9 Signs of Low Thyroid Function

9 Signs of Low Thyroid Function

The thyroid is a part of the body we’ve all heard of, yet few of us really understand what it is or what it does for us.

If you know someone who has a thyroid problem, then you may know that they gained weight quickly and may have also had numerous other subtle symptoms that can be easily misdiagnosed.

But what does a healthy thyroid do in the body? Can it be “low” without being an under-active thyroid (known as hypothyroidism)? Read on to learn more.


What is your thyroid?

The easiest way to describe the thyroid is as the thermostat and fertilizer of the body. It’s what makes the decision to burn more or less fat to keep you at a good internal temperature. When your thyroid is thrown off balance, almost all functions in the body slow down. It is a gland in your throat that is in a butterfly shape and sits behind (and a little above) the area where your collarbones meet.


What are the signs of low thyroid function?

It’s important to note that symptoms of low thyroid can come on extremely slowly – over months and even years. That means you need to be vigilant and in-tune with how you feel when you’re healthy, as well as how your menstrual cycle affects your mood and energy levels. It’s not unusual to feel tired and moody around your time of the month, but if it’s happening at random times or even constantly, then it’s something to note. That said, here are some of the signs you should be looking out for:

1. Fatigue & Sluggishness

Fatigue and chronic fatigue is a big sign that your thyroid isn’t working optimally. Animals that hibernate have incredibly low thyroid levels as they lead up to a long period of sleep, so it’s no surprise to find that humans with low thyroid levels find it hard to make it through the day without taking a nap.

Another symptom is sluggishness, which differs slightly from fatigue because your reaction times, both physically and mentally are slow, and you may experience “brain fog” and feel unable to properly think things through.

2. Slow Gut Mobility

If you feel sluggish for a long time after a meal or experience constipation regularly, it can be due to low thyroid function. Low thyroid function slows the colon and makes it more difficult to pass waste on a healthy and normal schedule.

3. Brittle Hair and Nails

When your thyroid is low, your cells cannot replicate at a healthy rate, which can and will result in brittle hair and nails over time. One study even found that 25-30% of people seeing a hair loss specialist actually had abnormal thyroid function, and that figure increased to 40% for patients over 40 years old.

4. You Feel Cold All the Time  

As we explained earlier, the thyroid is the body’s internal thermostat, working to keep the body’s internal temperature at a constant. When the thyroid isn’t working properly, it may fail to send the right signals to let your body know that it’s cold and needs to do more to warm up. This means you’re more likely to feel cold even while others are a comfortable temperature. 

5. You Gain Weight Even While Dieting

Weight gain is a major symptom of an underactive thyroid because it is so intrinsically linked to your metabolism. If your metabolism is sluggish, it’s not going to help you burn the calories you’re eating and so you’re far more likely to gain weight, even if you’re not eating more than normal.

6. You Feel Down

Feeling low and symptoms of depression are also signs of low thyroid function. 64% of women and 57% of men with hyperthyroidism report experiencing depression and anxiety, so if you feel fatigue combined with anxiety or depression, it may be time to look at your thyroid health.

7. Muscle Aches and Cramps

In more extreme cases, you may experience muscle pain and cramps, as the body moves into “catabolism”, which is where the body cannibalizes muscle tissue for energy. This is necessary in a survival situation but can be triggered by low thyroid function. 34% of people with low thyroid report muscle aches and cramps despite not having increased physical activity.

8. Low Libido

It’s not uncommon to lose all interest in sex when your thyroid function is low. This can be partially the common fatigue and weight gain that those with low thyroid experience, but studies have linked low thyroid function to a low satisfaction or interest in sex, especially in women.

9. Irregular Periods

If your cycle seems disrupted, or if you start having unusually heavy periods, this can also be a sign of low thyroid function. A study found that 40% of women with low thyroid experienced irregular periods or heavy periods within the past year, compared to just 26% of those with normal thyroid levels.

Are all symptoms a sign of hypothyroidism?

You can experience abnormal thyroid function without it being hypothyroidism – in fact, 12% of people will experience some abnormal behavior at some point in their lives, and women are 8 times more likely to do so than men. Hypothyroidism often means that your thyroid cannot make the necessary hormones alone, so if you are worried you may be experiencing true underactive thyroid, schedule an appointment with your doctor to talk through your symptoms. 


Dr. Nancy Rahnama, MD, ABOM, ABIM, is a medical doctor board certified by both the American Board of Obesity Medicine and the American Board of Internal Medicine. Her specialty is Clinical Nutrition, that is, the use of nutrition by a medical doctor to diagnose and treat disease. Dr. Rahnama has helped thousands of people achieve their goals of weight loss, gut health, improved mood and sleep, and managing chronic disease. 

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