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Do High Doses of Thyroid Medication Affect Your Bones?

Patients who take medicine to treat an underactive thyroid need to be cautious that they don’t take too much. Most patients on thyroid medicine have Hashimoto’s thyroiditis and a smaller number take thyroid medicine because of thyroid cancer or Graves disease. Too much thyroid medicine increases the activity of the osteoclasts (the bones that break down bone) and put you at an increased risk for breaking a bone. To find the correct dose, your health care provider will get a thyroid-stimulating hormone (TSH) blood test and once you are on the correct dose, monitor your levels at least once a year.

Thyroid hormone requirements decline with age, so a dose that was good for a patient at age 20 or 30, may be too high when they are in their 60s, 70s, 80s or 90s. Younger patients should target a level of TSH in the lower half of the normal range (especially those diagnosed because of weight gain), while patients in their mid-50s should target a TSH level in the upper half of the normal range. For older patients, studies have shown that a lower TSH level was associated with an increased risk of heart disease.

Thyroid Stimulating Hormone (TSH)   Typical normal range
Normal Range .35 – 5.0
Target for younger patients .35 – 2.5
Target for older patients 2.5 – 5.0

What to know about taking thyroid medicine

  • Take thyroid medicine at the same time every day to avoid fluctuations in TSH
  • Take thyroid medicine at bedtime for best effect at regulating thyroid levels.
  • Do not take your thyroid medicine with iron or calcium supplements or food because it can affect the absorption of the medicine.

Steps your health care provider may take when you are taking thyroid medicines. 

  • Know your bone density which can help inform you about your risk of breaking a bone and may be useful to monitor any potential bone loss.
  • If you are at high risk for breaking a bone, your health care provider may suggest an osteoporosis medication to reduce the harmful effects on your skeleton.
  • Take as low a dose as possible, for as short a time as possible — but talk with your healthcare provider before you make any changes.
  • Make sure that you get 3-4 servings of a calcium-rich food every day. If you cannot eat dairy or calcium-fortified food, you may need a calcium supplement.
  • Be sure that you have an optimal vitamin D level (≥ 30 ng/mL or ≥74.9 nmol/L). People with breast cancer and prostate cancer may need higher blood levels of vitamin D.
  • Practice great posture and use good body mechanics to prevent spine fractures.
  • Strengthen your legs and do balance exercises to prevent falls and fractures.
  • Remove trip hazards from your home.

Common thyroid medicines that affect the skeleton

  • Levothyroxine LT4 (Levoxyl®, Synthroid®, Unithroid®)
  • Armour Thyroid

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