Babies Excrete Vaccine-mercury Quicker Than Originally Thought, Study Shows

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Babies Excrete Vaccine-mercury Quicker Than Originally Thought, Study

Shows

http://www.sciencedaily.com/releases/2008/01/080130140135.htm

February's issue of Pediatrics offers another reason to rethink

blaming the spike in autism diagnoses on thimerosal, a mercury-

containing preservative routinely used in several childhood vaccines

until the late '90s.

New research from the University of Rochester suggests that infants'

bodies expel the thimerosal mercury much faster than originally

thought -- thereby leaving little chance for a progressive building

up of the toxic metal. This debunks the great myth, believed by both

parents and some pediatricians, that the gauntlet of thimerosal-

containing shots many infants received in the 1990s -- when the

average number of vaccines kids received increased sharply -- had put

them at risk for developmental disorders.

" Thimerosal has been used for decades, but the surge in vaccinations

caused fear that possible accumulations of ethyl mercury, the kind in

thimerosal, might exceed safe levels -- at least, when based on the

stringent risk guidelines applied to its better-understood chemical

cousin, methyl mercury, which is associated with eating fish, " said

Pichichero, M.D., professor of Microbiology/Immunology,

Pediatrics and Medicine at the University of Rochester and the

study's main author.

But scientists are learning that the two mercury species actually

behave quite differently.

Previous research conducted in Seattle just a few years ago

demonstrated that the ethyl mercury has a more difficult time

crossing the blood-brain barrier, posing even less toxic risk than

methyl mercury. This is especially telling, since even methyl mercury

itself has also proven rather benign at low levels. In fact, just a

few years ago, a Rochester study showed that children born to mothers-

to-be who ate an average of 12 meals of fish a week -- about 10 times

the amount that the average U.S. citizen eats -- showed no harmful

symptoms.

And now, the most recent research from Rochester unveils further

differences between the two types of mercury: the body rids the kind

found in thimerosal more that 10 times faster than it removes the

kind one might encounter in a Friday night fish fry.

In the Rochester study, 216 infants from R. Gutierrez Children's

Hospital (in Buenos Aires, Argentina, where thimerosal is still

routinely used in vaccines) were divided into three age groups to

have their blood-mercury levels tested both before and after shots

were administered at either their newborn, 2- or 6-month checkup.

Researchers learned that, in all three age groups, the half-life of

ethyl mercury in the blood -- or, the time it takes for the body to

dispose of half the mercury, and then another half, and so on -- was

measured to be 3.7 days. That's a far cry from the blood half-life of

methyl mercury, which is 44 days.

" Until recently, that longer half-life was assumed to be the rule for

both types of mercury. Now it's obvious that ethyl mercury's short

half-life prevents toxic build-up from occurring. It's just gone too

fast, " Pichichero said.

To illustrate, researchers cite that infants in the 6-month-old

group -- who, in their lifetimes, had encountered more total ethyl

mercury that any other group studied -- still had the same pre-

vaccination blood-mercury levels before their checkups as most 2-

month-olds had before theirs. This suggests that, before each round

of shots, the mercury has plenty of time to be cleared.

The study also showed that ethyl mercury was nearly undetectable in

urine samples; instead, it seemed that most of it was eliminated via

stools. That's good, because mercury in large amounts is toxic to

kidneys -- yet in the study sample, there was no evidence of any harm

to renal tissues.

These findings come in the wake of recent news from the California

Department of Health, which reported last month that autism rates

continue to mushroom in spite of the widespread removal of thimerosal

from most U.S. childhood vaccines in 2001, though it continues to be

used in vaccines used elsewhere in the world.

Thimerosal, hailed for its bacteria-killing properties, has been a

vaccine staple ingredient since the 1930s. But when the Environmental

Protection Agency announced in 1999 that the cumulative exposure

children typically received in vaccines might exceed a safe level for

intake based on methyl mercury statistics (even this " safe level " was

placed ten times lower than the amount held to pose real risk),

public health officials, together with the American Academy of

Pediatrics, recommended its removal -- though still without concrete

evidence of harm. The decision demanded a new formulation be created

and administered -- at a higher cost.

" Though it's reassuring to affirm that these immunizations have

always been safe, our findings really have greater implications for

world health, " Pichichero said. " Replacing the thimerosal in vaccines

globally would put these vaccines beyond what the world community

could afford for its children. It's a relief we haven't cause to do

that. "

Pichichero has served as consultant to the World Health Organization,

and his research has held considerable weight in the WHO decision to

continue using thimerosal in vaccines administered in nations outside

the United States.

In the past, Pichichero has also served as a consultant to vaccine

manufacturers including GSK Biologicals, sanofi pasteur, Wyeth

Pharmaceuticals and MedImmune.

This research was supported by the National Institute of Allergy and

Infectious Diseases of the National Institutes of Health. It was

performed in conjunction with investigators Gentile, M.D,

Norberto Giglio, M.D., and Umido, M.D., of R. Gutierrez

Children's Hospital in Buenos Aires; Gotelli, Ph.D., and

no Gotelli, Ph.D., of the Center of Toxicology Research in

Buenos Aires; Lihan Yan, M.S., of EMMES Corp in Rockville, land;

and son, Ph.D., Elsa Cernichiari, M.S., Grazyna Zareba,

Ph.D., and Treanor, M.D., of the University of Rochester.