If you have a mildly underactive thyroid, your risk of developing heart failure is twice as high as someone with a normal thyroid level.

Heart failure occurs when your heart can’t pump enough blood to your other organs. This can cause fatigue, shortness of breath, and ankle swelling.

It’s been known for a while that hyperthyroidism (an overactive thyroid) and hypothyroidism (an underactive thyroid) can cause heart problems.

But a new study from the University of California at San Francisco School of Medicine in San Francisco shows that people with subclinical hypothyroidism are at risk, too.

Subclinical means you have a mildly underactive thyroid that’s only detectable by a blood test.

To find out if you have it, your doctor would order blood tests for thyroid-stimulating hormone (TSH) and free thyroxine levels.

If your TSH level is more than 4.5 mU/L and you have normal free thyroxine levels, then you have subclinical hypothyroidism.

If at some point, your free thyroxine levels fall below normal, then you’ll be diagnosed with overt hypothyroidism. This always requires thyroid hormone therapy.

In addition to heart failure, a mildly underactive thyroid may also speed up the development of osteoporosis, especially in postmenopausal women who are prone to it.

The UC study followed more than 3,000 adults 65 years and older over a 12-year period.

The results showed that individuals who had a TSH level greater or equal to 10 mU/L were twice as likely to develop heart failure as those with normal thyroid levels.

You should discuss this with your doctor, especially if thyroid problems run in your family. It may make sense to get your thyroid function checked periodically.