Subsyndromal depression (SSD) occurs when a person experiences depression symptoms that are not severe enough to meet the diagnostic criteria for other types of depression.

Subsyndromal describes a person experiencing symptoms that are insufficient for a formal clinical diagnosis of a condition. SSD can include minor, recurring depressive episodes.

People with the condition are at high risk for clinically significant major depression in the future.

This article further explains subsyndromal depression. It also goes over the symptoms, causes, and treatment of the condition.

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SSD is a “subthreshold” form of depression. Mental health professionals in the United States use the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR) for standard classification of mental health conditions.

Many individuals with subthreshold depression, such as SSD, and impaired functioning, do not meet the diagnostic criteria for depression.

The DSM-5-TR says a person has SSD if they have two or more (but fewer than five) symptoms of depression that have been present most of the time for at least two weeks and have impaired social functioning.

Read more about depression here.

Common symptoms of both SSD and major depression include:

  • feeling persistently sad, anxious, or “empty”
  • feeling irritable, frustrated, or restless
  • feeling guilty, worthless, or helpless
  • experiencing a loss of interest or pleasure in hobbies and activities
  • low energy, fatigue, or feeling slowed down
  • difficulty concentrating or making decisions and forgetfulness
  • insomnia
  • changes in appetite or unplanned weight changes
  • thoughts of death or suicide or suicide attempts

Suicide prevention

If you know someone at immediate risk of self-harm, suicide, or hurting another person:

  • Ask the tough question: “Are you considering suicide?”
  • Listen to the person without judgment.
  • Call 911 or the local emergency number, or text TALK to 741741 to communicate with a trained crisis counselor.
  • Stay with the person until professional help arrives.
  • Try to remove any weapons, medications, or other potentially harmful objects.

If you or someone you know is having thoughts of suicide, a prevention hotline can help. The 988 Suicide and Crisis Lifeline is available 24 hours a day at 988. During a crisis, people who are hard of hearing can use their preferred relay service or dial 711 then 988.

Find more links and local resources.

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People with SSD typically experience fewer symptoms than those with major depression. Additionally, people with SSD must experience these symptoms most of the time for at least two weeks. Those with major depression are more likely to experience consistent symptoms for a longer period of time.

There is no one definitive cause of SSD or major depression, but rather a series of risk factors that can increase a person’s risk of developing it.

Research suggests that genetic, biological, environmental, and psychological factors can play a role.

Genetic factors

Research shows that genetics and family history play a major role in depression. Additionally, several studies have identified the various ways that genetics plays a role.

The brain-derived neurotrophic factor (BDNF) also has a major part in depression. BDNF is a protein that plays an important role in the survival of neurons and growth. It also helps with memory and learning.

Additionally, there are links between major histocompatibility complex (MHC) region genes and depression. The MHC is a group of genes that create code for the proteins found on the surface of cells, which help the immune system recognize foreign substances.

Research also associates single nucleotide polymorphisms (SNPs) of genes involved in the tryptophan catabolites pathway with depression. SNPs are the most common genetic variations found in people. The tryptophan catabolites pathway is how the amino acid tryptophan interacts with different proteins and acids within the body.

Biological factors

These include genetics, the microbiome, inflammatory factors, stress and hypothalamic-pituitary-adrenal (HPA) axis dysfunction, and the kynurenine pathway.

HPA axis dysfunction is the chronic over-activation of the HPA axis as a result of long-term stress. The kynurenine pathway plays an important role in generating cellular energy within the body.

Additionally, the presence of a physical health condition can increase the risk of depression. There is also a significant relationship between depression and unhealthy habits, such as:

  • poor diet
  • little or infrequent exercise
  • alcohol consumption
  • smoking

Psychological factors

Determinants of depression include negative self-concept, sensitivity to rejection, neuroticism, rumination, and negative emotionality.

Social determinants also play a significant role in the development of depression, such as sociodemographics, social support, and adverse childhood experiences.

The DSM-5-TR outlines the following criteria to make a diagnosis of major depression:

  • depressed mood
  • loss of interest or pleasure in almost all activities
  • significant, unintentional weight loss/gain or decrease/increase in appetite
  • sleep disturbance (insomnia or hypersomnia)
  • psychomotor changes severe enough to be observable to others
  • tiredness, fatigue, or low energy, or completing routine tasks with decreased efficiency
  • a sense of worthlessness or excessive, inappropriate, or delusional guilt
  • impaired ability to think, concentrate, or make decisions — that a subjective report or others’ observation indicates
  • recurrent thoughts of death (not just fear of dying), suicidal ideation, or suicide attempts

A person must be experiencing five or more symptoms most of the time during a two-week period for a diagnosis of major depression. At least one symptom should also be a “depressed mood” or “loss of interest or pleasure.”

A diagnosis of subsyndromal depression means the person is experiencing two to five of the symptoms most of the time during a two-week period and the symptoms do meet the severity of major depression.

Potential challenges in diagnosis

Getting a formal diagnosis of SSD can be difficult. This may be because the DSM-5-TR does not explicitly identify subthreshold categories of depression.

A 2013 review associates SSD with an increased risk of psychosocial disability, major depression, dysthymia (persistent mild depression), social phobia, and generalized anxiety disorder (GAD). Additionally, research associates SSD with a decreased quality of life and increased societal and economic costs.

As a result, the researchers concluded that more research is vital on subthreshold categories of depression such as SSD. Furthermore, SSD should stand apart as a category and a doctor should treat it similarly to major depression, they said.

There are several treatments and management options for SSD. These include:

  • Medications: Typically, doctors treat depression with antidepressant medications, such as selective serotonin reuptake inhibitors (SSRIs).
  • Psychotherapy: Several studies have shown that therapies such as interpersonal therapy and cognitive behavioral therapy (CBT) can lead to improvements in functioning and decreases in depressive symptoms.
  • Lifestyle modifications: Research associates frequent exercise, a balanced diet, and optimal sleep duration with less frequency of depressed mood.

Although SSD does not have the same recognition as major depression, it is important to pay attention to symptoms and seek treatment when necessary because it has been shown to impact functioning and quality of life.

Early intervention is key in preventing long-term challenges and having success with treatment options.

Subsyndromal depression is a less commonly understood form of the condition. Researchers consider it to be subsyndromal because a person experiences fewer symptoms than a diagnosis of major depression requires.

Although the DSM-5-TR makes a distinction between subtypes of depression and major depression, the symptoms overlap. Furthermore, a person with SSD is at high risk for poor functioning, developing major depression, and other mental health conditions, such as general anxiety disorder.

Because the symptoms overlap, treatment options such as psychotherapy, medications, and lifestyle changes can have an impact on SSD.