Hypothyroidism — known as low thyroid — may cause depression. Hypothyroidism is a “condition in which the body does not get enough thyroid hormone for optimal brain and body functioning,” according to Gary S. Ross, M.D., in Depression & Your Thyroid: What You Need to Know.
Research has found a link between hypothyroidism and depression. For instance, there’s some evidence that people with depression tend to have higher rates of hypothyroidism than the general population (such as this study). A 2004 study found that 38 percent of older patients with hypothyroidism also reported symptoms of depression.
Unfortunately, hypothyroidism often goes undiagnosed. Some people simply aren’t tested for thyroid problems, while others are, but their lab tests come back “normal,” Dr. Ross notes.