Post Primer: How iodine tablets help protect against radiation exposure

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Since an 8.9-magnitude earthquake hit Japan on Friday, the Fukushima 1 plant – which houses two nuclear reactors – has experienced two explosions and a third reactor has lost its cooling system. According to authorities, some radioactive vapour has been intentionally released to reduce the pressure on the reactors. The Japanese government has determined that the radiation around the plant is at a tolerable level for humans, but a 20-kilometre radius around the plant has been declared an exclusion zone. More than two hundred thousand people have been evacuated.

Japanese authorities have told the U.N.’s atomic watchdog they are making preparations to distribute iodine to people living near nuclear power plants. Concerns about the nuclear situation in Japan have sparked runs on iodine tablets in places as far away as Finland. (Finnish pharmacy reps said that some of their stores in central Finland ran out of iodine completely on Saturday.)

After the jump, the National Post found out why iodine pills are distributed when there is a potential threat of nuclear radiation.

THE FIRST THING YOU NEED TO KNOW….

There’s radioactive iodine, and non-radioactive iodine. (You can probably guess which one humans should avoid.)

WHAT IS RADIOACTIVE IODINE?

The most common example of radioactive iodine – iodine-131 – is a major product of uranium fission. After a nuclear event, radioactive iodine can be released into the air and inhaled. It can also contaminate the local food or water supply and in turn be ingested. The thyroid gland quickly absorbs radioactive iodine, which can be damaging. It was a major contributor to health problems after the Chernobyl disaster.

WHAT IS NON-RADIOACTIVE IODINE?

Potassium Iodide (KI) is a salt of stable iodine in medicine form. It is available as a tablet or liquid. The body needs stable iodine to make thyroid hormones.

HOW DO IODINE TABLETS WORK?

The thyroid gland absorbs both stable and radioactive iodine and cannot determine the difference between the two. When you take the tablets, the thyroid becomes “full” and will be unable to absorb any more iodine — either stable or radioactive — for the next 24 hours.

WHAT ARE THE TABLETS’ LIMITATIONS?

Iodine tablets cannot stop radioactive iodine from entering the body. Iodine tablets can only protect the thyroid from radioactive iodine, and no other parts of the body. And, if the nuclear radiation does not contain radioactive iodine, then iodine tablets will have no effect.

How effectively iodine tablets prevent the absorption of radioactive iodine depends on:

• How much time elapses between exposure to radioactive iodine and the consumption of iodine tablets.
• How fast non-radioactive iodine is absorbed into the blood.
• How much radioactive iodine a person is exposed to.

WHAT ABOUT IODIZED SALT?

While iodized table salt does indeed contain enough iodine to maintain a healthy thyroid under normal conditions, it does not contain enough to block radioactive iodine from being absorbed. Table salt should not be used as a substitute for iodine tablets.

WHO IS MOST AT RISK?

• The thyroid glands of a fetus are most vulnerable (all forms of iodine cross the placenta).
• Infants and children under 18-years-old are highly sensitive to the potentially harmful effects of radioactive iodine.
• The iodine present in breast milk is not enough to protect a breast-fed infant from radioactive iodine passing readily into the milk. The Centre for Disease Control and Prevention recommends that women who suspect they have been exposed to radiation switch from breastfeeding to formula.
• People who already have thyroid problems are also at a higher risk of injury.
• Adults over 40 years of age have the lowest risk of developing thyroid cancer or injury after contamination and have a greater chance of experiencing an allergic reaction. They should not take iodine tablets unless a very large does of radioactive iodine is expected and they are told to do so.

WHEN SHOULD YOU TAKE IODINE PILLS?

Local public health or emergency management officials will alert the public if it is necessary to take iodine tablets or other protective actions. They may also advise the public not to eat certain foods or drink specific beverages until a safe, radiation-free supply can be guaranteed. People should not take iodine tablets unless advised to do so because the risks — see side effects, below — may outweigh the benefits.

HOW MUCH IODINE SHOULD YOU TAKE?

According to the FDA:

• Adults – including women who are breastfeeding – should take 130 milligrams of stable iodine.
• Children aged 3 to 18 should take 65 milligrams. Children who weigh more than 150 pounds should take the adult dose, regardless of age.
• Nursing and non-nursing infants between 1 month and 3 years of age should take 32 milligrams.
• Nursing and non-nursing newborns should take 16 milligrams.

HOW OFTEN SHOULD YOU TAKE IODINE TABLETS?

Most often a single dose of iodine – which protects the thyroid gland for 24 hours – is all that is needed. Officials may request that the public take a dose of stable iodine every 24 hours for a few days if radioactive iodine will remain in the environment for a prolonged period of time. Pregnant and breastfeeding women and newborns should avoid taking multiple doses.

RISKS AND SIDE EFFECTS

• When officials advise the public to take iodine pills following a nuclear event, the benefits outweigh the risks.
• Taking a higher dose than is recommended will not provide more protection and can cause severe illness or death.
• People with thyroid disease should take iodine pills only under a doctor’s supervision.
• General side effects include intestinal upset, rashes and inflammation of the salivary glands.

With files from Reuters and Agence France-Presse
Source: the Centre for Disease Control and Prevention in the U.S.

National Post
adonnelly@nationalpost.com