy involves the neurotoxicity of aluminum in the brain. Although aluminum and other chemicals can enter the brain from the bloodstream, they first have to penetrate a protective semipermeable membrane that separates flowing blood from brain tissue, known as the blood brain barrier. The blood brain barrier normally keeps circulating pathogens and toxins from getting into the brain, while allowing the passage of water, nutrients and hormones.
The flawed claim is that injected aluminum sneaks its way into the brain by hiding in macrophages – a type of first-responder white blood cell that devours germs, cellular debris and foreign particles, and plays an important role in the body’s immune system. Unable to digest metals, say anti-vaccinationists, the aluminum-loaded macrophages travel to the brain via the blood or lymphatic system. If the brain is already inflamed, the macrophages can cross the blood brain barrier and unload aluminum inside the brain. The aluminum supposedly causes further inflammation, leading to autism and other neurological disorders.
But none of this makes sense to many doctors and scientists who work in immunology or neuroscience. A neurovascular biologist who’s an expert on the blood brain barrier faults the science in several of the papers behind the Trojan-horse macrophage hypothesis. And he calls out the claim in one paper that macrophages digest injected aluminum as “not only exaggerated … but also provocative and fraudulent,” though this criticism was later accepted as justified on a major anti-vaccinationist website.
The website, whose authors prefer to remain anonymous, claims to be science-based and guided only by scientific evidence – the same as the emphasis of the present blog. The site also attempts to defend itself against charges of cherry picking research papers supporting its position that aluminum adjuvants cause autism. But it merely lists just the abstracts of a handful of the many papers backing the emerging consensus that autism is caused by maternal exposure to infections or toxins during pregnancy.
In any case, even if the aluminum hypothesis were correct, the fact that the amount of aluminum absorbed from vaccines is comparable to the amount absorbed from aluminum ingested by the body means that macrophages could sweep up swallowed aluminum just as easily as injected aluminum. There’s no good evidence that either occurs, although the mechanisms by which adjuvants act are still not fully understood.
Hat tip: Mike @realiwasframed
Next week: Politics Clashes with Science over Glyphosate and Cancer