Major depression is one of the most common mental disorders in the United States. In 2015, an estimated 16.1 million American adults (age 18 or older) had at least one major depressive episode in the past year.

While people are starting to recognize and seek treatment for depression during the teen years and adulthood, depression in older adults often goes overlooked and untreated. Older adults face loss of partners, chronic physical illnesses, financial concerns and cognitive impairment.

Two recent studies took a closer look at the types of mental illness in elderly adults, as well as the causes.

Late-onset depression is common among older adults. More than 2 million people in the U.S. facing depression each year are over the age of 65. That means that 6 percent of the 34 million Americans age 65 and older suffer from some form of depression.

Depression is different for older adults. About 80 percent of older adults have at least one chronic health condition, and 50 percent have two or more. Depression is more common in people who also have other illnesses, such as heart disease or cancer, or whose function becomes limited.

About 58 percent of people aged 65 and older believe that it is normal to get depressed as they grow older. Most older adults suffering from depression tend to "handle it themselves." Only 42 percent would seek help from a health professional.

A recent study suggests that most people will develop a diagnosable mental disorder with only a minority of people experiencing enduring mental health. In this cohort, only 17 percent of repeatedly assessed participants managed to reach midlife (age 38) without experiencing the psychiatric symptoms and resulting functional impairment necessary to meet criteria for the diagnosis of a mental disorder.

However, another study suggests that well-being in later life may depend largely on psychosocial factors, such as stress, with physical impairments playing only a secondary role.

A team of researchers in Germany relied on data derived from about 3,600 participants with an average age of 73 who had taken part in the population-based KORA-Age Study. They used a questionnaire from the World Health Organization (the WHO-5 Well-Being Index) with a score range of 0 to 100 to investigate risk factors associated with low subjective well-being (SWB) in men and women separately, with a special focus on emotional distress.

Low SWB was significantly higher in women than in men (23.8 percent versus 18.2 percent). Low income, physical inactivity, multimorbidity, depression, anxiety and sleeping problems were associated with low SWB in both sexes. Living alone increased the odds of having low SWB in women, but not in men.

Depression and anxiety were the strongest risk factors of low SWB among men. In both sexes, anxiety had the highest population-attributable risk (men: 27 percent, women: 41 percent). Low income and sleep disorders also had a negative effect, but poor physical health had little impact on life satisfaction.

The study's important conclusions were that the mind plays an important role in well-being in later life and that women who live alone have a lower sense of well-being, suggesting the need for more appropriate services and interventions.