Slightly Underactive Thyroid May Be a Plus

Hyperthyroidism Slideshow

FRIDAY, June 12 (HealthDay News) -- Instead of being a medical problem in need of treatment, an underactive thyroid in old age might actually help you live longer, a new study says.

Researchers tested the levels of thyroid stimulating hormone (TSH) in 236 Ashkenazi Jews, who were about 100 years old, and their children, most of whom were in their 70s. For comparison with people not related by blood, they tested the TSH levels of the children's spouses.

The study found that the Ashkenazi centenarians had slightly elevated levels of TSH, which is a sign of mild hypothyroidism, or an underactive thyroid. The centenarian's children also had slightly elevated levels of TSH, compared with that of their spouses.

The thyroid, a butterfly-shaped gland in the front of the neck, helps regulate metabolism. Though researchers aren't sure why, a slightly slower metabolism might promote longevity.

"This is sort of a revolutionary finding," said study co-author Dr. Martin Surks, a professor of endocrinology and pathology at Albert Einstein College of Medicine and Montefiore Medical Center in New York City. "A year or two ago, higher TSH was thought to be a disease that might warrant treatment. These findings in this very select population suggest the opposite. Higher TSH could actually benefit you."

Surks and his colleagues also found that the centenarians and their offspring were more likely to have a particular variant of a TSH receptor. Those with that variant -- nearly 60% of the centenarians -- tended to have higher TSH levels.

"The implication is that if you have the variant, your TSH would be a bit higher, and that may be favorable to achieving extreme longevity," Surks said. "These are not huge differences in TSH levels, but over a lifetime they could be very, very important."

The study was to be presented this week at the Endocrine Society meeting in Washington, D.C.

Hypothyroidism, or not enough thyroid hormone, can cause feelings of weakness, depression and fatigue.

People with sluggish thyroids are also at greater risk of weight gain, high cholesterol and heart failure and a slight possibility of making borderline dementia worse, said Dr. Jacob Warman, chief of endocrinology at the Brooklyn Hospital Center in New York.

Though hypothyroidism can occur at any age, older people tend to get it more often. Women older than 60 are especially at risk.

In the recent past, doctors often treated underactive thyroid with medication, but that's changing, Warman said.

"I see a lot of people with this elevated TSH, and I usually do not treat all of them unless I see the TSH levels going up to above 10," he said.

A normal TSH level is generally considered to be between 0.5 and 4.5. In the study, 40% of centenarians had TSH levels over 2.5, Surks said.

However, Warman does recommend that people with elevated TSH levels take a blood test for Hashimoto's thyroiditis, a common cause of hypothyroidism in older adults. Hashimoto's is an autoimmune disease in which the body makes antibodies against the thyroid, slowly destroying it.

For people with Hashimoto's, using medication to treat the hypothyroidism is probably called for because the condition continues to worsen with time.

Dr. Stephen Rosen, chief of endocrinology at Pennsylvania Hospital and a clinical associate professor of medicine at the University of Pennsylvania, said he also does not treat slight hypothyroidism with drugs.

Too much thyroid hormone can also have ill effects, such as osteoporosis and irregular heartbeat, particularly a concern among the elderly.

"The decision to treat depends on what the TSH level is and the level of symptoms," said Rosen, an Endocrine Society spokesman.

He described the current study as fascinating. "We don't know why there is a population of people that can live to be 100," Rosen said. "This is beginning to get us some answers for what is important for that degree of longevity."

SOURCES: Martin Surks, M.D., professor, endocrinology and pathology, Albert Einstein College of Medicine and Montefiore Medical Center, New York City; Jacob Warman, M.D., chief, endocrinology, Brooklyn Hospital Center, New York City; Stephen Rosen, chief, endocrinology and metabolism, Pennsylvania Hospital, and clinical associate professor, medicine, University of Pennsylvania Health System, Philadelphia; June 12, 2009, presentation, Endocrine Society annual meeting, Washington, D.C.

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