Dr. Amy Tuteur is an obstetrician-gynecologist. She received her undergraduate degree from Harvard College and her medical degree from Boston University School of Medicine. Dr. Tuteur is a former clinical instructor at Harvard Medical School.

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OCTOBER 29, 2009 7:11AM

The truth about thimerosal

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Vaccinations have been around for over 200 years and vaccine rejectionists have been around for nearly that long. Over the years, the basis for claims of harm from vaccines have changed, but one factor has remained constant. Vaccine rejectionists have never been right. The current fear mongering surrounding thimerosal is just the latest iteration in an ongoing effort. That fear mongering rests on two factors, ignorance of basic chemistry and ignorance of the existing research on thimerosal.

To hear vaccine rejectionists tell it, all mercury containing compounds are dangerous and therefore thimerosal is dangerous. But that’s not how chemistry works. The toxicity of a substance depends on how atoms are arranged, not simply which atoms are present. The fact that some mercury compounds are dangerous does not mean that thimerosal must be dangerous because it contains mercury.

Consider the example of sodium. Sodium is both poisonous and explosive. That does not mean that compounds that contain sodium are either poisonous or explosive. Table salt (sodium chloride) contains sodium, yet we do not worry that salting our food will result in an explosion at the dinner table.

Similarly, mercury is poisonous, but that does not mean that any compound that contains mercury is also poisonous. Some mercury containing compounds, like methyl mercury, are poisonous. Methyl mercury is the found in fish and is the reason why restrictions of fish consumption are recommended for certain groups. Thimerosal is ethyl mercury and is not poisonous.

Though methyl mercury and ethyl mercury might sound like they are very similar, one is poisonous and the other is not. How can that be? Consider the case of alcohol. Methyl alcohol (methanol), also known as wood alcohol, will lead to blindness or death if you drink it. Ethyl alcohol (ethanol) is the alcohol found in wine and spirits. Chemical structure is more important than the identity of the individual atoms that make up the compound.

The safety of thimerosal is more than simply theoretical. Contrary to the claims of vaccine rejectionists, thimerosal has been studied extensively in large populations. There have been many studies that demonstrate the safety of thimerosal.

Consider the study Thimerosal exposure in infants and developmental disorders: a retrospective cohort study in the United Kingdom does not support a causal association (Andrews et al. Pediatrics 114. 584-591.2004). This was a retrospective cohort study was performed of 109 863 children who received thimerosal containing DPT vaccines. The study found no evidence that thimerosal caused developmental delays.

Thimerosal exposure in infants and developmental disorders: a prospective cohort study in the United kingdom does not support a causal association (Heron et al. Pediatrics 114. 577-583.2004) followed 14,000 children for up to 7+ years. The authors found:

Contrary to expectation, it was common for the unadjusted results to suggest a beneficial effect of thimerosal exposure. For example, exposure at 3 months was inversely associated with hyperactivity and conduct problems at 47 months; motor development at 6 months and at 30 months; difficulties with sounds at 81 months; and speech therapy, special needs, and "statementing" at 91 months… CONCLUSIONS: We could find no convincing evidence that early exposure to thimerosal had any deleterious effect on neurologic or psychological outcome.
The bottom line is that the vaccine rejectionists are wrong once again. The fact that thimerosal contains mercury does not mean it is dangerous because the chemical structure determines the danger, not the identity of the individual atoms. More importantly, thimerosal has been studied extensively in large populations over time and has been demonstrated repeatedly to be safe.

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They also reject the FluMist vaccine, which doesn't appear to contain any thimerosal at all.
"They also reject the FluMist vaccine, which doesn't appear to contain any thimerosal at all."

In that case, they're freaked out because FluMist contains live attentuated (weakened) virus.

Vaccine rejectionists are constantly moving the goalposts, in any case. "Thimerosal is harmful." "Oh, it's not? Then aluminum is harmful." "Oh, it's found in the environment? Well then, x (insert your favorite substance) is harmful."
Americans seem to think that if they follow some prescribed course of "virtuous" action they will never die. Can we all say "Magical Thinking"?
Thank you! Rated. As a former chemistry major, this issue has been driving me nuts! Anyone who doesn't want to get vaccinated should read The Great Influenza.

