The Immunomodulatory Effects of Sunlight

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Many believe that sunlight exposure has harmful effects, yet recent evidence suggests that sunlight may improve immune function. Beyond its ability to increase vitamin D levels in your body, researchers have demonstrated that sunlight can improve the motility of infection-fighting immune cells and discourage the spread of pathogens in hospital environments

Recent studies have indicated that sunlight exposure may have immunomodulatory effects and protect against infections, including acute respiratory infections such as influenza.[i]

Additionally, studies have shown that high levels of solar ultraviolet radiation (UVR) exposure are associated with lowered rates of allergies, autoimmune diseases and cancers.[ii],[iii] While these results are often attributed to increases in vitamin D, researchers have now demonstrated that sunlight exposure can improve immune function by improving the motility of killer T-cells.

In addition to these findings, researchers also point out that infectious outbreaks, including influenza, tend to happen more often during winter months when many people have little to no sunlight and UVR exposure.

Additional research from Columbia University suggests that UV light can kill even drug-resistant bacteria without inducing skin damage.[iv] Researchers believe there are two main facets that explain sunlight exposure's effect on immune function:

  • Increased Levels of Vitamin D

Sunlight exposure is widely known to increase vitamin D levels in your body. Skin cells absorb UVB radiation during skin exposure and convert it to vitamin D, which is metabolized in your liver and kidneys and used throughout your body to regulate calcium, increase beta-endorphins and stimulate the immune system.[v]

A deficiency of this important vitamin is linked to an increased risk of cancer, heart disease, obesity, depression, cognitive impairment, and bacterial and viral infections.[vi] Unlike other essential vitamins, since vitamin D is synthesized in your skin following UVB exposure, sunlight exposure is vital for improving vitamin D levels and subsequently improving immune function.[vii],[viii] If regular sunlight exposure isn't possible due to your climate or lifestyle, vitamin D supplementation may be useful.

  • Energization of Infection-Fighting T-Cells

Sunlight, particularly blue light and UV light contained in solar rays, energizes T-cells by triggering the production of hydrogen peroxide in these cells, which enhances their motility in the skin and improves their infection-fighting capabilities.[ix],[x]

Researchers theorize that the photosensitivity of T-cells may help to explain sunlight's positive effect on immune function and suggest blue-light therapy as a possible therapy for immuno-compromised patients.[xi]

In addition to these immune-boosting effects, researchers have found that sunlight may reduce the risk of infection in health care environments, as the majority of airborne microbes that cause infection cannot tolerate sunlight and are especially susceptible to direct (rather than diffused) sunlight.[xii]

Researchers theorize that time-cues from sunlight help to regulate biological rhythms, which may enhance immune function.[xiii] Additionally, they suggest that hospitals and health care facilities be designed to allow sunlight to reach occupants, as even sunlight through glass may discourage the survival and spread of pathogens.[xiv]

Additional Benefits of Sunlight Exposure

In addition to improving immune function, sunlight exposure is linked to a wide range of health benefits, including:

  • Increases Vitamin D Levels

High levels of vitamin D are important for improving inflammatory response, lowering blood pressure, increasing cognitive function and lowering the risk for certain cancers.[xv],[xvi] Researchers estimate that sunlight exposure accounts for 90% of most individual's vitamin D levels,[xvii] so if you're not getting much sunlight exposure, you're likely deficient.

  • Heals Skin Disorders

Various skin disorders, including eczema, psoriasis, acne and pityriasis rosea, improve through regular sunlight exposure.[xviii],[xix],[xx]

  • Improves Melatonin Production

Sun exposure improves melatonin production, a pineal hormone responsible for triggering your body's circadian rhythms and improving quality of sleep.[xxi] Melatonin also plays a key role in inflammation and infection and suppresses UVR-induced skin damage.[xxii]

  • May Improve Weight Loss

Animal studies have found that ongoing, low-level exposure to UV radiation can reduce weight gain and improve cardiovascular health in subjects fed a high-fat diet,[xxiii] perhaps by reducing certain aspects of metabolic dysfunction.

