According to the Anxiety and Depression Association of America, depression (major depressive disorder) is a common and serious medical disorder that negatively affects how you feel, the way you think, and how you act. It is defined as having feelings of sadness and/or a loss of interest in activities that you once enjoyed, and five of the following symptoms:

• Loss of or increase in appetite
• Insomnia or hypersomnia (sleeping too much)
• Loss of energy or increased fatigue
• Increase in purposeless physical activity (such as fidgeting or hand wringing) or retardation of physical motions
• Feeling worthless or guilty
• Difficulty thinking, concentrating, and making decisions
• Thoughts of death or suicide with no plans of suicide

Symptoms must last for two weeks or longer and represent a significant change from normal behavior, such as missing work or school.

This form of depression includes a dark or sad mood that is present for most of the day on most days for two years. For children and adolescents, they experience irritability for at least one year.

Diagnosis is dependent on having two of the following symptoms:

• Poor or large appetite
• Insomnia or hypersomnia
• Low energy or fatigue
• Low self-esteem
• Poor focus
• Difficulty making decisions
• Feelings of hopelessness

During this time, symptom-free periods last no more than two months. Symptoms aren't as severe as major depression. Major depression may precede persistent depressive disorder, and major depressive episodes may also happen during persistent depressive disorder.

This form of depression is a more serious form of premenstrual syndrome (PMS). PMDD causes extreme mood shifts that can disrupt work or school and affect relationships. Symptoms include sadness, irritability, anger, and hopelessness. It begins a week or two before the period and lasts until two or three days after the period begins.

Some medical conditions can cause depression. Disorders involving the reproductive system are commonly associated with depressive symptoms. Some other conditions include HIV/AIDS, diabetes, hypothyroidism, Cushing's syndrome, stroke, and Parkinson's disease.

This disorder occurs when someone goes through some type of major life change, such as moving, getting married, having a baby, or changing jobs. Symptoms usually disappear within 6 months of the event, or when the stress is removed.

SAD usually occurs in winter and seems to be caused by shorter days and lack of sunlight, though occasionally it occurs in spring or early summer. Decreased serotonin levels are thought to play a role. The lack of sunlight may also cause an imbalance in the body's melatonin levels (the sleep hormone).

Symptoms include:

• Low energy
• Insomnia
• Feeling depressed most of the day, almost every day
• Loss or increase in weight
• Irritability
• Difficulty focusing
• Thoughts of death or suicide
• Feeling worthless or guilty

Fall and winter SAD, also known as winter depression, involves oversleeping, appetite changes, especially a craving for carbohydrates, weight gain, and low energy.

Treatment includes light therapy (phototherapy), medications, and psychotherapy.

PPD occurs after childbirth, and those who develop PPD are more likely to develop major depression later in life.
Symptoms include loss of appetite, irritability, insomnia, and difficulty bonding with the baby.

• Depression is the leading cause of disability for ages 15 to 44.
• Over 41,000 people commit suicide per year with depression as the main reason.
• 264 million people suffer from depression worldwide.
• Women are more likely to suffer from depression than men and usually have different symptoms. Women often feel sadness, worthlessness, and guilt, whereas men tend to display tiredness, irritability, and anger.
• When young children are depressed they often refuse to go to school, don't want to separate from their parents, and worry about their parents dying. Teens tend to be irritable, sulky, get into trouble, and often develop food issues or a substance abuse habit. Older people tend to hide their feelings of depression as they don't want to admit sadness or grief.
• In 2017, 4.5% of U.S. adults had at least one major depressive episode with impairment; estimated to be around 11 million people.
• Of those major depressive episodes, 64% included severe impairment, 36% did not.

• As of 2017, 7.1% of the U.S. population age 18 and older were depressed (17.3 million adults).
• Adult women suffer higher rates of depression than adult males: 8.7% vs. 5.3%.
• Rates of depression were highest in the 18–25-year-olds (13.1%).
• Rates were highest among adults who reported two or more races (11.3%).
• The median onset is 32.5 years old.
• Nearly half of those diagnosed with anxiety also suffer from depression.
• Married people have a lower rate of depression than those who are single. However, unhappily married people have the highest rates of depression, and happily married men have the lowest rates.

