A related question about the aluminum that I haven’t seen addressed — All of the examples of amounts in daily life include casual exposures or ingestion — not injection. Is there a difference in how the body might respond to injected aluminum, versus aluminum passing through the gut?
Thanks for this question — it’s a good one, and a complicated one to answer! Sorry it took us some time to get back to you. Generally speaking, the answer is yes and no — how the body processes/responds to something depends a lot on how much gets into the bloodstream, because once it’s there, it will be handled the same, regardless of where it started out. Depending on the route of administration (like injection versus ingestion) the amount that makes it to the bloodstream can differ.
First, some basics about aluminum and aluminum in vaccines (which you may already know). Aluminum is a very abundant element, and is found in soil, plants, some foods, water, cows milk, breast milk, baby formula, etc. Not all vaccines contain aluminum, but the ones that do, contain aluminum not in the heavy metal form, but in the form of a salt, like aluminum hydroxide, aluminum phosphate, or potassium aluminum sulfate (which is called alum). These components, called adjuvants, are added to a vaccine to stimulate a stronger immune response; they can help ‘recruit’ immune cells to the site of injection and make the vaccine more effective. They’ve been used safely in vaccines for more than 60 years.
It’s important to note that aluminum salts are not ‘bioavailable’ – which means that they cannot be taken up directly by cells. Or in other words, there’s no point in keeping it around, because our body cannot make use of it, and so it gets excreted (more on that in a moment). While we are being exposed to and consuming aluminum constantly throughout our life, the vast majority of that aluminum is ingested, digested and then excreted by the kidneys. Very little is maintained in the body. But you’re right — the aluminum in vaccines is injected, not ingested. Does this matter? Well, not all of the aluminum contained in vaccines makes it into our bloodstream right away, but most of it does. Once there, the aluminum gets bound to carrier proteins, taken to the kidneys, and excreted. Only a very tiny amount is retained in the tissues of the body. This amount will decrease over time. Is this problematic? Well, this is where the bioavailable part comes in. The aluminum that may remain in the muscle tissue isn’t absorbed by cells, and researchers don’t have any evidence to suggest that there’s any risk that the quantity or the duration of the aluminum could be harmful.
Speaking of research, there has been a lot of research on this topic, as parents have expressed concern over aluminum adjuvants, and the medical and public health communities are always doing their best to make sure the vaccines we use are as safe and as effective as possible. A large review conducted in 2011 studied this particular issue very carefully. They wanted to know if the amount of aluminum infants are exposed to in the current immunization schedule could be problematic once added on top of the aluminum present at birth and acquired through breastfeeding/formula, food and the environment. They used the best methods currently available to measure how aluminum is absorbed, processed and secreted, the timing of immunizations in the recommended schedule, and the known amount of aluminum in vaccines. They found that the amount infants are exposed to is well below the lower limit of what they think could be harmful, even for low birth weight babies.
It’s important to say that there is such as thing as aluminum toxicosis in humans, but it happens exclusively in people with severe kidney disease who are being given intravenous medicines with very high aluminum content, or in those exposed to extremely high levels of aluminum via their occupation. The amount in vaccines and food doesn’t come anywhere close to that.
So — what does this mean for your question? There is truth to the idea that compounds ingested vs. those that are injected might be handled differently by the body, and in some ways, this is true for aluminum in vaccines. However, what matters is this: 1) the vast majority of aluminum in vaccines makes it to the bloodstream quickly and is excreted within hours; 2)What amount may remain in tissues will also be processed and excreted within days, but we don’t have evidence to support that this is harmful; 3) The amount of cumulative aluminum exposure (food+ environment + vaccines) does not cross the threshold of what we know to be dangerous, even for the smallest infants. Hopefully this is helpful!