Your thyroid may be a small body part, but it plays a big role in how you look and feel every day.

The butterfly-shaped gland is located in your lower neck and produces thyroid hormones T3 (triiodothyronine) and T4 (thyroxine), which affect everything from heart rate, metabolism and temperature regulation to energy level, skin changes, gut function and more. However, it’s the fatigue and weight issues caused by thyroid dysfunction that people really remember.

“Although the thyroid can affect weight, sometimes people like to make the thyroid the culprit of weight gain when it’s really caused by people not exercising or eating well,” explained Dr. Tracie Farmer of Novant Health Forsyth Endocrine Consultants. “It’s very common to say, ‘I’m tired and I’m gaining weight, it must be my thyroid.’ And it CAN be. But for the number of patients we see with complaints of weight gain and fatigue, only a small number can truly attribute their symptoms to thyroid dysfunction.”

That, of course, doesn’t mean that the thyroid isn’t worth investigating, but it does make it harder to know when to screen amid a population where obesity and fatigue run rife. “Fatigue especially can be affected by many, many things – the weather, mood, anemia, any chronic illness, medications – the list goes on and on,” Farmer said.

That said, an estimated 20 million Americans have some form of thyroid disease and up to 60 percent of those are unaware of their condition, according to the American Thyroid Association.

Over- and underactive thyroid issues and diagnosis

If the thyroid is overactive and produces too many hormones, also called hyperthyroidism, symptoms can include hot flashes, trembling, weight loss, hair loss, diarrhea, nervousness, fatigue, insomnia and a racing heart. The autoimmune disorder Graves’ disease is the most common cause of hyperthyroidism. Other causes include thyroid nodules, thyroiditis, consuming too much iodine and taking too much synthetic thyroid hormone.

By contrast, an underactive thyroid, also called hypothyroidism, can cause fatigue, slowed metabolism, joint and muscle pain, difficulty concentrating, constipation, cold sensitivity, dry skin, brittle hair and worsened depression. The autoimmune disorder Hashimoto’s disease is the most common cause , though other causes can include thyroid nodules, thyroiditis, congenital hypothyroidism, radiation of the thyroid, some medications and surgical removal of all or part of the thyroid.

“Fatigue can occur on either end of the spectrum – with too much or too little thyroid hormone,” Farmer said. “Similarly, people with hyperthyroidism can gain weight as opposed to losing because their metabolism is sped up and they’re eating more than they should. It just underscores the importance of screening if you believe there’s an issue.”

The gold standard for thyroid testing is a blood test that measures serum thyroid-stimulating hormone, or TSH, which is released by the pituitary gland and is what tells your brain to stimulate more or less thyroid hormone. A high TSH indicates your thyroid levels are too low. A low TSH indicates your thyroid levels are too high.

Normal TSH ranges also have been a source of debate as well. A normal TSH range was historically considered between 0.5 and 5 mIU/L. In 2002, those guidelines narrowed to a normal range of 0.3 to 3 mIU/L, according to the American Association of Clinical Endocrinologists.

“Lots of TV personalities have put a bug in people’s ears that TSH isn’t accurate or sufficient enough for testing, but I would say a vast majority of the time the TSH will catch most all thyroid dysfunction,” Farmer said. “Sometimes we’ll check T3 and T4 levels along with the TSH, but it’s a rare patient who only has T3 or T4 abnormality and a normal TSH. Thyroid ultrasound isn’t diagnostic for thyroid hormone dysfunction.”

Treatment

Treatment for hyperthyroidism aims to lower thyroid hormone levels through medication or radioactive iodine. Surgery to remove the thyroid is a last resort, Farmer said.

The most common treatment for hypothyroidism is levothyroxine (marketed as Synthroid or Levoxyl), which is synthetic T4 hormone. “Your body has 100 times more T4 than T3, and your body can easily convert the T4 into T3 as it needs it,” Farmer explained, adding that she takes into account three things when treating underactive thyroid.

“I make sure we put patients on enough hormone to bring their TSH into the low-normal range without overtreating. Overtreating can make patients swing the other way and have hyperthyroidism,” she said. “I also make sure patients switch to brand-name medication if they need to. Some patients just feel better on brand medication than generic.” And for the minority who still don’t feel well on Synthroid or Levoxyl alone, Farmer will add some prescription T3 to the mix.

“Once we achieve all that and a patient’s TSH level is within normal, whatever is left is probably not thyroid related,” Farmer said. “So once we get your TSH within normal range, if you are still gaining weight or feeling fatigued, the issue isn’t your thyroid.”

Farmer cautions against T3 and T4 combo preparations, typically used by alternative medicine practices, saying they “usually use ground-up pig thyroid. Pigs don’t have the same ratio of T3 and T4 that humans have, and within a pill the amounts can vary and there can be ups and downs in your TSH as a result.”

She also advised against using “thyroid care” supplements with high iodine content. “Excess iodine can do opposite things in different people,” Farmer said. “If patients want to make sure they get enough iodine, a regular balanced diet and a general multivitamin that includes both vitamins and minerals is enough.”

Feeling better

Carrie Lock, 35, of Charlotte, North Carolina, was diagnosed with hypothyroidism in February 2015. “I remember telling my doctor at one point, ‘I’m really tired,’ and she said, ‘You have a newborn.’ This was nearly three years ago,” Lock said. “It’s hard to know when my symptoms started, but I was aware my thyroid could be a problem because all of the women in my family have hypothyroidism.”

A physical in June 2014 was normal, but she asked her ob-gyn to recheck her TSH levels in February. Her TSH was 10 mIU/L, well over the recommended 3 mIU/L limit. “I’ve been taking Levoxyl for nearly a month and already feel better,” Lock said. “I’m able to get so much more done.”

She added, “Don’t let your doctor brush the issue aside, especially if you feel something is wrong.”

Lock’s story is common for people with thyroid issues, Farmer said, and underscores why correct diagnosis and treatment are so important. “Folks with thyroid issues generally feel better once they’re treated,” she said. “Untreated hypothyroidism also can put a strain on your heart, elevate your cholesterol, and cause cardiomyopathy and heart enlargement over time. So it’s really important to get to the bottom of any suspected thyroid problems.”