The other side....

"Can we all say "Magical Thinking"?

And magical thinking is very seductive.

"As a former chemistry major, this issue has been driving me nuts!"

This is a point that I try to highlight over and over again. Anyone who actually knows something about chemistry, statistics, immunology or virology knows that vaccine rejectionism is a manifestation of ignorance about the relevant subject, not the result of being "educated."

You don't seem to understand that youtube videos and screeds from websites for lay people are undermining your credibility even further.
Amy, as lordgarion has already asked you several times (to which you have yet to answer), would you inject only ethyl mercury (not ethyl mercury that is contained within a vaccine) into your loved ones, just to "prove" how safe it is? If not, then why... if it's so "safe".

Also, please explain why ethyl mercury is included in some vaccines.
While many studies show that thimerosal to be "relatively safe," and minimal correlation to adverse side effects like Autism there is some evidence to support negative effects from neonatal exposure.

I don't object to vaccination, but almost any vaccine today can be received thimerosal free. If it makes parents more open to vaccination, and provides the same result, why chance it ?
The Wanderer:


The study mainly showed that increased levels of mercury were associated with BETTER performance.
" Higher prenatal mercury exposure was associated with better performance on one measure of language and poorer performance on one measure of attention and executive functioning. Increasing levels of mercury exposure from birth to 7 months were associated with better performance on one measure of fine motor coordination and on one measure of attention and executive functioning."

In other words, mercury levels had basically no effect on anything.
Thank you for the study links, I will read them and "other studies that linked to this article" soon.
I am seriously grumpy about this whole topic (that’s down from outraged, which I suppose is an improvement.) While I chafe at the disrespect apparent in your writing, Amy, I will credit you with citing as much truly germane research as I've even seen in any thimerosal-defending article.

I cannot tell you how many articles I have read that purported to discuss thimerosal and went on to cite nothing but studies about the safety of vaccinations in general, and to have such a dismissive, arrogant, professionally defensive tone that I could not believe the writer had come to the topic with an objective, scientific attitude.

It does not help your case when you and other thimerosal promoters carelessly lump all who are concerned about the safety of the compounds injected into children into a big pile of superstitious, know-nothing "vaccination rejectionists." Like many other parents, I have no problem with vaccinations per se or with attentuated virus. It's the widespread use of relatively untested additives that concerns me.

I was formerly a ‘faith-based’ vaccine consumer who dismissed those who resisted vaccinations as kooks. Then, as a mother of a son with autism who received his thimerosal injections in the early 1990s, I was outraged when I learned of the dearth of studies that had been done on thimerosal and young children BEFORE the pharmaceutical manufacturers starting injecting it into millions of children.

The fact that studies have SINCE proven thimerosal safe for babies and small children does not change the fact that millions of children were injected before those studies.

Thank you for the very real information directly on the topic of thimerosal—as opposed to vaccinations in general. Now I'm going to go looking for information that might give me faith in the current-day process of studying and approving compounds BEFORE they are injected into millions of babies and toddlers

Thank you for your thoughtful comment. Unfortunately it contains a glaring error, an error that has been disseminated by vaccine rejectionists.

"I was outraged when I learned of the dearth of studies that had been done on thimerosal and young children BEFORE the pharmaceutical manufacturers starting injecting it into millions of children. "

Thimerosal was first studied in animals and then in humans in 1931! It was added to vaccines in the 1930's in response to a series of deaths in children who received vaccine contaminated with bacteria in the late 1920's. It has undoubtedly save thousands of lives.

Thiomerosal has been in widespread use for 70 years and we have excellent data about its safety.

This illustrates one of the central public relations problems regarding vaccine rejectionism. Scientists had no reason to believe that thimerosal cause autism or anything else, but when parents were hesitating to vaccinate their children, large scale studies specifically devoted to uncovering any link between thimerosal and autism were undertaken. The thinking was that large scale studies would convince parents that thimerosal is safe.

Unfortunately, the studies had the opposite effect. For many vaccine rejectionists the fact that scientists were studying the link that they had essentially made up out of thin air seemed to them to be "proof" that thimerosal was dangerous.

