Thyroid and Bone Density: How an Overactive Thyroid Affects Bones

Does an overactive thyroid affect your bones?

Yes — an overactive thyroid (hyperthyroidism) speeds up bone loss and can lower your bone density, raising the risk of osteoporosis and fractures. This is a recognised link, not a fringe worry: the NHS lists osteoporosis — a condition that makes bones fragile and more likely to break — as a complication of an overactive thyroid (NHS).

The Royal Osteoporosis Society explains the underlying reason plainly: a high level of thyroid hormone increases the rate of bone loss, which raises the chance of developing osteoporosis and broken bones (Royal Osteoporosis Society). Importantly, this excess hormone can come from two directions — an untreated overactive thyroid, or taking too much thyroxine (levothyroxine) for an underactive thyroid (Royal Osteoporosis Society). We come back to that second, treatment-related route below.

How does an overactive thyroid weaken bones?

Thyroid hormone sets the pace of bone remodelling, and too much of it makes your skeleton break down bone faster than it can rebuild. Bone is constantly renewed in cycles of resorption (removal) followed by formation (replacement). In hyperthyroidism this cycle is thrown out of balance: a 2020 review in the Journal of Clinical Medicine describes overt hyperthyroidism as having a detrimental effect on bone through high bone turnover, a shortened remodelling time and a net loss of bone (Journal of Clinical Medicine, 2020).

The scale of that acceleration has been quantified. A 2013 review in the International Journal of Endocrinology reports that in hyperthyroidism bone turnover is accelerated roughly two-fold, the remodelling cycle runs in about half the normal time, and each cycle loses in the order of 9.6% of mineralised bone (International Journal of Endocrinology, 2013). Because each faster cycle removes more bone than it replaces, the losses stack up over time. A 2023 narrative review reaches the same mechanistic conclusion — a shorter remodelling cycle with more resorption than formation (Cureus, 2023). If you want the wider picture of how bone is lost, our guide to what causes osteoporosis sets out the common drivers.

Does an overactive thyroid raise your fracture risk?

It does — and the effect is strongest in postmenopausal women. The Journal of Clinical Medicine review reports that a prior history of hyperthyroidism is an independent risk factor for hip and vertebral fracture, with a relative risk of about 1.8, especially in postmenopausal women (Journal of Clinical Medicine, 2020). In other words, having had an overactive thyroid can leave a lasting mark on fracture risk even after the thyroid problem itself is dealt with.

For more severe or untreated overactivity, the numbers reported are higher still, though they rest on narrower evidence. The 2013 International Journal of Endocrinology review cites a prospective study in which a TSH below 0.1 mU/L was associated with a 4.5-fold risk of vertebral fracture and a 3.6-fold risk of hip fracture (International Journal of Endocrinology, 2013). Those are striking figures, but they come from a single prospective study reported within a review, so they are best read as illustrative of direction and magnitude rather than a settled multiplier. To understand how clinicians pull factors like this together into an overall estimate, see our explainer on fracture risk and FRAX.

What about subclinical hyperthyroidism — a low TSH with "normal" hormones?

Even a mildly overactive thyroid, where TSH is low but thyroid hormones still test normal (subclinical hyperthyroidism), is linked to more fractures. A large 2015 meta-analysis in JAMA, pooling 70,298 participants, found that subclinical hyperthyroidism — compared with normal thyroid function — was associated with an increased risk of hip fracture (hazard ratio 1.36, 95% CI 1.13–1.64) and of any fracture (hazard ratio 1.28, 95% CI 1.06–1.53) (JAMA, 2015).

The risk tracked with severity: the same analysis found it was higher when TSH was below 0.10 mIU/L, where the hip fracture hazard ratio rose to 1.61 (JAMA, 2015). This is the key reason a suppressed TSH is taken seriously for bone health, whether it comes from the thyroid itself or from thyroid medication.

Can taking too much levothyroxine weaken your bones?

The dose is what matters. Levothyroxine kept within the normal range is not linked to more fractures — the risk comes from over-replacement that suppresses your TSH. Reassuringly, a 2021 review of levothyroxine and bone concluded that levothyroxine used to maintain normal (euthyroid) hormone levels does not appear to carry a substantial risk of osteoporosis or fractures, and that people with a TSH of 0.4–4.0 mIU/L were not at increased fracture risk (Springer (NCBI Bookshelf), 2021).

