Slightly-overactive thyroid tied to heart problems
Too little thyroid activity is tied to a slower metabolism, which can come with weight gain and weight-associated cardiovascular problems.
“The heart relies on thyroid hormone to function normally,” Razvi told Reuters Health. “It’s like diabetes: if you have too much (blood) sugar you have a problem, and if you have too little sugar, you have a problem.”
In a separate study published in the same journal, a group of researchers led by Razvi found that treating subclinical hypothyroidism - thyroid glands that are slightly less active than normal - with thyroid hormone was linked to fewer long-term heart problems.
Those findings came from a database of general practitioners who saw close to 5,000 people with underactive thyroids starting in 2001. About half of patients were prescribed the thyroid drug levothyroxine.
Among people aged 40 to 70, just over four percent of levothyroxine-treated patients developed heart disease during the next eight years, compared with close to seven percent who weren’t treated for low thyroid function.
There was no difference in the risk of heart disease for patients older than 70 who did or didn’t take levothyroxine, however, Razvi and his colleagues found.
Levothyroxine Treatment of Subclinical Hypothyroidism, Fatal and Nonfatal Cardiovascular Events, and Mortality
Salman Razvi, MD, FRCP; Jolanta U. Weaver, PhD, FRCP; Timothy J. Butler, MRCGP; Simon H. S. Pearce, MD, FRCP
Arch Intern Med. Published online April 23, 2012. doi:10.1001/archinternmed.2012.1159
Background Subclinical hypothyroidism (SCH) has been associated with ischemic heart disease (IHD); however, it is unknown whether treatment of SCH with levothyroxine sodium will reduce the risk of IHD. The aim of this study was to investigate the association between levothyroxine treatment of SCH with IHD morbidity and mortality.
Adding to the list of potential health concerns with subclinical hypothyroidism, a third study recently published in Obstetrics & Gynecology found that women with slightly-underactive thyroids were more likely to develop diabetes during pregnancy than those with normal thyroid function.
WHO TO TEST?
Rodondi pointed out that the new research can’t prove slightly-off thyroid function leads to heart disease or other health problems.
To make that claim, he said, would require a “gold standard” controlled trial, in which people just outside the normal thyroid range are randomly assigned to be treated or not and followed for the incidence of new disease diagnoses.
Dr. H. Gilbert Welch, who studies disease detection and overdiagnosis at the Dartmouth Institute for Health Policy and Clinical Practice in Lebanon, New Hampshire, said he thinks it’s time for that type of trial. But he called for a study that starts even earlier, when symptom-free people are split into groups of those who do or don’t undergo screening for thyroid problems.
“I think that’s the real question: should doctors be looking for thyroid abnormalities in patients who feel fine?” Welch, who wasn’t involved in the new research, told Reuters Health.
Relationship of Subclinical Thyroid Disease to the Incidence of Gestational Diabetes
RESULTS: Of the 24,883 women included in the study, 23,771 (95.5%) were euthyroid, 584 (2.3%) had subclinical hyperthyroidism, and 528 (2%) had subclinical hypothyroidism. The likelihood of gestational diabetes increased with thyrotropin level (P=.002). For example, when a pregnant Hispanic woman of average age and weight was used, the predicted percent of gestational diabetes increased from 1.9% to 4.9% as thyrotropin increased from 0.001 to 10 milliunits/L (P=.001).
CONCLUSION: The risk of developing gestational diabetes increases with thyrotropin level. This supports a relationship between subclinical hypothyroidism and diabetes diagnosed during pregnancy.
If screening does prove to be helpful, Welch said, the questions become: what level of thyroid function counts as “abnormal”? And, what’s the best treatment strategy?
“If you’ve got full-blown hypo- or hyperthyroidism, that does require treatment,” Razvi said. “It’s this mild, subclinical form which is the controversial one.”
SOURCE: Archives of Internal Medicine, online April 23, 2012 and Obstetrics and Gynecology, May 2012