During the period of social isolation following the Covid-19 pandemic, mental health concerns have become more prominent. Many people are experiencing stress and anxiety, which can lead to depression.

    Depression is linked to certain behaviors associated with inflammation, such as poor eating habits and addiction to substances like alcohol, drugs, or smoking. Having an unhealthy diet, with low consumption of fruits and vegetables and a high intake of fast food or convenience food, may increase the risk of depression (1).

    A study by Black et al. found that lower levels of carotenoids like zeaxanthin/lutein, β-cryptoxanthin, lycopene, α-carotene, and β-carotene were associated with increased symptoms of depression. Importantly, this relationship remained even after considering the quality of the participants' diets. Since carotenoids are obtained exclusively through diet, the diet itself could be a significant factor influencing this relationship (2). Another study by Beydoun et al. reported that among the carotenoids examined, β-carotene, lutein, and zeaxanthin levels were inversely related to the occurrence of depressive symptoms among adults in the United States (3).

    Carotenoids have the potential to protect against the development of depression through various mechanisms. The most important point is that carotenoids are natural antioxidants that can effectively prevent oxidative damage. Antioxidants have been shown to have a neuroprotective effect by repairing the central nervous system and preventing neurodegeneration caused by oxidative stress.

    Humans cannot produce carotenoids on their own and must acquire them through their diet. Although there are around 700 identified carotenoids, only six are commonly found in the human diet and blood serum: α-carotene, β-carotene, lutein, zeaxanthin, lycopene, and β–cryptoxanthin. Furthermore, the typical human diet includes only about 40 different carotenoids. Carotenoids can be obtained from plant sources, such as fruits and vegetables, or from animal sources, such as egg yolk through the intake of plants.

    Carotenoids offer numerous benefits. They are primarily known for their antioxidant properties, as they can effectively neutralize reactive oxygen species. They may also have the potential in treating various types of cancer and regulating immune responses. The antioxidant and anti-inflammatory properties of carotenoids can enhance cognitive function by increasing neuronal efficiency and stabilizing lipid-protein bonds in neuronal membranes.

   Carotenoids have the potential to protect against depression through different mechanisms. Firstly, pro-inflammatory cytokines like Interleukin 6 (IL-6) and tumor necrosis factor (TNF) can impair the expression of brain-derived neurotrophic factor (BDNF), which can lead to the onset of depression. It has been observed that patients with depression often have lower levels of BDNF in their blood. Interestingly, studies have shown that β-carotene and zeaxanthin may reduce the expression of IL-6 and TNF. Carotenoids have also been investigated as potential inhibitors of BDNF through molecular docking studies, as BDNF is closely associated with depression. Recent docking results suggest that carotenoids could potentially allosterically activate BDNF. Based on these findings, dietary carotenoids could be utilized in the treatment of depressive symptoms (1).

    Secondly, the brain is particularly susceptible to oxidative stress due to its high oxygen consumption and the abundance of lipids. It is believed that the development of depression is closely linked to oxidative damage and an imbalance between pro-oxidants and antioxidants. Studies have indicated that individuals with depression often have elevated levels of 8-hydroxy-2’-deoxyguanosine, which is considered a marker of DNA damage caused by oxidative stress. These findings suggest a strong connection between depression and oxidative stress. Carotenoids have the ability to effectively remove reactive oxygen species and other free radicals. Therefore, considering their antioxidant and anti-inflammatory effects, it is expected that carotenoids could potentially have an antidepressant effect (1).

References:

1.            Rasmus, P., & Kozłowska, E. Antioxidant and Anti-Inflammatory Effects of Carotenoids in Mood Disorders: An Overview.  Antioxidants. 2023; 12(3). https://doi.org/10.3390/antiox12030676.

2.            Black C.N., Penninx B.W., Bot M., Odegaard A.O., Gross M.D., Matthews K.A., Jacobs D.R., Jr. Oxidative stress, anti-oxidants and the cross-sectional and longitudinal association with depressive symptoms: Results from the CARDIA study. Transl. Psychiatry. 2016;23:6, e743. doi: 10.1038/tp.2016.5.

3.            Beydoun M.A., Beydoun H.A., Boueiz A., Shroff M.R., Zonderman A.B. Antioxidant status and its association with elevated depressive symptoms among US adults: National Health and Nutrition Examination Surveys 2005–6. Br. J. Nutr. 2013;109:1714–1729. doi: 10.1017/S0007114512003467.

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