Hypothyroidism: Understanding an Underactive Thyroid

You're tired all the time, but you chalked it up to work. Your hair is thinning, but you figured it was stress. You're gaining weight despite eating the same way you always have. You're cold when nobody else is cold. Taken individually, each of these could mean a dozen things. Together, they often point to one: your thyroid isn't doing its job.

Hypothyroidism, or an underactive thyroid, affects roughly 5% of Americans age 12 and older, with millions more undiagnosed, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). It's especially common in women over 60, though it can show up at any age, in any body, and it frequently gets missed because the symptoms overlap with so many other conditions.

Key Facts

• Prevalence: About 5% of the U.S. population; up to 10-15% in women over 60
• Typical onset: Gradual, often over months or years; peak diagnosis between ages 40-60
• Commonly confused with: Depression, chronic fatigue syndrome, normal aging, iron deficiency anemia
• When to see a provider: If you have persistent fatigue, unexplained weight gain, cold intolerance, or dry skin that doesn't respond to basic treatment

Symptoms of Hypothyroidism

Hypothyroidism slows things down. Your metabolism, your energy, your digestion, your mental sharpness. The symptoms tend to creep in gradually, which is why many people live with them for years before getting tested.

Common symptoms include:

• Fatigue and sluggishness that persist despite adequate sleep
• Weight gain or difficulty losing weight
• Cold intolerance, especially in your hands and feet
• Dry skin and brittle nails
• Hair thinning or hair loss, particularly the outer third of the eyebrows
• Constipation
• Muscle weakness, aches, or stiffness
• Joint pain or swelling
• A puffy face, particularly around the eyes
• Hoarseness or a deeper voice
• Heavier or irregular menstrual periods
• Slowed heart rate
• Memory problems or difficulty concentrating (sometimes called "brain fog")
• Depression or low mood

The tricky part is that almost every one of these symptoms has multiple possible causes. Fatigue alone could be sleep apnea, anemia, depression, or just poor sleep habits. That's why a blood test is essential. You can't diagnose hypothyroidism by symptoms alone.

These symptoms may indicate hypothyroidism, but only a qualified provider can diagnose you. A simple blood test takes the guesswork out of it.

What Causes Hypothyroidism

Your thyroid is a small, butterfly-shaped gland at the base of your neck. It produces hormones (T3 and T4) that regulate metabolism, body temperature, heart rate, and energy. When it produces too little of these hormones, everything slows down.

The most common cause in the United States is Hashimoto's thyroiditis, an autoimmune condition in which your immune system attacks the thyroid gland. Over time, this damage reduces hormone production. Hashimoto's accounts for about 90% of hypothyroidism cases in the U.S.

Other causes include:

• Thyroid surgery. Removing part or all of the thyroid for nodules, cancer, or Graves' disease eliminates the source of hormone production.
• Radiation therapy. Treatment for head and neck cancers or radioactive iodine treatment for hyperthyroidism can damage the thyroid.
• Certain medications. Lithium, amiodarone, interferon alpha, and some immunotherapy drugs can suppress thyroid function.
• Iodine deficiency. Rare in the U.S. due to iodized salt but still a leading cause worldwide.
• Pituitary gland disorders. The pituitary controls thyroid hormone production. A tumor, surgery, or radiation affecting the pituitary can lead to secondary hypothyroidism.
• Postpartum thyroiditis. Temporary thyroid inflammation after pregnancy that affects about 5-10% of women; it sometimes becomes permanent.
• Congenital hypothyroidism. About 1 in 2,000-4,000 newborns is born with an underactive or absent thyroid, which is caught by newborn screening.

Women are 5-8 times more likely to develop hypothyroidism than men. Having one autoimmune condition (type 1 diabetes, celiac disease, rheumatoid arthritis) increases the risk of developing another, including Hashimoto's.

How Hypothyroidism Is Diagnosed

Diagnosis starts with a blood test measuring thyroid-stimulating hormone (TSH). TSH is produced by the pituitary gland and tells the thyroid to make hormones. When the thyroid is underperforming, TSH rises as the pituitary tries to compensate.

