Negative Association Between Sun Exposure and Depression: A Cross-Sectional Analysis of the NHANES 2011-2018 In the United States

Background

According to the World Health Organization (WHO), more than 350 million people worldwide have symptoms of depression, and people with depression deserve more care. As reported in a study by Munoz, R F, et al., depression is expected to become the second largest community health problem in the world [1]. Depression, as a mental disorder, can have a negative impact on people’s thinking and behavior, and cause adverse consequences for people’s mental health and physical health. For example, people with depression have mental health problems such as suicidal thoughts and loss of interest in things, and physical health problems such as obesity and insomnia [2].

Depression, as a serious disabling disease, exists widely in the world. The United States is greatly affected by major depressive disorder, and its direct consequence is an increased socio-economic burden [3]. In 2012, the socioeconomic burden of major depression in the United States exceeded the economic burden of cancer ($131 billion) and diabetes ($173 billion) in the United States, amounting to an estimated $188 billion [4]. In addition to the United States, other countries in the world also face the health challenge of depression [5]. The German Social Insurance Agency has reported an increase in early retirement and medical service provision, an increase in the frequency of depression, and an increase in healthcare costs, influenced by the loss of working days [6,7]. Therefore, analysis of the causes and potential influencing factors of depression is the key to effective prevention and treatment of depression.

In recent years, due to the destruction of the atmospheric ozone layer, the ultraviolet rays reaching the surface have increased, and too much or too long sunlight exposure may cause skin diseases [8,9], resulting in excessive sun protection and reduced outdoor activities. However, studies have reported negative effects on cardiovascular disease, bone disease, and autoimmune diseases due to insufficient sun exposure or vitamin D intake [10-13]. At the same time, insufficient sun exposure can also lead to mental health disorders such as depression and anxiety. Sun exposure has been used as a way to alleviate a variety of conditions, such as lowering blood pressure, improving brain function and treating skin diseases. Sunlight exposure is beneficial to mental health. Sansone, R A, et al., [14] have discussed the relationship between psychopathology and sunlight.

In this study, we designed a cross-sectional study using data from the National Health and Nutrition Examination Survey (NHANES) to analyze the association between sun exposure and depression in order to provide advice on depression prevention and treatment for public health and health issues.

Methods and Materials

Objects

The National Health and Nutrition Examination Survey (NHANES) is a cross-sectional survey designed to assess the health and nutrition status of adults and children in the United States [15]. In this study, a total of 11682 representative samples of NHANES aged between 20 and 59 from 2011 to 2018 were selected. NHANES covers about 15,000 households, all of which are U.S. residents who have lived in the United States for at least two months. The protocol and secondary analysis of the data were approved by the NCHS Ethics Review Board, and all participants were informed of the study’s purpose, risks, and benefits and provided written notice of consent [16].

Covariables

In this study, we included demographic variables such as gender, age, race, education, marital status, income-poverty ratio, and current health status. Among the counting variables, gender is divided into male and female; Ethnically divided into Mexican Americans, other Hispanics, non-Hispanic whites, non-Hispanic blacks, non-Hispanic Asians, and other races; The education level is divided into high school education, high school education and high school education; Marital status is divided into cohabitation, married living alone (widowed, divorced, separated) and never married; Current health status is classified as excellent, good or poor. The age range of the measurement variables is 20-59 years old; The income-poverty ratio, which ranges from 0.00 to 5.00, is a poverty guideline divided by household income for the year surveyed. In this study, the poverty ratio was used to create two income conditions, poor (<1.3) and middle income (≥1.3) [17].

Sunlight Exposure Assessment

Sun exposure data were extracted from the Dermatology Questionnaire (DEQ), which included data from individual interviews about sun exposure and sun protection behaviors. We took the question “On a sunny day, when you go out for more than an hour, how much time do you spend in the shade?” (DEQ034A) “to assess the intensity of participants’ sun exposure levels. Participants responded on a scale of six: 1= never going out in the sun, 2= always, 3= most of the time, 4= sometimes, 5= rarely, and 6= never.

Depression Assessment

Depression data were extracted from the Depression Screening Questionnaire (DPQ), also known as the Patient Health Questionnaire. These included nine depression screening questions to assess the frequency of depressive symptoms in the sample over the past two weeks. Scores for each question response category “not at all,” “some days,” “more than half,” and “almost every day” ranged from 0 to 3 points [18,19]. For those who answered the question completely, a total score (ranging from 0 to 27) was calculated. In this study, we defined depression as a counting variable and divided it into two groups, 1= non-depressed group (0-4 points) and 2= depressed group (5-27 points). (19)

Quality Control

To ensure data quality, the data obtained by NHANES is presented by trained interviewers in a mobile Test Center (MEC), using a computer Assisted Personal Interview (CAPI) system as part of the MEC interview. CAPI systems are programmed with built-in consistency checks to reduce data entry errors.

