Light Therapy For Mood Disorders

Introduction

Mood disorders are psychiatric conditions with a prevalent emotional disturbance. They can be divided into:^1,2,3 

• Depressive disorders, characterised by low mood, such as major depressive disorder and seasonal affective disorder (SAD)
• Bipolar and related disorders, characterised by mood instability include bipolar disorders and cyclothymic disorder

Mood disorders usually start in late adolescence or early adulthood,³ but are commonly seen in children and adolescents, and it is estimated that 15% of them suffer from any mood disorder.² People with a mood disorder have higher chances of developing anxiety, substance abuse disorder, skipping work, and lower quality of life.²

What is light therapy and how it is done?

Light therapy is a type of therapy in which you are exposed to bright light for a determined period. It was first developed to treat seasonal affective disorder, but its use has expanded to other types of depression, bipolar disorder and some sleep disturbances.^4,5

Usually, the sessions are done:⁴

• With a special device, known as a light box, which contains fluorescent lamps
• Light intensities of 5,000–10,000 lux, at the level of the eye and a therapeutic distance of 60–80 cm,
• With a duration of 30 min using a light intensity of 10,000 lux, but it can be extended if the response is not sufficient

Be careful! Use a light box with a UV filter and do not stare directly into the light source, the light should reach the eye at an angle of 30–60°. Seek your doctor to know if this therapy is for you and follow it as prescribed.⁴ 

Mechanism of action on mood disorders

Resetting the body’s clock and daily rhythms

The exact mechanism of action of light therapy on mood disorders is not clear yet but may be related to the regulation of the body’s clock.^4,5 Most physiological functions of the body, have specific rhythmic changes during the day, such as your body temperature, sleep, and hormone secretion. Those rhythms are controlled by your body’s clock, which uses light as a signal to reset and be synchronized to the day-night cycle.^4,5

People with mood disorders may have alterations in their physiological rhythms, for example, they might sleep too early or too late compared to most people, or have reduced variations in their body temperature or hormone secretion throughout the day.⁴ Since light is important to adjust the body’s clock time, it could be a pathway through which light therapy helps with mood disorders.⁵

Melatonin

Light also influences the daily rhythm of melatonin, a hormone that induces sleep and also works as a “night signal” to the cells in your body. Melatonin is produced by the pineal gland, in a rhythm controlled by the body’s clock. Since light influences the body’s clock and also suppresses melatonin, it may improve this hormone variation during the day and normalized melatonin may improve sleep and mood disorders symptoms.^4,5

Serotonin

Serotonin is a neurotransmitter important for the regulation of emotions, behaviour and daily rhythms.⁴ In people with SAD, serotonin seems to be dysregulated because they can get better with medications that influence serotonin transmission and they show symptoms such as excessive sleepiness and carbohydrate craving, associated with this neurotransmitter dysfunction. Furthermore, studies have shown serotonin-related behaviours change in winter (when this condition usually occurs and light hours are reduced).^4,5 It's thought that light therapy may improve SAD by increasing the production and reducing the production of melatonin.^6,7

Effectiveness of light therapy for mood disorders

Seasonal affective disorder (SAD)

Seasonal affective disorder, is a form of depression that happens in the same season every year, usually in the winter, but can also occur during summer, although much less common.^8,9 Symptoms of SAD include:^4,8,9 

• Depressed mood for more than two weeks
• Loss of interest in typically enjoyable activities
• Feeling sad, hopeless or irritable
• Lack of concentration
• Changes in appetite
• Difficulty sleeping or sleeping too much
• Lack of energy
• Social withdrawal

Those symptoms of SAD are also common for people with major depression, but if you have SAD, you:⁹

• Tend to sleep more rather than have insomnia
• Tend to be more inactive rather than irritable
• May especially crave food rich in carbohydrates

It is estimated that SAD affects 5% of the population, but the percentage is higher in countries in the north. For example, Sweden has close to 8% of the cases, with young adults suffering from this condition most frequently.^8,9

Today, light therapy is the most common treatment for SAD and it has been used for more than 30 years.^4,9 Some studies showed it's effective, particularly if used in the morning and compared with other therapies it offers advantages such as it is fast-acting, non-invasive, and has minimal side-effects.⁹ However, there is no conclusive evidence regarding the effectiveness of light therapy compared to other types of therapies because most studies have a small number of patients and are very different from each other.^6,10 Other treatments for SAD include cognitive behaviour therapy, antidepressants, and increasing physical activity.⁸

Nonseasonal depression 

Nonseasonal depression, depression disorders not related to the changes of the seasons, may also benefit from light therapy. In general, depression is characterized by:^11,12

• Persistent depression
• Loss of pleasure or interest in commonly enjoyable activities
• Loss of energy
• Appetite and/or weight change
• Guilt feelings or thoughts of worthlessness
• Intellectual disability or restlessness
• Sometimes even self-harm or suicide

