ONE of the most commonly prescribed drugs in the UK, used to treat a hormone condition, may be linked to a bone snapping disease, a study has found.
An underactive thyroid or hypothyroidism is where your thyroid gland, a small, butterfly-shaped gland in the front of the neck, doesn’t produce enough hormones.
The hormones the thyroid gland produces regulate many of the body’s functions, from metabolism to heart rate.
Around one in 20 people in the UK are affected by the condition, which is most commonly treated with levothyroxin.
But now, new research has suggested taking the medicine could raise the risk of bone-thinning disease osteoporosis.
Scientists from the US assessed the drug on dozens of patients and found the risk was still raised among those with “normal” levels of the thyroid-stimulating hormone.
Professor Shadpour Demehri, an expert in radiology at John Hopkins University in Maryland and study co-author, said: “Our study suggests that even when following current guidelines, levothyroxine use appears to be associated with greater bone loss in older adults.”
Dr Elena Ghotbi, study lead author and postdoctoral research fellow at John Hopkins University, added: “Data indicates that a significant proportion of thyroid hormone prescriptions may be given to older adults without hypothyroidism.
“This raises concerns about subsequent excess of thyroid hormone even when treatment is targeted to reference range goals.”
Levothyroxine is sold under the brand name Eltroxin and is a synthetic version of a hormone called thyroxine.
It replaces thyroxine if your thyroid gland cannot produce it and prevents the symptoms of hypothyroidism.
About three million people take levothyroxine for hypothyroidism, making it the most commonly prescribed thyroid hormone in the UK.
As part of the study, researchers assessed 81 patients on levothyroxine and 364 non-users with an average age of 73 and thyroid-stimulating hormone level of 2.35.
Normal levels for adults are 0.4–4.0 mIU/L, but can vary by age.
After six years they found those on levothyroxine suffered a “greater loss of total body bone mass and bone density”.
But the researchers added patients taking the drug who had a “normal” thyroid-stimulating hormone level also suffered bone mass and density loss.
Dr Jennifer Mammen, study co-author and associate professor of endocrinology at Johns Hopkins, said adults taking levothyroxine should discuss their treatment with a medic and regularly monitor their thyroid function tests.
She said: “A risk-benefit assessment should be conducted, weighing the strength of the indications for treatment against the potential adverse effects of levothyroxine in this population.”
The research will be presented in full at the Radiological Society of North America‘s annual meeting next week in Chicago.
THYROID hormone affects the rate of bone replacement so plays a crucial role in maintaining healthy bones.
Too much thyroid hormone (i.e. thyroxine) in your body speeds the rate at which bone is lost. If this happens too fast the osteoblasts may not be able to replace the bone loss quickly enough.
If the thyroxine level in your body stays too high for a long period or the Thyroid-Stimulating Hormone (TSH) level in your body stays too low for a long period, then there is a higher risk of developing osteoporosis.
Overactive thyroid (hyperthyroidism)
If you have an overactive thyroid the first step is to treat the overactivity. Once the level of thyroid hormone in your body has been reduced to a normal level the rate of bone loss will no longer be so rapid and the bone strength may improve.
Some people will have or continue to have bone loss, with or without thyroid disease. Postmenopausal women are at particularly high risk of this.
If you have had a long period of untreated hyperthyroidism and have other risk factors for osteoporosis and bone fractures, a bone density scan two to three years after you start thyroid treatment will help assess your risk. If a bone density scan shows osteoporosis then this can be treated with osteoporosis medication.
Underactive thryoid (hypothyroidism)
An underactive thyroid is not a risk factor for osteoporosis, says the British Thyroid Foundation.
If you are prescribed levothyroxine you should have regular blood tests at least once a year, to ensure your thyroid hormone levels are not too high.
Continuous high thyroid hormone levels may lead to developing or worsening of low bone density and osteoporosis.
Source: British Thyroid Foundation
Both men and women can have an underactive thyroid, although it’s more common in women.
Children can also develop an underactive thyroid and some babies are born with it.
All babies born in the UK are screened for congenital hypothyroidism using a blood spot test when the baby is about five days old.
Levothyroxin is the main treatment and you’ll usually have a blood test once a year to monitor your hormone levels.
If an underactive thyroid is not treated, it can lead to complications, including heart disease, goitre, pregnancy problems and a life-threatening condition called myxoedema coma (although this is very rare).
