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This is the most common thyroid disorder, occurring when the gland doesn't produce enough hormones and, as a result, metabolism slows.

How to spot it: Symptoms range widely, from frequent constipation, low energy levels and shortness of breath to weight gain, depression and hair loss. Your doctor can check your levels of thyroid-stimulating hormone (TSH) using a simple blood test. (If TSH is high, thyroid levels are low.)

To lower your risk: Since some forms of hypothyroidism may be genetic, the best thing you can do is check your family's medical history in case you need to be on the lookout for red flags.

Common treatment: Levothyroxine, a synthetic version of the thyroid hormone T4, regulates metabolism and steadies hormonal imbalances.