Then, compounding the public relations error, governments decided to mandate the removal of thimerosal. Again, no one with any actual knowledge of thimerosal and immunology believed that thimerosal was dangerous. The thinking was that removal of thimerosal would finally reassure parents.

Once again the effect was perverse. Vaccine rejectionists viewed the removal of thimerosal as "proof" that thimerosal was recognized as dangerous. Nothing could be further from the truth.

Clearly you have made good faith efforts to investigate vaccination. Yet, even a thoughtful person such as yourself unwittingly believed and repeated an absolute lie. Thimerosal was thoroughly tested 70 years ago, yet you didn't know that.

Perhaps this example will help people understand that we are fighting against a pernicious campaign of deliberate lies. If parents want to get angry at anyone, they should be angry at vaccine rejectionists who have led people to risk their children's very lives by disseminating ignorance and lies.
"This is a point that I try to highlight over and over again. Anyone who actually knows something about chemistry, statistics, immunology or virology knows that vaccine rejectionism is a manifestation of ignorance about the relevant subject, not the result of being "educated."

How about this statistic for ya.....since you like those so much. From the CDC.

The 15 leading causes of death in 2006 were:
Diseases of heart (heart disease)
Malignant neoplasms (cancer)
Cerebrovascular diseases (stroke)
Chronic lower respiratory diseases
Accidents (unintentional injuries)
Diabetes mellitus (diabetes)
Alzheimer’s disease
Influenza and pneumonia
Nephritis, nephrotic syndrome and nephrosis (kidney disease)
Intentional self-harm (suicide)
Chronic liver disease and cirrhosis
Essential hypertension and hypertensive renal disease (hypertension)
Parkinson’s disease
Assault (homicide)

Now notice #8 on our list here.....8 Influenza and pneumonia .............. (J10–J18) 56,326 deaths. Now, we ALL know that 36,000 people die from the flu each year....that's what they harp about all the time on the news and they have been using that figure for years now. So that means there's been 26,326 deaths from pneumonia right? Ahhhh....but let us take a closer look the death totals shall we.

Influenza and pneumonia ..........(J10–J18) 56,326
Influenza ...................(J10–J11) 849
Pneumonia .................(J12–J18) 55,477

Nice little statictical mumbo jumbo no. Gosh, you take a look at the first example up above on page 5 of their repost and it sure looks like the flu is this big bad thing that you better run out and get a shot for huh. But get way down on page 42 of the report....and what do we see. Hmmmm....849 deaths total. Now Amy, it has been awhile since I went to school, but that doesn't look anywhere close to 36,000 to me. Kinda hard to get people whipped up into a panic about the flu if there's only 800+ people (mostly the elderly) dying from it now is there.

I think my credibility is doing just fine thank you very much. BTW...nice dodge of mine and the others questions, you're really building up your credibility with each post! Keep up the good work!! LOL
PS....that CDC report was from the year 2006....just fyi

This is like shooting fish in a barrel. It's too easy.

"849 deaths total. "

Virtually no one dies from the flu alone; they die from COMPLICATIONS of the flu. And what is the most common deadly complication? You guessed it: bacterial pneumonia.

People who might otherwise be able to fight off pneumonia sustain enough lung damage from the influenza virus that the bacteria can easily invade, take hold and kill them.

Prevent the flu and you save thousands of people from dying of pneumonia.
Dr. Amy,

At the time when each of our two children's immunization appointments came up, I grilled our pediatrician about vaccines, safety, whether they contained Thimerosal or not. I even requested and received the inserts (list of ingredients) that came with each vile. We have a good relationship and discussed the pros and cons of things like the Hep B shot given to newborns at the hospital and it is necessary, etc... He also has children the same age as ours so we have often compared notes from time to time on more basic stuff.

I agree that the data shows no correlation between the use of Thimerosal and Autism, at least from the articles that I have read. But I am wondering if you know of any studies that analyze the rate of reported cases of autism between the two populations, those who were vaccinated and those who weren't? Specifically, now that it seems we have a large data set available of non-vaccinated children, is there any difference by which the number of children receiving diagnoses on the Autism Spectrum is any less when compared to children who have been vaccinated on schedule? I think the findings would be very interesting.

