Sunlight affinity linked to lower depression rates in men

An analysis of data from the National Health and Nutrition Examination Survey (2009–2020) found that men with higher sunlight affinity tend to have fewer depressive symptoms. They also reported sleeping problems less often; however, their sleep durations tended to be shorter. The paper was published in PLOS ONE.

In the context of this study, “sunlight affinity” is a novel metric proposed by the authors to measure an individual’s tendency to seek and enjoy natural sunlight. It combines psychological factors (preference for sun) and behavioral factors (actual time spent outdoors). Generally, the drive for sunlight is influenced by biological factors such as circadian rhythms, melatonin suppression, and serotonin regulation.

People with high sunlight affinity tend to report improved mood, energy, and alertness during bright daytime conditions. This tendency is partly genetic but is also shaped by developmental experiences, climate, and cultural habits. Conversely, low sunlight affinity may be associated with discomfort in bright light or a preference for dim environments.

While sunlight affinity is conceptually related to light sensitivity and seasonal affective patterns, it is not a clinical diagnosis. In environmental psychology, it helps explain preferences for outdoor activities and sunlit living or working spaces. In health contexts, moderate sunlight affinity can promote behaviors that support vitamin D synthesis and circadian stability.

Lead author Haifeng Liu and his colleagues investigated the associations between sunlight affinity and symptoms of depression and sleep disorders in U.S. men. They examined two dimensions of sunlight affinity: sunlight preference (how often a person chooses to stay in the sun versus the shade) and sunlight exposure duration (how much time a person spends outdoors). They noted that while recent findings indicate light therapy might help reduce depressive symptoms and improve sleep, the impact of natural sunlight exposure remains underexplored.

The authors analyzed data from 7,306 men who participated in the National Health and Nutrition Examination Survey (NHANES) between 2009 and 2020. NHANES is a continuous, nationally representative U.S. program that combines interviews, physical examinations, and laboratory tests to assess the health, nutritional status, and disease prevalence of the civilian, noninstitutionalized population.

The researchers selected males aged 20–59 years who provided all the necessary data. These individuals completed assessments for sunlight affinity, depressive symptoms (using the Patient Health Questionnaire-9), sleep disorder symptoms (answering, “Have you ever told a doctor or other health professional that you have trouble sleeping?”), and sleep duration.

Sunlight affinity was assessed by asking participants, “When you go outside on a very sunny day for more than one hour, how often do you stay in the shade?” and by asking them to report the time they spent outdoors between 9:00 AM and 5:00 PM over the previous 30 days.

The results showed that participants with a higher preference for sunlight and longer exposure durations tended to have fewer depressive symptoms. They also reported sleep problems less often, though their total sleep time tended to be shorter.

“This study revealed that sunlight affinity was inversely associated with depression and trouble sleeping and positively associated with short sleep in males. Further longitudinal studies are needed to confirm causality,” the authors concluded.

The study sheds light on the links between sunlight affinity, depression, and sleep problems. However, it should be noted that the cross-sectional study design does not allow for causal inferences. Additionally, all study data were based on self-reports, leaving room for reporting bias to have affected the results.

The paper, “Associations of sunlight affinity with depression and sleep disorders in American males: Evidence from NHANES 2009–2020,” was authored by Haifeng Liu, Jia Yang, Tiejun Liu, and Weimin Zhao.