Statistical Analysis

In this study, Microsoft Excel2010 was used to extract and merge the original data, excluding missing and useless (rejected, unknown) data. The database included information on demographics, sun exposure, and depression among U.S. adults aged 20 to 59 years (5,681 males, 6,601 females, mean age 39.32±11.523). According to the purpose of the study, we tested the statistical significance of covariates between the “non-depressed” and “depressed” groups. Chi-square test was used for counting variables and rank sum test was used for measuring variables. We used a binary Logistic regression model to analyze the relationship between “sun exposure” and “depression.” All data were analyzed using Statistical Product and Service Solutions (SPSS) version 26.0, with P<0.05 considered statistically significant (two-sided test). Variables that were statistically significant in the univariate analysis were included in the stepwise binary Logistic regression analysis. A-entry=0.05 and a-exit=0.10 were used to select and exclude confounding variables.

With sun exposure as the independent variable and depression as the dependent variable, all covariables (P<0.001) were statistically significant in the univariate analysis. In analyzing the relationship between sun exposure and depression, the following models were established to exclude the influence of confounding variables: Model I: Only the independent variable sun exposure was adjusted. Model II: Demographic variables (gender, age, race, education, marital status, income-poverty ratio, and current health status) were adjusted for the independent variables in Model I.

Results

Demographic Characteristics

The study included 11,682 adults aged 20 to 59 years from the National Health and Nutrition Examination Survey during the 2011-2018 cycle. They completed data collection on demographics, sun exposure and depression. The depressed and non-depressed groups were statistically significant in terms of sex (P<0.001), age (P<0.001), race (P<0.001), education level (P<0.001), marital status (P<0.001), income-poverty ratio (P<0.001), and current health status (P<0.001) (See Table 1).

Table 1: Demographic characteristics of adults aged 20-59 years with depression.

Note*: a Chi-square test, b Rank sum test, *P<0.05, **P<0.01, ***P<0.001.

Relationship Between Sunlight Exposure and Depression

In logistic regression analysis, model I (without excluding any confounding variables) showed that the odds ratio (OR) of sun exposure to depression was 0.866(95%Cl :0.833-0.900, P < 0.001). Model II (excluding demographic variables) showed an odds ratio (OR) of 0.945(95%Cl :0.906-0.985, P < 0.05). The findings suggest that after adjusting for confounders, sun exposure is a protective factor for depression, and sun exposure can effectively reduce people’s risk of developing depression (See Table 2).

Table 2: Logistic regression analysis results of sun exposure and depression.

A Only the independent variable of sunlight exposure was adjusted. b Adjustments were made for independent variables in Model I plus demographic variables (sex, age, race, education, marital status, income-poverty ratio, and current health status).

Discussion

Using a binary Logistic regression analysis of NHANES data from 2011-2018, we found an independent association between sun exposure and depression in American adults aged 20-59 years. For every increase in the intensity of sunlight exposure, the risk of depression was reduced by 5.5%. We discuss the relationship between sun exposure and depression in more depth below.

Sun Exposure and Depression

Our findings are consistent with many previous studies showing that the longer the time spent in the sun, the lower the risk of depression. In a cross-sectional study of Chinese college students, the longer the reported duration of sun exposure or outdoor activity, the lower the score on the Depression Scale (CES-D) [20] In a cross-sectional survey of older Chinese women assessed using the Zung Self-rated Depression Scale (SDS), increased sun exposure was associated with a lower prevalence of depressive symptoms in older women in a logistic regression model [21]. In prospective follow- up of middle-aged people with multiple sclerosis in Australia, sun exposure was reported to be negatively associated with depression scores [22]. In a study of sun exposure and psychosocial stress in Korean adults, it was shown that the less time participants were exposed to sunlight, the higher psychosocial stress was, which predicted an increased likelihood of developing depressive mood [23]. In the study of a special group of people who are not exposed to sunlight at work, researchers studied the sun exposure and mental health of operating room nurses and found that operating room nurses showed worse mental health than other groups, which also means that the risk of depression symptoms is higher. Our results are consistent with previous research on sun exposure and depression. However, we cannot limit ourselves to the findings and would like to explore further why sun exposure is positively associated with depression.

