Could You Have a Sluggish Thyroid and Not Know It?


A woman checking her thyroid gland

Are you doing everything right – exercising, eating a clean diet, getting enough sleep – and still gaining weight? Somewhere in the back of your mind, you might wonder whether your thyroid gland is working against you, making it harder to shed those extra pounds. You’ve had your thyroid function checked and it was within normal range – but could It STILL be your thyroid?

The Mysteries of Your Thyroid Gland

Your thyroid, located at the base of your neck just below your Adam’s apple, is appropriately called the “master gland.” That’s because this butterfly-shaped structure in your neck regulates your metabolic rate, along with other functions such as temperature regulation. Unfortunately, things can go wrong with your thyroid gland – it can become overactive and underactive. An underactive thyroid gland is fairly common, especially among middle-aged women. In fact, about 10 to 15% of the population has a mildly underactive thyroid gland. What’s even more concerning is this problem may be greatly underdiagnosed.

The medical term for an underactive thyroid gland is hypothyroidism. The most frequent cause of hypothyroidism is an autoimmune condition called Hashimoto’s thyroiditis. This condition is more common in women during and after menopause. Less common is an overactive thyroid gland, also known as hyperthyroidism. Hypothyroidism and Hashimoto’s thyroiditis becomes more common with age. You’re also at higher risk if you have another autoimmune disorder.

Thyroid Function Tests

How do you know if your thyroid is functioning normally? Your thyroid gland produces two thyroid hormones called T3 and T4. They churn out these hormones under the direction of hormone produced by the pituitary gland in your brain called TSH or thyroid stimulating hormone. TSH tells your thyroid gland to make more T3 and T4. When you visit a health care professional to have your thyroid checked, after feeling your thyroid gland to see if it’s enlarged, they’ll likely check how much TSH your pituitary is producing. They’ll also check your T4 level as a marker of how well your thyroid is responding. Both of these are checked with a single blood test.

What do these tests show if your thyroid isn’t working properly? If your thyroid gland is underactive, your pituitary gland produces more TSH in a feverish attempt to get your thyroid gland to make more T4. You’d also expect T4 to be low since your thyroid gland is underperforming and not responding to TSH as well as it should. Remember how we said the thyroid produces T3 and T4? It turns out that T3 is the most active form of thyroid hormone and your thyroid gland doesn’t produce a lot of it. It makes much more T4. What happens normally is your body converts T4 to T3, the active form. Unfortunately, some people have a hard time making that conversion. So, you can have a normal T4 level and have a sluggish thyroid because your body is still deficient in T3, the most active form of thyroid hormone.

Another reason you might not have enough T3, the active form of thyroid hormone, is because your body converts T4 to reverse T3. This can happen if you’re under stress, have recently been ill or had surgery, or are eating a very low-calorie diet. The problem with reverse T3 is that it has no activity. If little T4 is being converted to reverse T3, you have a sluggish thyroid even if your thyroid tests look normal. Most doctors don’t check for reverse T3 when they test for an underactive or overactive thyroid.

Full Thyroid Testing

What should you do if you think you have a sluggish thyroid gland and your thyroid tests are normal? Make sure they did full thyroid testing. The best test for “hidden” thyroid problems is a full thyroid panel. Rather than just testing TSH and T4, this test measures:


Free T3

Reverse T3

Free T4

Thyroid Peroxidase Antibodies

Thyroglobulin Antibodies

The latter two are antibodies to see if you have Hashimoto’s thyroiditis, the most common cause of an underactive thyroid in women. You can ask your doctor to run a full thyroid panel if you think your thyroid is sluggish.

What might tip you off that your thyroid is lazy? Continuing to gain weight even though you’re exercising, watching what you eat, and not overeating. Other signs and symptoms you might have, include:



Hair loss

Dry skin

Brain fog


Feeling cold most of the time

Fatigue and lack of motivation

Muscle cramps

Carpal tunnel syndrome

Enlargement of the thyroid gland in the neck

Irregularities in menstrual periods

Be aware that you can have these signs and symptoms with other health problems as well.

 Thyroid Problems Are on the Rise

Why is an underactive thyroid so common? Two minerals are vitally important for thyroid function – iodine and selenium. The best source of iodine is iodized salt. With the recent emphasis on low-salt diets, some people don’t get enough iodine. Another excellent source of iodine is sea vegetables.

How about selenium? You need selenium to convert T4 to active T3. Good sources of selenium are seafood, seeds, cruciferous vegetables, mushrooms, and chicken. By far the best source is Brazil nuts. Selenium is important but don’t take a selenium supplement without your doctor’s permission. High doses of selenium can be toxic. On the other hand, some studies suggest that selenium may be beneficial for treating autoimmune thyroid disease.

Another possible reason thyroid problems, particularly Hashimoto’s thyroiditis, are increasing is due to the number of toxins we’re exposed to. Studies show pollutants in the environment, ones that we’re exposed to everyday, impact thyroid function. Some medications also affect thyroid activity. Your doctor can tell you whether you’re taking such a medication.

The Bottom Line

If you’re slowly gaining weight despite leading a healthy lifestyle, especially if you’re over the age of 50, ask your doctor to check a full thyroid panel that includes all six tests, rather than just a TSH and T4. Make sure you’re getting enough iodine and selenium in your diet without taking supplements. Yes, your thyroid gland truly is the master gland when it comes to your metabolism. Be aware of any symptoms that suggest it’s not working properly.



Clin Endocrinol. 2013;78(2):155-164.

Clin Endocrinol. 2013;78(1):1-8.

Clinical Endocrinology and Metabolism. December 2013Volume 27, Issue 6, Pages 745–762.

Thyroid. 2010 Jul; 20(7): 755–761.doi:  10.1089/thy.2010.1636.

Endocrine Web. “Hypothyroidism: Potential Symptoms and Causes of an Underactive Thyroid Gland”


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Thyroid Health: How to Keep Your Thyroid Gland Healthy

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