• 25% of all cancer patients experience depression.
• Around 20% of people who have a heart attack experience depression soon after the heart attack.
• In 2017, 39% of all HIV/AIDS patients have experienced depression.
• It's estimated that 50% of all patients with Parkinson's will experience depression.
• 32% to 39% of people with anorexia nervosa experience depression.
• 35% to 50% of people with bulimia nervosa experience depression.
• 33% of binge eaters have been diagnosed with major depressive disorder.
• Around 20% of Americans who suffer from a mood disorder, such as depression, or anxiety, have a substance abuse problem. The symptoms of one disorder can make the other worse.
• Sufferers of diabetes are 2 to 3 times more likely to experience depression. Only 25% to 50% of people with diabetes and depression get diagnosed.
• 27% to 50% of women with polycystic syndrome (PCOS) report depression, compared to 19% of women without PCOS.
• The prevalence of obesity increased from 25.4% among those with no symptoms of depression to 57.8% among those with severe depression. Depression is associated with significant reductions in the frequency of exercise: 4.6 vs. 5.4 times per week for moderate exercise and 2.8 vs. 3.7 times per week for vigorous exercise. Depression is also associated with a significantly higher daily caloric intake among those with a body mass index (BMI) over 30—1831 vs 1543 calories.
• Almost 50% of people diagnosed with anxiety also suffer from depression.

• According to a study from Boston University involving 1,441 participants from March 31 to April 13th, 2020, rates of depression in all demographic groups have tripled, especially for those under financial stress.
• Rates increased from 8.5% to 27.8%, and the severity of depression increased as well. Mild symptoms went from 16.2% to 24.6%, and severe went from .7% to 5.1%.
• Those with lower incomes were 2.4 times more likely to be depressed. Those with less than $5,000 in savings were 1.5 more likely, and those with a higher number of stressors were 3.1 times more likely.
• Those who were married had the lowest rate of depression at 18.3% vs those who were widowed, divorced, or separated: 31.5%; 37.7% for those living with a partner, and 39.8% for those who were never married.

• Around 1 out of every 8 women will experience clinical depression in their lifetimes.
• Depression occurs most commonly in women between the ages of 24 and 44.
• Approximately 12 million women in the U.S. experience clinical depression each year.
• Women experience depression at twice the rate of men. There are many contributing factors, such as developmental, reproductive, hormonal, genetic, and other biological differences (e.g. premenstrual syndrome, childbirth, infertility, and menopause). Women also face stresses from social factors such as work, family, the roles and expectations of women as well as increased rates of sexual abuse and poverty.
• Women attempt suicide twice as often as men, though men are more likely to die by suicide.
• Depression is misdiagnosed in women 30% to 50% of the time.
• Fewer than half of women who experience depression seek care.

According to a Mental Health America survey:

• More than half of women believe it's normal for a woman to be depressed during menopause and treatment isn't necessary.
• Half of women believe depression is a normal part of ageing.
• Half of women believe it's normal for a woman to feel depressed two weeks after delivering a baby.
• More than half of women reported denial as the reason for not seeking treatment, while 41% gave embarrassment or shame as the reason.

• Rates of depression among the elderly are low, ranging from 1% to 5%.
• Rates are higher for those who require home healthcare, at 13.5%.
• The rate of depression for those in hospitals is 11.5%.
• 33% of widowers are depressed in the first month after the death of their spouse, and half of those remain depressed after one year.
• People aged 65 and older account for 20% of all suicide deaths, with white males being the largest in that group.
• The suicide rate for those 85 and older is almost 6 times the average rate for Americans.

According to the CDC, from 2013–2016:

• Asian adults had the lowest levels of depression at 3.1%.
• White: 7.9%.
• Hispanic: 8.2%.
• Black: 9.2%.
• Among all groups, men had significantly lower rates of depression compared to women.

• Around 2% of those treated for depression in an outpatient setting will die by suicide.
• Around 4% of those treated in an inpatient hospital setting die by suicide.
• Those treated for depression as inpatients after they attempted or thought about suicide die by suicide at a rate of 6%.
• 7% of men with a lifetime history of depression die by suicide; women only have a 1% rate.
• It's estimated that 60% of those who die by suicide had a mood disorder (major depression, bipolar disorder, dysthymia).
• Young people who kill themselves often have a substance abuse problem in addition to being depressed.

• In 2017, 9.4% of the U.S. population aged 12 to 17 had at least one major depressive episode with impairment, an estimated 2.3 million people.
• Of the teenagers with a major depressive episode, 70.77% had severe impairment.
• Girls 14–18 have consistently higher rates of depression than boys in the same age group.

Of the adults in the U.S. over age 18 who had a major depressive episode:

• 35% didn't receive treatment.
• 65% received a combination of care by a health professional and medication.
• 6% used medication only.
• 15% used a health professional only.
• 44% used a combination of medication and health professional care.

Of the teenagers who had a major depressive episode in 2017:

• 60.1% didn't receive treatment.
• 2.4% received medication only.
• 19.6% received care from a health care professional.
• 17.9% saw a health care professional and received treatment.

• Depression costs businesses over $100 billion per year.
• It causes $23 billion in lost workdays every year.
• 15.8% of adults from families below the federal poverty (FPL) line had depression. The rate is 3.5% among adults from families who are 400% over the FPL.
• The prevalence of depression decreases with increasing family income.
• Men with incomes above 400% of the FPL had the lowest rate of depression (2.3%), while women from families below the FLP had the highest rate (19.8%).

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