When it comes to medical products, there is an even greater uncertainty around the ingredients. Not only do the problems above come into play, but add on distrust of faceless companies or unsavory associations, and the fear increases. I illustrated this in two of my previous posts, one on formaldehyde and one on monosodium glutamate. Some vaccines contain small amounts of these substances as a part of the manufacturing process. But there is a vaccine ingredient that gets even more bad press than either of those: aluminum (or aluminium, if you prefer). Let's take a look at this substance, how we're exposed, how our bodies deal with it, and its role in vaccines.
What is Aluminum?
|Aluminum Hydroxide Crystal|
Image credit: Ben Mills
Concerns about how aluminum affects health arose in the 1960s and 1970s, when it was thought that there may be a link between Alzheimer's disease and exposure to large amounts of aluminum (subsequent research has largely discredited this idea among scientists, yet it persists among fringe scientists and in public opinion). Similarly, anti-vaccine activists blame the aluminum used as adjuvants in vaccines as a cause of autism. Aluminum is neurotoxic at high levels of exposure, such as among patients with renal dysfunction who are undergoing dialysis with an aluminum-containing dialysate, but it takes a lot of aluminum to cause neurological effects. Even then, its effects are not identical to the symptoms of Alzheimer's disease or autism.
How Are We Exposed?
As noted above, aluminum is everywhere. Natural processes, like volcanic eruptions and weathering of rocks release it into the environment, as do human activities like mining, production of aluminum metal and alloys, and coal-burning power plants. Every time you breathe, you take in tiny amounts of aluminum. It's also in the water that we drink, at concentrations of about 0.1 mg/L of water or less. But by far, the most common way we are exposed to it is in the food that we eat. It is in vegetables and unprocessed foods at low concentrations (e.g., <0.15 mg/kg in eggs, apples, cabbage and potatoes) and at higher concentrations in cereals, fish and dairy products. Even newborn infants take in aluminum from breast milk. According to the Agency for Toxic Substances and Disease Registry:
Based on the FDA’s 1993 Total Diet Study dietary exposure model and the 1987–1988 U.S. Department of Agriculture (USDA) Nationwide Food Consumption Survey, the authors estimated daily aluminum intakes of 0.10 mg Al/kg/day for 6–11-month-old infants; 0.30–0.35 mg Al/kg/day for 2–6-year-old children; 0.11 mg Al/kg/day for 10-yearold children; 0.15–0.18 mg Al/kg/day for 14–16-year-old males and females; and 0.10–0.12 mg Al/kg/day for adult (25–30- and 70+-year-old) males and females.
|Source: Stahl et al. (2011).|
Click to enlarge.
In the end, the total body burden of aluminum in an average person is around 30-50 mg.
Role In Metabolism
Humans do not appear to use aluminum for any biological function. But that's not to say that our bodies have no mechanism for dealing with it. If we didn't, humans would have died off long ago. At birth, it is estimated that infants already have a total body burden of aluminum of about 384 µg. Over the first six months or so of life, levels remain relatively stable, as the overall aluminum content of breast milk is relatively low <1% is taking up via the gut. When a child transitions to solid foods, the rate of aluminum uptake increases.
|Source: Mitkus et al (2011).|
Click to enlarge.
When aluminum exposure occurs via injection, about 60% of the substance is eliminated in the urine within the first day. After about five days, nearly three-quarters of the aluminum is excreted in the urine, with a small amount in the feces. The remaining aluminum is retained in the bone, lungs, kidney, spleen, liver, heart, lymph nodes and brain (in decreasing order of concentration), slowly being excreted from the body over the course of months to years.
How Much Is Too Much?
Much of the toxicity data on aluminum in humans comes from studies of workers exposed to aluminum while on the job or from patients with renal dysfunction. We also get information from numerous animal studies. Aluminum has not been observed to cause death in humans, though animal studies do provide us with an idea of how much it would take to be fatal to rodents. In mice, it takes daily ingestion of about 200 mg Al/kg/day to cause death. That would be equivalent to a human 3.2 kg newborn ingesting 640 mg of aluminum every day for days to weeks. In cases of individuals using aluminum-containing antacids (which contain 300-600 mg Al per dose) on a long-term basis, as well as among patients undergoing dialysis with an aluminum-containing dialysate, osteomalacia (aka rickets, or softening of the bones) has been observed, though this does not appear to be a problem among healthy individuals who do not have elevated aluminum exposure.