Depressive patients usually have alterations in physiological rhythms, such as:¹¹

• Mood swings throughout the day, with severe symptoms in the morning and relief at night
• Altered social rhythms
• Sleep disturbances, like waking up too early

Depression is one of the most common mental disorders, and in one year, 7% of the population is affected by this condition. It is also 1.5 to 3 times more common in women than in men.^11,12

Today, nonseasonal depression is mainly treated with antidepressants.^11,12 This type of medication can control depression-related symptoms but is associated with a risk of side effects including sexual dysfunction, blurred vision, tremors, urinary retention, insomnia, and low blood pressure.¹¹ Cognitive-behavioral therapy is a form of psychotherapy recommended for depression, but not all patients show improvement. A combination of antidepressants and cognitive-behavioural therapy has been associated with higher rates of improvement in depressive symptoms and quality of life.^11,12

Nowadays, light therapy is also recommended in combination with antidepressants.⁷ Some studies show that light therapy alone and light therapy combined with antidepressants help relieve depressive emotion, reduce anxiety, alleviate physical symptoms associated with depression, and improve sleep quality. However, more studies are needed to investigate whether light therapy is more effective and reliable than other alternative treatments.¹¹

Bipolar disorder

People with bipolar disorder have continuing and alternating episodes of:¹³

• Mania or hypomania - feeling very high and overactive or irritable
• Depression – feeling very low and apathetic, inactive

Bipolar disorder is difficult to diagnose because it has symptoms that are similar to other mental disorders, patients commonly have other conditions together, and they may not be aware of their conditions. Bipolar disorder occurs in 1% to 2% of the population and usually manifests either between 15 to 24 years or 45 to 54 years.^13,14 This mood disorder is one of the top 10 causes of disability in the world and patients with bipolar disorder have lower life expectancy because of a higher risk of suicide and other health issues, including cardiovascular, respiratory, and hormonal problems.¹³

There is no consensus of what is the best treatment for bipolar disorder, but it involves medication and psychosocial interventions. Still, some people don’t respond completely to the treatment and may have mood symptoms back again.¹³ Treatment is especially challenging for bipolar depression, compared to mania. Since light therapy can be recommended for treating depression, some studies investigated the effects of light therapy on bipolar depression.¹⁴

A review of studies concluded that there is positive but nonconclusive evidence that light therapy combined with medication reduces symptoms of bipolar depression and increases medication response.¹⁴ However, some researchers recommend using this treatment under medical supervision because of the risk of manic shift, that is, the patient shows symptoms such as irritability, psychomotor agitation, or sleep disorders. In this case, with close supervision, the duration of exposure can be adjusted rapidly.⁷

Potential side effects and risks

Usually, light therapy is well accepted and side effects are rare. Still, some patients can present:^4,6

• Headache
• Eyestrain (tired eyes)
• Changes to sight, like blurred vision
• Nausea
• Agitation or irritability
• Sleep problems (avoiding light therapy in the evening may help prevent it)

Those side effects can disappear spontaneously or after some therapy adjustments. Some patients with bipolar disorder may switch to hypomania during this therapy. Cases of irregularities in the menstrual cycle have been reported and the risk of suicidal thoughts may occasionally happen early in the treatment course. Furthermore, patients with eye problems (or family history) should consult their ophthalmologist before starting light therapy.⁴ 

Summary

Mood disorders are mental conditions characterized by emotional disturbances, including depressive and bipolar disorders.^1,2,3 Light therapy was initially developed to treat seasonal affective disorder (SAD), a type of depression, but today it can be recommended for other types of depression, bipolar disorder, and certain sleep disturbances. Light therapy may act by resetting the body's clock and daily rhythms, and influencing the secretion of melatonin and serotonin, which are affected in mood disorders.^4,5

Light therapy is a common treatment for SAD, offering advantages such as fast action, non-invasiveness, and minimal side effects. However, its effectiveness compared to other treatments is still inconclusive due to variations in study methodologies and the number of participants.^4,8,9 Light therapy may also help in alleviating depressive symptoms, reducing anxiety, and improving sleep quality in nonseasonal depression, but more studies are needed to investigate whether it is more effective than other alternative treatments.^11,12 In bipolar disorders, light therapy combined with medication may help reduce symptoms of bipolar depression, although its efficacy requires further investigation and caution is needed due to the risk of manic shifts.^7,13,14 

While light therapy is generally well-tolerated, potential side effects include headache, eyestrain, nausea, agitation, and sleep disturbances. Therefore, it is important to consult a doctor and an ophthalmologist for individuals with eye problems.^4,6In conclusion, light therapy may have some benefits as a treatment for mood disorders, particularly in SAD, but its efficacy and safety require further research.⁴