I have read a good deal on the subject and I have often wondered if in some cases, some children with some genetic variance are more likely to develop autistic characteristics around the time they get their MMR shot.

I am also an armchair immunology enthusiast and my medical knowledge is rather limited, so I apologize if I missed something. Thank you for writing on this subject and I look forward to your response.

sara :)
You better learn how to fish better.....hate to break it to you, but the flu isn't the only way to get pneumonia, or did you miss that class?

What Causes Pneumonia?
There are about 30 different causes of pneumonia. However, they all fall into one of these categories:

Infective pneumonia: Inflammation and infection of the lungs and bronchial tubes that occurs when a bacteria (bacterial pneumonia) or virus (viral pneumonia) gets into the lungs and starts to reproduce.

Aspiration pneumonia: An inflammation of the lungs and bronchial tubes caused by inhaling vomit, mucous, or other bodily fluids. Aspiration pneumonia can also be caused by inhaling certain chemicals.

Infective Pneumonia
Bacterial pneumonia can attack anyone. The most common cause of bacterial pneumonia in adults is a bacteria called Streptococcus pneumoniae or Pneumococcus. Pneumococcal pneumonia occurs only in the lobar form.

An increasing number of viruses are being identified as the cause of respiratory infection. Half of all pneumonias are believed to be of viral origin. Most viral pneumonias are patchy and the body usually fights them off without help from medications or other treatments.

Pneumococcus can affect more than the lungs. The bacteria can also cause serious infections of the covering of the brain (meningitis), the bloodstream, and other parts of the body.

Nice To Know:

The viruses and bacteria that cause pneumonia are contagious and are usually found in fluid from the mouth or nose of an infected person. Pneumonia can spread by coughs and sneezes, by sharing drinking glasses and eating utensils with an infected person, and contact with used tissues or handkerchiefs.

Handwashing is important when around a person with pneumonia, since the bacteria and viruses can also be spread to your hands and then to your mouth.

Aspiration Pneumonia
Inhaling vomit, irritating fumes, or other substances can result in aspiration pneumonia. Agents such as petroleum solvents, dry cleaning fluid, lighter fluid, kerosene, gasoline, and liquid polishes and waxes are the most likely causes. Pulmonary edema, or fluids in the lung from injury, can develop rapidly. With repeated exposure, the lungs may lose elasticity and small airways may become obstructed. This can lead to increased reactive airway disease and chronic lung disease in adults.

Nice To Know:

Although most cases of pneumonia are caused by a viral or bacterial infection, the disease can also be caused anything that obstructs the bronchial tubes. Tumors, peanuts, hard candies, or small toys in the bronchial tubes can trap bacteria, viruses, or fungi, resulting in pneumonia.
Amy- BUT also detrimental.

"Higher mercury exposure during the first 28 days of life was associated with significantly poorer performance on the Goldman–Fristoe Test of Articulation, second edition (GFTA-2), and better performance on the Finger Tapping Dominant Hand test (Table 3). Among boys, higher neonatal mercury exposure was associated with significantly better performance on the Finger Tapping Dominant Hand test, the Finger Tapping Non-dominant Hand test, and performance IQ on the Wechsler Abbreviated Scale of Intelligence (WASI). Among girls, increased neonatal mercury exposure was associated with significantly lower scores in verbal IQ on the WASI and a lower likelihood of motor tics on the basis of ratings by parents."

As a health care consumer, I would hope health care providers provide options to their clients. As mandated in the state I live in, health care providers are required to provide a thimerosal free vaccine upon request. Let me be the first to say, I am definitely going to take them up on that option. When it comes to my child(ren), I prefer not to take unnecessary risks. You can do whatever you like with yours.
There are better ways to show that ethyl-Hg/thimerosal is not the cause of the ASD increase. Hg was removed from vaccines by 2002, to be conservative, except for the flu vaccine. So, we should see ASD symptoms start to regress back to the levels we saw before society began pumping babes up with way too many vaccines. But, we don't see that. We need a study, let me find one quickly, ok, here is an alright analysis. It is big, sweeping, imperfect but makes a nice graph.