As noted before, aluminum is neurotoxic at very high doses. Whereas healthy individuals can safely consume hundreds of milligrams of aluminum every day without any neurological effects, people with renal dysfunction who undergo prolonged dialysis with aluminum-containing dialysates are at risk for severe, and potentially fatal, complications. In those cases, patients develop what is called "dialysis dementia". Symptoms can include confusion, speech disorders, motor difficulties, and seizures. Dialysis dementia could also lead to coma and even death. The important thing to keep in mind about these neurological effects is that they have only been documented after prolonged, high levels of aluminum exposure in those with renal dysfunction, and primarily when it is injected intravenously, directly into the bloodstream (not orally, not inhaled, not intramuscularly, not subcutaneously). Exposure to normal, everyday levels of aluminum have not been linked to neurotoxicity.
What About Vaccines?
So how much aluminum is in vaccines? Why is it even used?
Some vaccines only use parts of bacteria or viruses, rather than the whole thing. Because of this, large amounts of those parts are required to generate an immune response strong enough to produce immunity. That is, unless an adjuvant is used. An adjuvant is something that is added to a vaccine to boost the immune response, meaning that less of the antigens (those bits and pieces of bacteria and viruses) is required. In adjuvanted vaccines, the antigens are essentially stuck onto aluminum hydroxide or aluminum phosphate (aluminum salts). The aluminum salt serves a few primary roles. First, it gets the immune system's attention. First-responder phagocytes at the injection site will binge on some of the aluminum until they die from overeating, releasing particles that signal cell damage. The next line of phagocytes encounter all of this and are more likely to signal an inflammatory response, recruiting immune cells to find out what's going on. Second, because it is not very soluble, the aluminum salt stays put at the injections site for a while, preventing the antigens from being swept off into the bloodstream and diluted through the body. Keeping the antigens localized gives the immune system more time to investigate and get to know the antigens so that the next time you're exposed, your immune system knows what to do and how best to respond in order to keep you from getting sick. Finally, although not related to its adjuvant activity, it helps stabilize the vaccine and prevent the antigens from precipitating out of solution and sticking to the side of the container. (Sorry about anthropomorphizing the antigens, but sometimes you just have to.) Using an adjuvant like aluminum hydroxide means that less antigen is needed to produce an immune response. That means a reduction in the side effects caused by the antigen and the ability to produce more doses of vaccine without needing to increase antigen production.
The biggest concern about the use of aluminum-based adjuvants is safety. If aluminum is neurotoxic at high, chronic levels of exposure, does that mean it is also neurotoxic at the amounts found in vaccines? The short answer is no. Aluminum salts have been used in vaccines for about 70-80 years. Aluminum adjuvant is not used in any "live" vaccine (MMR, varicella, rotavirus), inactivated polio vaccine (IPV), nor in any influenza vaccine in the U.S. It is used in the following vaccines:
|Source: Vaccine Education Center,|
Children's Hospital of Philadelphia
While aluminum vaccine adjuvants do not cause neurological complications, they can cause local adverse reactions. The most common effect is pain and swelling at the injection site. This is generally mild and resolves quickly. In rare cases, it may also result in an allergic reaction to the aluminum and contact dermatitis.
Aluminum-based adjuvants in vaccines have been in use for about 80 years, with millions upon millions of doses given. Despite so many years of safe use of these adjuvants, some people still fear them. They imagine that the tiny amounts of aluminum in some vaccines cause serious neurological side effects despite there being no scientific evidence to support that belief. As with other vaccine ingredients, the fear is out of proportion, ignoring the old adage that the dose makes the poison. At low doses, aluminum is very effective at stimulating an immune response to increase the effectiveness of vaccines. We are also exposed to, and take in, aluminum every day. We breathe it in; we drink it; we eat it. At any one time, we have around 30-50 mg of aluminum in our bodies, many times more than is found in any vaccine. At worst, we face local reactions when we get an aluminum-containing vaccine.
While aluminum is an effective adjuvant with a long history of safety, it is becoming an outdated technology. As new vaccines are developed, we are going to need new adjuvants that will work with novel vaccine formulations. Viable alternatives to aluminum-based adjuvants may also go a ways toward addressing some of the fears that cause some people to forgo vaccination. But while those new methods of increasing the effectiveness of immunizations wend their way through the slow, rigorous process to approval, we need to view aluminum in vaccines as what it is: a safe and effective means of increasing the effectiveness of our vaccines.
1kg = 1,000g = 1,000,000mg = 1,000,000,000μg
Here are some real-world examples of those weights (technically masses):
1kg = a 1L bottle of soda
1g = a paper clip
1mg = a very, very small snowflake
1μg = take your paper clip, cut it into a million pieces and take one of those
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