The relationship between sunlight exposure and depression was analyzed from the biological perspective. Proper sun exposure will stimulate the skin to synthesize vitamin D3, and vitamin D3 has an improving effect on human immune function, can regulate inflammatory response, affect calcium homeostasis [24,25]. Insufficient sunlight exposure leads to decreased production of vitamin D3, and insufficient levels of vitamin D3 in the human body are associated with a variety of diseases, such as cardiovascular disease, metabolic syndrome, osteoporosis, rickets, immune diseases, kidney diseases, and psychiatric disorders [26-29]. Exposure to sunlight stimulates intrinsically sensitive retinal ganglion cells, thereby affecting melatonin secretion and balancing the circadian rhythm. In a study by Dowling, et al., [30] researchers used artificial light therapy that mimics sunlight in Alzheimer’s patients and reported significant improvements in insomnia, sleep disturbances, and sleepwalking. Therefore, we believe that sun exposure also has an important effect on sleep cycle and sleep quality [31], and sleep cycle and sleep quality may have an impact on the prevention or treatment of depression. Sun exposure has an impact on serotonin [32], a mood-boosting neurotransmitter, and a lack of sun exposure leads to decreased serotonin production, which can lead to negative emotions such as depression. In the rehabilitation training using light therapy, Tsai, et al., ‘s research report showed that it can alleviate depression in the elderly, which means that a variety of light waves of sunlight have a positive effect on depression [33].

The relationship between sunlight exposure and depression was analyzed from the perspective of psychology. In psychological research, we can find that self-denial, negative emotions and low emotional clarity are related to depression. When it comes to depression, one of the determinants that has received a lot of attention in mental health research is rumination. Rumination refers to when an individual experiences stress or is negatively affected, he spontaneously thinks repeatedly about the causes and consequences of emotions, instead of actively facing and solving problems. It is a mediating factor and risk factor for depression [34]. Leanne Trick, et al., ‘s findings suggest that rumination is an important independent predictor of depression, and that the relationship between rumination and depression has been explained in part by “inadequate problem solving skills” and “inadequate social support” [35]. Outdoor sports, rock climbing, surfing, cliff downhill and other challenging and exciting extreme sports can stimulate people’s resilience and perseverance, give people a sense of accomplishment and satisfaction. This kind of outdoor exercise helps people reduce depression and anxiety, and has a positive effect on mental and spiritual status. We think that people with more sun exposure are more likely to be willing to participate in these kinds of extreme outdoor activities. Not only are they exposed to sunlight during these outdoor activities, but they are also able to develop their problem-solving skills, gain social support, and experience positive emotions, thereby reducing the risk of depression.

The relationship between sunlight exposure and depression was analyzed from a sociological perspective. Sociological factors, including the factors people experience in life, entertainment, study and work [36], such as social status, different life experiences, educational background and economic pressure, are all related to depression. From a sociological perspective, interpersonal relationship difficulties are associated with depression [37], and good social relationships are protective factors for depression. Outdoor team sports such as football, rugby and beach volleyball are conducive to the establishment of good interpersonal relationships between people. Therefore, we recommend that whether or not people with depression should carry out appropriate physical activity in the sun in their daily life. On the one hand, it can physiologically ensure that mood-boosting neurotransmitters and vitamin D are maintained at healthy levels; On the other hand, it can establish good interpersonal relationships to prevent or improve depression. For the relationship between sun exposure and depression, we can explain to some extent that the lack of outdoor activities and sedentary behavior for a long time, resulting in lack of sun exposure and depression. Less outdoor activity leads to less sunlight exposure, which also means less physical activity. In the systematic review and meta-analysis of the association between physical activity and depression by Pearce M, et al., significant benefits of physical activity on mental health were noted, even at levels below public health recommendations [38].

After discussion, this study suggests that depression can be prevented or treated with appropriate sunlight exposure. In particular, participation in outdoor physical activities to increase sunlight exposure is a more advocated way.

Limitations

There are some limitations in this study. First of all, the data of this study came from the National Health and Nutrition Examination Center of the United States, and the samples were all American citizens, so the applicability of the current research results to other countries and regions remains to be studied. In future studies, we will collect data from other countries and regions to demonstrate the results of this study. Second, this study only analyzed data from adults aged 20-59 in the United States, and we will expand the study population to include children, adolescents, and the elderly in future studies. Finally, we mentioned that outdoor physical activity may be a protective factor for the prevention or treatment of depression in the discussion of the article. In future studies, we hope to list physical activity as a separate factor and discuss the relationship between sunlight exposure, physical activity and depression in more depth and detail.

Conclusions

As a serious disabling disease, depression has caused harm to many citizens in the world. The aim of this study was to determine the effect of sun exposure on depression in American adults and to conclude that sun exposure is a protective factor for depression. Future studies need to consider the feasibility of increasing sun exposure by engaging in outdoor physical activity to prevent or treat depression.

