Your joints are aching, you're gaining weight and your voice suddenly sounds oddly hoarse. You might think that these are the inevitable signs of aging beginning to creep into your life, but before you write them off, consider whether they could be symptoms of hypothyroidism.

The thyroid gland, located in the front of the neck just below the voice box, plays a crucial role in regulating hormones and metabolism, and when it's out of whack, the entire body can be affected. Hypothyroidism is a condition in which the thyroid gland becomes under-active, failing to properly secrete the hormones that help convert food and oxygen into energy. It can be caused by autoimmune diseases, birth defects, radiation treatment or the use of certain drugs like lithium.

If you are experiencing any combination of the 12 symptoms of hypothyroidism listed below, see your doctor for a physical exam and laboratory tests.

Sensitivity to cold - A sluggish metabolic rate will slow down your body's ability to produce heat. Cold hands and feet are a common symptom of slow thyroid function.

Fatigue - The impact of impaired thyroid function on metabolism also interferes with energy levels, making you feel unusually tired and sluggish.

Weakness - Sometimes, hypothyroidism causes a feeling of overall weakness as well as trembling in the muscles and slow breathing.

Depression - Hypothyroidism and depression may seem like two different conditions, but they're often linked. People suffering from depression should be tested for thyroid disorders, as thyroid-replacement medications may be a more effective treatment than antidepressants.

Pale, dry skin - Thyroid disease can significantly alter the look and feel of the skin. When the metabolism slows down, it may decrease sweating, causing dry skin that can lead to dermatitis, including eczema.

Menstrual irregularities or infertility - Low levels of thyroid hormone can decrease libido and cause menstrual abnormalities like increased bleeding. Both of these problems can lead to difficulty getting pregnant or outright infertility.

Joint and/or muscle pain - Aches, tenderness and stiffness in the muscles and joints are a key sign of hypothyroid disease. People with the most common form of hypothyroidism are at increased risk of developing other autoimmune diseases, like rheumatoid arthritis, as well as carpal tunnel syndrome and tendonitis.

Dry, thinning hair and brittle fingernails - It's not unusual for hypothyroidism to decrease oil production in the skin to the extent that hair loss occurs and fingernails become brittle, breaking easily. People with dysfunctional thyroids may find that they suddenly have dramatically thinning hair or even bald spots.

Unexplained weight gain - Slow metabolism and lack of energy make it easy to gain weight and difficult to lose the stubborn pounds that start to accumulate.

Puffiness in the face - A bloated-looking face with swollen, puffy eyelids and especially a thickening of the neck is a symptom of advanced hypothyroidism. You can do a Thyroid Neck Check on yourself using the instructions provided by the American Association of Clinical Endocrinologists (PDF).

Hoarse voice - Because the butterfly-shaped thyroid gland is so close to the larynx, it can have an effect on the sound of your voice if it becomes inflamed.

Elevated blood cholesterol - People with hypothyroidism often have high cholesterol as well. The slowed metabolic rate associated with this disease makes it difficult for the body to properly process fats in the blood.

Have other tips for people trying to understand the symptoms of hypothyroidism? Leave us a note in the comments below.

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