Medical disorders can make people prone to depression. For example, people who have dementia-causing brain disorders, such as Alzheimer's disease or Huntington's disease, are more susceptible to depression. In addition, stroke is known to trigger depression, affecting about 25 percent of those who have had a stroke in the left frontal area of the brain.
Hormonal disorders, such as an underactive thyroid (hypothyroidism) and Cushing's disease (in which the adrenal gland produces too much of the stress hormone cortisol, affecting blood pressure and metabolism) also can lead to depression. A recent study also suggests that low testosterone levels may be responsible for the increase in depression in men after age 65.
Vitamin deficiencies, such as insufficient levels of folic acid, vitamin B6, or vitamin B12, also have been linked to depression. (In one study of 700 women, those with a vitamin B12 deficiency were twice as likely to be severely depressed as those without this deficiency.)
Two recent studies also suggest that obese adults may be more likely to develop a mental health disorder, and those with the metabolic syndrome (a combination of excess weight, high cholesterol, high blood glucose levels, and high blood pressure) are at increased risk for depression.
Medications & Mood Disorders
Prescription drugs also can cause mood disorders. Medications such as corticosteroids, levodopa (Parcopa and other drugs used to treat Parkinson's disease), and methylphenidate (Ritalin and others, commonly used for treating attention deficit disorder) can trigger mania in bipolar disorder. Other drugs, including some used to treat high blood pressure and cancer, have been known to cause depression.