Introduction

Depression is a mood disturbance condition that lasts for more than two weeks in a row. As per the United States Department of Health and Human Services, the prevalence of depression is 8.7% in individuals aged between 18 and 25 years.1 Approximately, 264 million people worldwide suffer from this disorder.2 It is characterized by sadness, feelings of worthlessness or guilt, appetite changes, sleep problems, fatigue, loss of interest, aimless physical activities or slowed movements, thinking challenges, and worst of all, suicidal thoughts.3 Depression can also lead to reduced activities levels, hampering the ability to work and study. Suicide is the worst impact of depression, causing the deaths of; >700,000 people every year. Suicide is the fourth leading cause of death among 15-29-year-olds.4

Depression has several types, including depressive disorder (clinical depression), bipolar disorder (manic depression), persistent depressive disorder (dysthymia), and seasonal affective disorder (SAD).5 A potential cause of major depressive disorder (MDD) is an inflammatory reaction in the hippocampus.6 MDD can also occur due to bad life experiences. Child abuse, neglect, and loss increase the risk of MDD in adulthood.7 The exact cause of bipolar disorder (manic depression) is unknown, but several factors may contribute such as biological differences and genetics. Biological differences include circadian dysregulation of mood disorders, Circadian Locomotor Output Cycles Kaput (CLOCK) protein and Brain and Muscle ARNT-like Protein 1 (BMAL1), and pharmacological triggers like tricyclic antidepressants (TCAs).8 The existence of complex interactions between neurotransmitters and receptors that affect the brain’s chemical moods play a role in persistent depressive disorder. Neurotransmitters that affect mood include dopamine, epinephrine, norepinephrine, GABA, and glutamate,9 which are the neurotransmitters in question. The exact cause of SAD is unclear, but it may be due to chemical changes in the brain attributable to inadequate sunlight and shorter days. Additionally, melatonin may also be associated with SAD.10

Depression can be treated with antidepressants that are categorized into five groups, including tricyclic antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), monoamine oxidase inhibitors (MAOIs), serotonin-norepinephrine reuptake inhibitors, and non-TCA antidepressants.11 These treatments are effective;12,13 however, meta-analytical studies have found low remission rates,14 and antidepressants and placebo drugs only provide clinically significant differences in patients with upper-end severe depression. The reason for the skepticism with regard to the prescription of antidepressant drugs is their addictive effect. A study revealed that female patients and patients from ethnic minorities often choose complementary and alternative medicine (CAM) as the first step in treating depression.14 This skepticism refers to the trend of using CAM. One type of CAM approach includes natural products like dietary supplements (vitamins, minerals, and probiotics).15

Dietary supplements are orally consumed products, such as vitamins, herbs, minerals, amino acids, enzymes, metabolites, probiotics, and other substances for supplementing typical diets.16 Several dietary supplements have also been commonly used for reducing depression symptoms. For example, Kazemi et al17 explained that dietary supplementation, such as prebiotic use, significantly decreased the Beck Depression Inventory (BDI) scores compared with the placebo group, after eight weeks of intervention. Other dietary supplementations, such as polyunsaturated fatty acid (PUFA), vitamin D,18 B12,19 magnesium, zinc,20 and curcumin,21 have also been studied for their efficacy and effects as add-on supplements for depression treatment. In a review conducted by Hoffman et al,18 vitamin D and PUFA supplementation had complementarily positive effects on depressive symptoms, anxiety, and pain. Therefore, this review explored and summarized clinical study updates on dietary supplements’ types, dosages, and effectiveness to reduce symptoms of depression.