How much iodine is too much?

NEW YORK (Reuters Health) - Iodine deficiency is a major health problem worldwide, but a new study points to the potential downsides of too much iodine.

Iodine is a mineral found in iodized salt, seafood, eggs, dairy and some breads. It is used by the thyroid gland to help regulate metabolism and development, especially in babies and children.

Iodine deficiency during fetal and early-childhood development is a leading cause of brain impairments in much of the world. So most research has been directed at the effects of inadequate iodine.

Less is known about how much iodine is too much. So for the new study, reported in the American Journal of Clinical Nutrition, Chinese researchers randomly assigned healthy adults to take various doses of iodine supplements for four weeks.

They found that at relatively higher doses -- 400 micrograms a day and up -- study participants began developing what's called subclinical hypothyroidism.

That refers to a dip in the body's thyroid hormone levels, but with no obvious symptoms of hypothyroidism -- which include problems like fatigue, depression, dry skin and weight gain.

In this study, people taking 400-microgram supplements were getting around 800 micrograms of iodine per day when diet was factored in.

So the findings suggest that people -- at least in China -- should get no more than 800 micrograms a day, according to the researchers, led by Wanqi Zhang of Tianjin Medical University.

That's different from what's recommended in the U.S., where National Institutes of Health guidelines say the safe upper limit for adults is 1,100 micrograms of iodine per day.

Still, the typical American would get much less than 800 micrograms of iodine a day through diet anyway, according to Dr. Elizabeth Pearce, an associate professor of medicine at Boston University who was not involved in the study.

That said, Pearce cautioned against taking iodine supplements with more than 150 micrograms in a daily dose. And most Americans could skip supplements altogether.

"Overall, we're iodine-sufficient," said Pearce, who studies iodine sufficiency and thyroid function.

But she said there are certain people who may need supplements, including pregnant women.

In the U.S., adults are advised to get 150 micrograms of iodine each day; pregnant women should get 220 micrograms, while breastfeeding moms are told to get 290 micrograms.

The American Thyroid Association recommends that pregnant and breastfeeding women take a vitamin with iodine because low iodine can increase the risk of miscarriage and thyroid problems in moms, in addition to mental disabilities in babies.

According to Pearce, vegans may also want to take a supplement. In a recent study, Pearce and her colleagues found that the average iodine level in a group of 63 vegans was lower than what's recommended -- though their thyroid hormone levels were in the normal range.

Vegans eschew all animal products, including dairy and eggs, so their iodine sources may be few.

WHO YOU ARE, WHERE YOU LIVE

The current findings are based on 256 healthy adults who had normal thyroid when they entered the study. Zhang's team, which did not respond to requests for comment, randomly assigned them to take one of 12 doses of supplemental iodine -- anywhere from 0 to 2,000 micrograms per day, for four weeks.

Of the people who took 400 micrograms, 5 percent developed subclinical hypothyroidism. And the numbers rose in tandem with the iodine dose: Of people on the highest dose (2,000 micrograms per day), 47 percent developed subclinical hypothyroidism.

"These are interesting data," Pearce said, "because we don't have a lot of information on iodine excess."

Subclinical hypothyroidism has no obvious symptoms, but studies have linked it to an increased risk of heart disease over the long term, Pearce noted.

Those studies don't prove that subclinical hypothyroidism is to blame. Still, they raise concerns that there could be health consequences.

But in general, Pearce said, it's thought that the effects of your iodine intake may depend on "who you are and where you live."

In certain parts of the world, the soil is low in iodine, and people who eat mainly local foods have a high risk of deficiency. In other parts of the world -- Japan, for example -- people have a high iodine intake starting early in life, and they seem to "tolerate" that high level, Pearce explained.

In China, natural iodine levels vary by region. The country introduced universal salt iodization in 1996, so the problem of iodine deficiency has been controlled in most areas.

But Pearce said it's not clear if the adults in this study had adequate iodine intake early in life. If not, that could be a factor in their response to iodine supplements.

SOURCE: http://bit.ly/zQWJF4 American Journal of Clinical Nutrition, online.

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Vitamin D doesn't ease lung disease symptoms: study

NEW YORK (Reuters Health) - In a new study of people with moderate or severe lung disease, taking large amounts of vitamin D was not linked to any symptom relief, researchers from Belgium report.

Prior research suggested that up to three quarters of people with severe chronic obstructive pulmonary disease, or COPD, are deficient in the vitamin. So it was thought that giving them extra vitamin D might help prevent exacerbations in symptoms or trips to the hospital because of shortness of breath or mucus in the airways -- but that turned out not to be the case.

"Supplementation with vitamin D is not going to cure their disease," said Dr. Wim Janssens, one of the study's authors from University Hospitals Leuven.

"It is again clear for COPD patients that these exacerbations are really hard to treat" and prevent, Janssens told Reuters Health.

"There are a lot of relapses. We're basically failing in treating these."

Though vitamin D is most often associated with bone health and osteoporosis, Janssens said the theory has been that the vitamin may help reduce inflammation, including inflammation in the airways that worsens COPD symptoms, such as coughing and trouble breathing.

COPD is irreversible impairment of lung function, including emphysema and chronic bronchitis, often caused by smoking. One large national health survey suggests some 24 million Americans have the condition, according to the Centers for Disease Control and Prevention.

Janssens and his colleagues randomly assigned 182 people at their hospital with moderate to severe forms of the disease to take high-dose vitamin D pills, or a vitamin-free placebo pill, every four weeks for a year. One hundred and fifty of them finished the study.

Over that year, patients on vitamin D reported a total of 229 exacerbations in symptoms, for an average of 2.8 exacerbations in each patient. That was not statistically different from the 239 exacerbations, or 2.9 per patient, among those taking the placebo.

Symptoms were severe enough to send patients taking vitamin D to the hospital 79 times during the study, and people in the placebo group 73 times.

There was also no difference between the two groups in the amount of time until patients had their first exacerbation, or in measures of lung functioning, fatigue or the risk of death.

The researchers did find that among 30 people who had a very severe vitamin D deficiency at the start of the study, those taking the supplements had fewer problems with symptoms.

But because they didn't plan to explore that question from the beginning, and only found it on a second look at the data, it's hard to tell what the finding means.

"That would indicate that if there's any effect, there might be something in patients with really low levels. That's not the majority of patients with COPD," said Dr. Ken Kunisaki, from the Minneapolis VA Healthcare System.

More research would be needed to confirm if the vitamin is of any benefit even in those very deficient patients, added Kunisaki, who has also studied vitamin D in COPD but wasn't involved in the new research.

He said the current findings are in line with other research suggesting that although vitamin D deficiency might be more common in people with COPD, higher levels don't necessarily seem to equate with fewer symptoms.

"Unfortunately the results have been somewhat disappointing," Kunisaki said. "Right now there's no evidence that patients with COPD are going to benefit from additional vitamin D."

Researchers have also proposed that vitamin D may be helpful in patients with multiple sclerosis or tuberculosis, among other diseases, but studies generally haven't panned out, Janssens and his colleagues wrote in their report, published Monday in the Annals of Internal Medicine.

He said that in spite of his team's lack of positive findings, people with or without COPD shouldn't ignore very low vitamin D levels.

"If you're deficient, you need supplementation to normal levels just to treat your bone, to protect from osteoporosis and fractures," he said. "If you (have) severe deficiency, supplementation might also be effective for inflammation" associated with COPD.

Kunisaki cautioned that researchers still don't know whether there are long-term risks associated with taking high doses of vitamin D or other vitamins.

SOURCE: http://bit.ly/atTzv0 Annals of Internal Medicine, online.

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