Declarations

Ethics Approval and Consent to Participate

All procedures performed in the study were in accordance with the Declaration of Helsinki. The study protocols for NHANES were approved by the National Center for Health Statistics (NCHS) Research Ethics Review Board (Protocol#2017-1). All adult participants provided written notification of consent before participating in the study.

Consent for Publication

Not applicable.

Availability of Data and Materials

The datasets generated and/or analysed during the current study are available in the [NHANES] repository, [NHANES Questionnaires, Datasets, and Related Documentation (cdc.gov)]. Raw data supporting the obtained results are available at the corresponding author.

Author Contributions

YC and JZ conceived and designed the study. YC organized the database, performed the statistical analysis and wrote the manuscript. Linguist RF confirmed the accuracy of the written language. YC, JZ and RF revised the manuscript. All authors edited, revised, and certified the final version of this manuscript.

Funding

This study were supported by the 2019 Sports Research Project of Henan Province Sports Bureau (Grants No. 2019052) and the 2020 General Project of Henan Province Education Science “13th Five-Year Plan” (Grants No. 2020YB0014).

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

We would like to thank all the staff and participants of the National Health and Nutrition Examination Survey 2011-2018 cycles for their valuable contributions. Any interpretation or conclusion related to this manuscript does not represent the views of the NHANES. We would also like to thank the editors and reviewers for their valuable and constructive comments to help us improve the manuscript.