• Normal TSH: Typically 0.4-4.0 mIU/L (ranges vary slightly by lab)
• Elevated TSH: Suggests the thyroid isn't producing enough hormone
• Free T4 (thyroxine): Measured alongside TSH. Low free T4 with high TSH confirms primary hypothyroidism.

Subclinical hypothyroidism is when TSH is mildly elevated (usually 4.5-10 mIU/L) but free T4 is normal. You may or may not have symptoms. Treatment decisions here are individualized, not automatic.

Your provider may also test:

• Thyroid peroxidase antibodies (TPO): If positive, points to Hashimoto's as the underlying cause
• Free T3: Occasionally useful but not routinely needed for diagnosis
• Thyroid ultrasound: If nodules or structural abnormalities are suspected

The American Thyroid Association recommends screening adults at age 35 and every 5 years after, with more frequent testing for those with risk factors.

Treatment Options for Hypothyroidism

The standard treatment is straightforward: replace the hormone your thyroid isn't making.

Levothyroxine is the most commonly prescribed medication. It's a synthetic form of T4, the primary hormone your thyroid produces. It's taken once daily, on an empty stomach, 30-60 minutes before eating.

Key treatment details:

• Dosing is based on your weight, age, and how much thyroid function remains. Most adults start at 1.6 mcg per kilogram of body weight per day.
• Your provider will recheck TSH 6-8 weeks after starting or adjusting the dose. It takes that long for levels to stabilize.
• The goal is to bring TSH into the normal range (and keep it there) while resolving symptoms.
• Once stable, TSH is typically monitored every 6-12 months.
• Don't take levothyroxine with calcium, iron supplements, or antacids. They interfere with absorption. Separate by at least 4 hours.
• Coffee and high-fiber meals within an hour of your dose can also reduce absorption.

Combination T4/T3 therapy (adding liothyronine) is used in some cases where patients on levothyroxine alone continue to have symptoms despite normal TSH. This approach is controversial and not endorsed as first-line by most endocrinology guidelines, but it may be appropriate in specific clinical situations.

Desiccated thyroid extract (pig-derived thyroid hormone) is sometimes requested by patients. It contains both T4 and T3. The American Thyroid Association does not recommend it as first-line therapy due to inconsistent T3 dosing, but some providers use it when patients don't respond to levothyroxine alone.

Most people with hypothyroidism need lifelong treatment. The condition itself doesn't resolve on its own (except in some postpartum cases), but with proper medication, most symptoms improve within 2-4 weeks, with full effect by 6-12 weeks.

When to See a Provider

If you've been tired for months and can't explain it, that's worth a blood test. Add in weight gain, hair loss, cold sensitivity, or constipation, and the case for checking your thyroid gets stronger.

If you're already on thyroid medication and still feel off, your dose may need adjusting, or the absorption may be compromised. Don't assume the medication "isn't working" without rechecking your TSH.

If you're pregnant or planning to become pregnant, thyroid function is especially important. Uncontrolled hypothyroidism during pregnancy increases the risk of miscarriage, preeclampsia, preterm birth, and developmental problems in the baby. The American Thyroid Association recommends TSH be kept below 2.5 mIU/L in the first trimester.

How Ascend Treats Hypothyroidism

At Ascend Mind and Body, thyroid management falls under our primary care practice. Dr. Jason Saylor, DO evaluates and manages hypothyroidism at our Wesley Chapel and Tampa locations.

We start with a complete thyroid panel, not just TSH. If Hashimoto's is suspected, we'll check TPO antibodies. If your numbers are borderline, we'll discuss whether to treat or monitor, based on your symptoms, not just a lab threshold.

For patients already on medication, we review your dosing, timing, and anything that might be interfering with absorption. We recheck labs on a schedule that makes sense for where you are in treatment, more frequently when adjusting, less frequently when stable.

If your thyroid condition is contributing to other issues like elevated cholesterol or weight management challenges, we coordinate that care in the same practice.

Currently accepting Aetna in-network, with additional insurance carriers in the credentialing pipeline. Visit our new patients page for current details and scheduling.

This article is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare provider for diagnosis and treatment.

This article is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare provider for diagnosis and treatment.