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I’m tired and gaining weight. Is it my thyroid, doc?

August 10, 2016

Problems with fatigue and weight management are extremely common and the much-maligned thyroid gland is often blamed.

When this butterfly-shaped gland is underactive, it can cause a variety of symptoms (e.g. feeling cold easily, loss of energy, constipation, menstrual changes and weight gain).

The thyroid gland produces hormones which regulate human metabolism (how the body uses and stores energy). When a person fails to make enough thyroid hormone, we refer to it as hypothyroidism (underactive thyroid). Thyroid function is further controlled by a gland in the brain, known as the pituitary. The pituitary secretes thyroid-stimulating hormone (TSH), which prompts the thyroid to produce and release thyroid hormone. When the thyroid underproduces hormones, the pituitary releases more TSH encouraging the thyroid to work harder.

Hypothyroidism is, therefore, easy to diagnose using a simple blood test.

We look at the levels of thyroid hormone (T4) and TSH.

If a patient’s TSH and T4 levels are normal, the thyroid is functioning well so her symptoms must be caused by something else.

Primary hypothyroidism will be seen when TSH levels are higher than 4.5 mIU/L (local laboratory values may differ) and associated with a low T4. These patients require thyroid supplementation.

Sometimes, we find that the TSH level is high but the T4 is normal. This state is called subclinical hypothyroidism and shows mild thyroid failure. Research is conflicted whether it is necessary to treat subclinical hypothyroidism at all.

If the TSH is greater than 10, treatment is necessary. If, however, the TSH is between 4.5 and 10, I discuss it with the patient and individualize the decision to treat. Under these circumstances, it can be helpful to check for thyroid antibodies (TPOab) because patients with a positive TPO blood test will be at a higher risk of developing overt hypothyroidism in the future.

When someone is started on thyroid medication, repeat blood testing is needed every 6 weeks until normal levels are achieved.

Patients on long-term thyroid supplementation will need to have their thyroid levels monitored. If the dose of thyroid medication is <125mcg, levels need to be rechecked, at minimum, in 2 year intervals. If the dose is >125mcg, repeat testing is recommended in 1 year.

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