References

• Muñoz RF, Beardslee WR, Leykin Y (2012) Major depression can be prevented. Am psychol 67(4): 285-295.
• (2013) Diagnostic and Statistical Manual of Mental Disorder. Am Psychiatr Association.
• Hasin DS, Servet AL, Meyers JL, Saha TD, Ruan WJ, et al. (2018) Epidemiology of Adult DSM-5 Major Depressive Disorder and Its Specifiers in the United States. JAMA Psychiatry 75(4): 336-346.
• Mrazek DA, Hornberger JC, Altar CA, Degtiar I (2014) A review of the clinical, economic, and societal burden of treatment-resistant depression: 1996-2013. Psychiatr Serv 65(8): 977-987.
• Nübel J, Guhn A, Müllender S, Le HD, Cohrdes C, et al. (2020) Persistent depressive disorder across the adult lifespan: results from clinical and population-based surveys in Germany. BMC Psychiatry 20(1): 58.
• (2015) Statistisches Bundesamt (Destatis) Gesundheit: Krankheitskosten.
• Gerste B, Roick C (2014) Prävalenz und Inzidenz sowie Versorgung depressiver Erkrankungen in Deutschland - Eine Analyse auf Basis der in Routinedaten dokumentierten Depressionsdiagnosen. In: Klauber J, Günster C, Gerste B, Robra BP, Schmacke N, editors. Versorgungs-report 2013/2014. Stuttgart: Schattauer 21-54.
• Armstrong BK, Kricker A (2001) The epidemiology of UV induced skin cancer. J photochem Photobiol B 63(1-3): 8-18.
• Savoye I, Olsen CM, Whiteman DC, Bijon A, Wald L, et al. (2018) Patterns of Ultraviolet Radiation Exposure and Skin Cancer Risk: the E3N-SunExp Study. J Epidemiol 28(1): 27-33.
• Lindqvist PG, Olsson H, Landin Olsson M (2010) Are active sun exposure habits related to lowering risk of type 2 diabetes mellitus in women, a prospective cohort study? Diabetes Res Clin Pract 90(1): 109-114.
• Holick MF (2011) Vitamin D deficiency in 2010: health benefits of vitamin D and sunlight: a D-bate. Nat Rev Endocrinol 7(2): 73-75.
• Bellan M, Sainaghi PP, Pirisi M (2017). Role of Vitamin D in Rheumatoid Arthritis. Adv Exp Med Biol 996: 155-168.
• Jiang X, Alfredsson L (2020) Modifiable environmental exposure and risk of rheumatoid arthritis-current evidence from genetic studies. Arthritis Res Therapy 22(1): 154.
• Sansone RA, Sansone LA (2013) Sunshine, serotonin, and skin: a partial explanation for seasonal patterns in psychopathology? Innov Clin Neurosci 10(7-8): 20-24.
• Cao C, Liu Q, Yang L, Zheng X, Lan P, et al. (2020) Handgrip strength is associated with suicidal thoughts in men: Cross-sectional analyses from NHANES. Scand J Med Sci Sports 30(1): 92-99.
• Yang L, Cao C, Kantor ED, Nguyen LH, Zheng X, et al. (2019) Trends in Sedentary Behavior Among the US Population, 2001-2016. JAMA 321(16): 1587-1597.
• Fadeyev K, Nagao Sato S, Reicks M (2021) Nutrient and Food Group Intakes among U.S. Children (2-5 Years) Differ by Family Income to Poverty Ratio, NHANES 2011-2018. Int J Environ Res Public Health 18(22): 11938.
• Kroenke K, Spitzer RL, Williams JB (2002) The PHQ-15: validity of a new measure for evaluating the severity of somatic symptoms. Psychosom Med 64(2): 258-266.
• Kroenke K, Spitzer RL, Williams JB (2001) The PHQ-9: validity of a brief depression severity measure. J Gen Intern Med 16(9): 606-613.
• Xu Y, Qi J, Yang Y, Wen X (2016) The contribution of lifestyle factors to depressive symptoms: A cross-sectional study in Chinese college students. Psychiatry research 245: 243-249.
• Cui Y, Gong Q, Huang C, Guo F, Li W, et al. (2021) The relationship between sunlight exposure duration and depressive symptoms: A cross-sectional study on elderly Chinese women. PloS one 16(7): e0254856.
• Knippenberg S, Damoiseaux J, Bol Y, Hupperts R, Taylor BV, et al. (2014) Higher levels of reported sun exposure, and not vitamin D status, are associated with less depressive symptoms and fatigue in multiple sclerosis. Acta neurologica Scandinavica 129(2): 123-131.
• Hwang HJ, Choi YJ, Hong D (2022) The Association between Self-Rated Health Status, Psychosocial Stress, Eating Behaviors, and Food Intake According to the Level of Sunlight Exposure in Korean Adults. Int j environ res public health 20(1): 262.
• Holick MF (2004) Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers, and cardiovascular disease. Am j clin nutr 80(6 Suppl): 1678S-1688S.
• Verhoeven V, Vanpuyenbroeck K, Lopez Hartmann M, Wens J, Remmen R (2012) Walk on the sunny side of life--epidemiology of hypovitaminosis D and mental health in elderly nursing home residents. J Nutr Health Aging 16(4): 417-420.
• Wacker M, Holick MF (2013) Sunlight and Vitamin D: A global perspective for health. Dermatoendocrinol 5(1): 51-108.
• Hoel DG, de Gruijl FR (2018) Sun Exposure Public Health Directives. Int j environ res public health 15(12): 2794.
• Alfredsson L, Armstrong BK, Butterfield DA, Chowdhury R, de Gruijl F R, et al. (2020) Insufficient Sun Exposure Has Become a Real Public Health Problem. Int j environ res public health 17(14): 5014.
• Gallagher JC (2013) Vitamin D and aging. Endocrinol Metab Clin North Am 42(2): 319-332.
• Dowling GA, Hubbard EM, Mastick J, Luxenberg JS, Burr RL, et al. (2005) Effect of morning bright light treatment for rest-activity disruption in institutionalized patients with severe Alzheimer's disease. Int psychogeriatr 17(2): 221-236.
• Dumont M, Beaulieu C (2007) Light exposure in the natural environment: relevance to mood and sleep disorders. Sleep med 8(6): 557-565.
• Lambert GW, Reid C, Kaye DM, Jennings GL, Esler MD (2002) Effect of sunlight and season on serotonin turnover in the brain. Lancet 360(9348): 1840-1842.
• Tsai YF, Wong TK, Juang YY, Tsai HH (2004) The effects of light therapy on depressed elders. Int j geriatr psychiatry 19(6): 545-548.
• DeJong H, Fox E, Stein A (2019) Does rumination mediate the relationship between attentional control and symptoms of depression?. J Behav Ther Exp Psychiatry 63: 28-35.
• Trick L, Watkins ER, Henley W, Gandhi MM, Dickens C (2019) Perseverative negative thinking predicts depression in people with acute coronary syndrome. Gen hosp psychiatry 61: 16-25.
• Remes O, Mendes JF, Templeton P (2021) Biological, Psychological, and Social Determinants of Depression: A Review of Recent Literature. Brain sci 11(12): 1633.
• Filia K, Eastwood O, Herniman S, Badcock P (2021) Facilitating improvements in young people's social relationships to prevent or treat depression: A review of empirically supported interventions. Transl psychiatry 11(1): 305.
• Pearce M, Garcia L, Abbas A, Strain T, Schuch FB, et al. (2022) Association Between Physical Activity and Risk of Depression: A Systematic Review and Meta-analysis. JAMA psychiatry 79(6): 550-559.