Is lower thyroid activity linked to longevity?
NEW YORK |
NEW YORK (Reuters Health) - A less active thyroid may mean more years added to your life, hints a new Dutch study.
However, the researchers emphasize that the finding, which builds on prior evidence touting the possible link, still does not prove that decreased thyroid function is the fountain of youth -- it may just be related to something else that is.
"In an earlier study, we observed that middle-aged children of long-lived siblings have lower thyroid function compared to controls from the general population," Diana van Heemst of Leiden University Medical Center, in the Netherlands, told Reuters Health in an email.
"In the current study, we sought to assess whether in the generation of the long-lived siblings low thyroid function was related to enhanced survival of the parents of the siblings as well," she said.
The researchers studied 859 siblings from 421 long-lived families. As reported in the Journal of Clinical Endocrinology and Metabolism, their average age of 93 years old far exceeded current U.S. life expectancy of about 78 years.
After rating the longevity of these siblings' parents, the team analyzed the thyroid hormones in the siblings' blood. The two sets of values appeared to be strongly linked, supporting previous findings of heritability in decreased thyroid functioning and its relationship to long life, they say.
This result held up even after accounting for critical illness, which can also affect thyroid activity.
From its location in the neck, the thyroid secretes hormones that affect metabolism. The researchers suggest that the lower activity of thyroid hormones could shift the body's energy expenditure away from growth and proliferation in favor of protective maintenance, keeping the body healthier longer. However, other factors could be associated with both thyroid function and longevity, removing credit from the thyroid.
"These results may come as (a) surprise as low thyroid function is commonly regarded as a risk factor for cardiovascular disease," said van Heemst. "The prevailing recommendation therefore is to treat elderly with low thyroid function with hormone supplementation."
But it is still too early to say whether this practice cheats the elderly of some extra years.
"These data underpin the need for a dedicated clinical trial to test whether treating (mild decreases in thyroid function) with thyroid hormone supplementation is effective in the elderly," van Heemst said.
SOURCE: link.reuters.com/weq78n The Journal of Clinical Endocrinology and Metabolism, online August 25, 2010.
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Of course, the researchers are not saying that failing to treat an underactive thyroid — or undertreating hypothyroidism — will improve longevity in any way whatsoever. They don’t even know if there is any connection whatsoever between the thyroid function and the longevity.
Apparently, the theory is that lower activity of thyroid hormones may be redirecting the body’s limited energy supply toward health.
But there is no evidence to prove this, and the longevity may be due to other factors, and not the thyroid.
Unfortunately, every time a study like this comes out, some practitioners see this as vindication for failing to treat subclinically hypothyroid patients, and for failing to adequately treat hypothyroidism.
“Hey, be grateful you’re slightly hypothyroid,” they say. “You’ll probably live longer.”
Meanwhile, they ignore all the actual proven research that shows the demonstrated link between subclinical hypothyroidism and the risk of heart disease, depression, obesity, infertility, and a host of other health concerns.
Last year, we had a similar study of Ashkenazi Jews who lived to be 100. (You can read about it at http://thyroid.about.com/b/2009/06/12/underactive-thyroid.htm — titled “Slightly Underactive Thyroid May Make You Depressed, Overweight, at Risk of Heart Disease and Chronically Ill.”
Now we have the same situation again — a specific group of people who have a genetic connection to one another, and who have exceptional longevity. They also have somewhat higher TSH levels.
So a subset of researchers publish their findings. Which the “jump to conclusions” media, always looking for that “Fountain of Youth Discovered: News at 11″ headline, then proceed to declare, “Lower Thyroid Function Helps You Live Longer.”
Meanwhile, the real issue is what is really going on with these exceptionally long-lived folks and their thyroid glands? Are they evidence that yes, all the research on subclinical hypothyroidism is wrong? And actually, walking around your whole life subclinically hypothyroid — and perhaps, if we polled these people, suffering from a sub-par quality of life — is the key to longevity?
Or is the truth that some people with exceptional longevity have variants in their genetic makeup, and likely, their thyroid hormone receptors, allow them to have somewhat higher TSH levels, and yet not be physiologically hypothyroid or suffer hypothyroidism symptoms? Do they have a genetic variation that confers longevity on them, but has no ramifications whatsoever on the thyroid treatment of the general population who don’t share DNA with them?
Ultimately, though, as long as researchers and endocrinologists fail to understand that the TSH test is a measure of a pituitary hormone — and not a reflection of the body’s ability to properly absorb and utilize thyroid hormone — we’ll keep having studies like this.
Mary Shomon, Thyroid Patient Advocate
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