Point is, we should be seeing ASD on the decline if Hg from vaccines is the causative agent.

I am not saying that the myriad vaccines the medical community foists on babes are not part of the cause of the mysterious rise in ASD, but, it looks like Hg is just not alone responsible.

Let us look back, everyone thought the polio vaccine was perfect, but then science found the virus SV40 was contaminating the vaccines, and SV40 (maybe) caused cancer. Yikes. At the time, science was using the best science...

So be wary of the best science, you never know what your gonna get.

"But I am wondering if you know of any studies that analyze the rate of reported cases of autism between the two populations, those who were vaccinated and those who weren't?"

There have been many large scale studies comparing autism rates in vaccinated and unvaccinated children. A classic study of that type is "A population-based study of MMR vaccination and autism" ( involving more than 500,000 Danish children. There was no difference in autism rates between vaccinated and unvaccinated children. In fact, if anything, vaccination appeared to be mildly protective against autism.
The Wander:

"When it comes to my child(ren), I prefer not to take unnecessary risks."

Evidently you do. Not vaccinating your children is very dangerous. Thimerosal is not dangerous at all.

"Let us look back, everyone thought the polio vaccine was perfect,"

No, no immunologist, virologist or pediatrician EVER thought ANY vaccine was perfect. That's yet another lie made up by vaccine rejectionists. All vaccines carry the risk of DEATH and the medical profession has been quite honest about that. That's what make accusations of a cover up particularly ludicrous.
Dr.Amy-I never once did I say I wouldn't get my children vaccinated, I do. I don't disagree with vaccination and benefits they provide either. I opt for a thimerosal free vaccine because they are available and I like that I have that option.
Dont forget to add your daily allowance of dental mercury exposure to your vaccine intake. The more the merrier!!!

Mercury's toxicity is related to the amount absorbed. The mercury absorbed from all sources accumulates in body organs and tissues, mostly in the kidneys, but also in the brain, lungs, liver and gastrointestinal tract.

Isn't Mercury Deadly?
Mercury vapour, methyl mercury and ethyl mercury all target the central nervous system and mercury vapour and ethyl mercury also target the kidneys. Inorganic (metallic) mercury primarily targets the kidneys and stomach.
The allowable or safe intake of mercury has recently been reduced to 0.1 microgram/day per kilogram of body weight.
There is concern, but no clear evidence, that mercury emitted from amalgam fillings may cause or worsen degenerative diseases such as ALS, Alzheimer's disease, multiple sclerosis, and Parkinson's disease.
It is important to realize that consuming just one 7 oz (198 grams) can of tuna per week translates into a mercury intake of 0.1 microgram/day of mercury per kilogram of body weight – equivalent to the currently recommended maximum daily intake.
How Dangerous are Amalgam Fillings?
Doctors and researchers point to incontrovertible evidence that mercury continually leaches from amalgam fillings at a rate of about 10-50 times the safe limit (0.28 microgram/day) set by the US Public Health Service.

Several studies have found that chewing markedly increases the amount of mercury released from amalgam fillings into the mouth and that these mercury vapours easily find their way into the pituitary gland and the brain.

Autopsies performed at the Karolinska Institute in Sweden revealed that people with amalgam fillings had three times more mercury in the brain and nine times more in the kidneys than did people with no amalgam fillings.

Read more:
Amy, do you have pointers to studies of the effects of ethyl mercury on the brain?
Amy, you really crack me up with this... Vaccinations have been around for over 200 years... "

You yourself dismiss the validity of WHOLISTIC healing methods of ALL kinds and say that just because they've been around for so long doesn't mean they work. And, then, you tout vaccines as the cure-all and say they've been around for 200 years.

By the way, different wholistic/natural healing systems have been around for THOUSANDS of years... which kicks major ass to allopathic medicine.

How ironic, eh?!

I'll keep eating my organic fruits and veggies and non-chemical, non-GMO, non-pesticide laced, vegetarian/vegan lowly processed or non-processed, whole grain foods and working out and using my wholistic/natural therapies, and you can continue taking your meds and getting your vaccinations.

I'd put my health up against just about anyone's.