The concern is with excess thyroid hormone. The 2024 UK NOGG osteoporosis guideline names thyroid hormone excess among the medications known to increase hip fracture risk, listing excess thyroid hormone treatment (levothyroxine and/or liothyronine) as a fracture-risk factor and flagging patients with thyroid cancer on TSH-suppressive therapy as at particular risk (Archives of Osteoporosis, 2025). Sometimes a suppressed TSH is deliberate and necessary — for example after thyroid cancer — and that is a clinical judgement your team balances against bone health.

Who is most vulnerable depends heavily on menopausal status. The Journal of Clinical Medicine review notes that postmenopausal women on TSH-suppressive levothyroxine are at risk of bone loss, whereas premenopausal women are not, and a meta-analysis found more significant bone loss in postmenopausal than premenopausal women on suppressive therapy (Journal of Clinical Medicine, 2020; Springer (NCBI Bookshelf), 2021).

Does an underactive thyroid (hypothyroidism) affect bone density?

On its own, an underactive thyroid is a much weaker and more indirect factor than an overactive one. The Journal of Clinical Medicine review is explicit that there are no clear data demonstrating a relationship between bone mineral density in adults and hypothyroidism (Journal of Clinical Medicine, 2020). And the 2015 JAMA meta-analysis found no association between subclinical hypothyroidism and fracture risk (JAMA, 2015).

The practical takeaway is that, for someone treated for an underactive thyroid, the bone concern is not the underactivity itself but the over-treatment scenario above — a dose high enough to push TSH down into the suppressed range.

If my thyroid is treated, will my bones recover?

Largely, yes — treating the overactivity usually slows bone loss back toward normal, though recovery is not guaranteed for everyone. The Royal Osteoporosis Society states that once hyperthyroidism is diagnosed and treated, the rate of bone loss should return to normal and bone strength should improve (Royal Osteoporosis Society). Longer-term data support real recovery of density: the International Journal of Endocrinology review notes that bone mineral density has been observed to return toward normal after 3–6 years of a restored normal (euthyroid) state following successful antithyroid therapy (International Journal of Endocrinology, 2013). Correcting thyroid function is often the central move — the 2023 narrative review notes that correcting thyroid function alone can often be enough to prevent excessive bone resorption (Cureus, 2023).

The important caveat is that this is not universal. The Royal Osteoporosis Society is careful to add that some people — especially postmenopausal women and those who had prolonged untreated disease — continue to lose bone (Royal Osteoporosis Society). That is exactly why knowing your baseline and tracking change over time is worthwhile, rather than assuming the problem resolves itself.

Should you have your bone health checked if you have a thyroid condition?

It is worth discussing with your doctor, particularly if you have extra risk factors. The Royal Osteoporosis Society advises anyone who has had hyperthyroidism and is worried about osteoporosis to talk to their doctor about a fracture risk assessment (Royal Osteoporosis Society). Based on the evidence above, a conversation is especially sensible if you:

• had prolonged or untreated overactivity before diagnosis;
• take a TSH-suppressive dose of thyroid hormone (for example, after thyroid cancer);
• are postmenopausal and have other risk factors such as a family history or previous fracture.

A bone-density scan turns guesswork into a number you can act on. In the UK, that assessment is usually a DXA scan, sometimes arranged through your GP — our guide to bone density scans on the NHS explains the usual route and its limits. Because bone loss linked to the thyroid plays out over years, the real value is in establishing a baseline and then monitoring how it changes.

This is where a radiation-free REMS scan fits alongside your medical care rather than replacing it. Because it uses no ionising radiation, it can be repeated to track bone health over time — useful when you and your clinician want to watch how things settle after treatment, or keep an eye on bone while on a suppressive dose. You can read more about our bone health assessment and how it complements the care your GP or thyroid clinician provides.

The bottom line on thyroid and bone density

An overactive thyroid — from untreated disease or from too much thyroid hormone — speeds up bone turnover and can lower bone density, raising fracture risk most clearly in postmenopausal women. Even a subclinically low TSH is associated with more fractures, and the 2024 UK guideline treats excess thyroid hormone as a fracture-risk factor. The encouraging side is that a correctly dosed level within the normal range is not linked to that harm, and treating an overactive thyroid usually lets bone recover toward normal — though not for everyone. An underactive thyroid, by contrast, is a weak and indirect factor. If you have a thyroid condition and any of the risk markers here, the smart step is to move from guessing to knowing: talk to your GP about a fracture risk assessment, and never change your thyroid dose on your own.

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This article is part of our bone health series. To understand how clinicians estimate your risk, read our guide to fracture risk and FRAX.