  • Provides Emotional Health Benefits

Ongoing, low-level exposure to sunlight is associated with improved mental health. In various studies, participants with depression and seasonal affective disorder experienced improved moods after sunlight therapy.[xxiv] Additionally, researchers have demonstrated that increased levels of vitamin D can improve depression and other mental disorders.[xxv]

  • Improves Cognitive Function

Recent studies have found a correlation between high levels of vitamin D and improved cognitive function.[xxvi]

Additionally, researchers have demonstrated that long-term, high levels of sun exposure are associated with better cognitive functioning, possibly because of the protective effect vitamin D has on brain cells and an increased production of serotonin and melatonin and improved circadian rhythms.[xxvii],[xxviii],[xxix]

The potential for sunlight exposure therapy is vast, and it's an affordable, natural and easily attainable way to improve immune function while boasting a wide range of additional benefits. To learn more about sunlight exposure's researched effects on cancer, psoriasis, cardiovascular disease, prenatal nutrition, mental disorders, skin care and more, please visit the sunlight exposure research database at


[i] Zeckhauser, R. J., & Slusky, D. (2018). Sunlight and Protection Against Influenza. The National Bureau of Economic Research. Retrieved from

[ii] Phan, T., Jaruga, B., Pingle, S. et al. Intrinsic Photosensitivity Enhances Motility of T Lymphocytes. Sci Rep 6, 39479 (2016).

[iii] Pathology 2012, Volume 44, Supplement 1, Page S40

[v] Dermatoendocrinol. 2013 Jan 1; 5(1): 51-108.

[vi] J Pharmacol Pharmacother. 2012 Apr-Jun; 3(2): 118-126.

[vii] Environ Health Perspect. 2008 Apr; 116(4): A160-A167.

[viii] J Pharmacol Pharmacother. 2012 Apr-Jun; 3(2): 118-126.

[ix] Phan, T., Jaruga, B., Pingle, S. et al. Intrinsic Photosensitivity Enhances Motility of T Lymphocytes. Sci Rep 6, 39479 (2016).

[xi] Phan, T., Jaruga, B., Pingle, S. et al. Intrinsic Photosensitivity Enhances Motility of T Lymphocytes. Sci Rep 6, 39479 (2016).

[xii] J Hosp Infect. 2013 Aug; 84(4): 271-282.

[xiii] J Hosp Infect. 2013 Aug; 84(4): 271-282.

[xiv] J Hosp Infect. 2013 Aug; 84(4): 271-282.

[xv] Jia J, Hu J, Huo X, Miao R, Zhang Y, Ma F. Effects of vitamin D supplementation on cognitive function and blood Aβ-related biomarkers in older adults with Alzheimer's disease: a randomised, double-blind, placebo-controlled trial. J Neurol Neurosurg Psychiatry. 2019;90(12):1347‐1352. doi:10.1136/jnnp-2018-320199

[xvi] Int J Mol Sci. 2018 Sep; 19(9): 2736.

[xvii] Issues Ment Health Nurs. Author manuscript; available in PMC 2011 Jun 1.

[xviii] Can Fam Physician. 2006 Apr 10; 52(4): 422-423.

[xix] Horio T. Skin disorders that improve by exposure to sunlight. Clin Dermatol. 1998;16(1):59‐65. doi:10.1016/s0738-081x(97)00170-3

[xx] Berg M. Epidemiological studies of the influence of sunlight on the skin. Photodermatol. 1989;6(2):80‐84.

[xxi] Environ Health Perspect. 2008 Apr; 116(4): A160-A167.

[xxii] Environ Health Perspect. 2008 Apr; 116(4): A160-A167.

[xxiii] Fleury N, Geldenhuys S, Gorman S. Sun Exposure and Its Effects on Human Health: Mechanisms through Which Sun Exposure Could Reduce the Risk of Developing Obesity and Cardiometabolic Dysfunction. Int J Environ Res Public Health. 2016;13(10):999. Published 2016 Oct 11. doi:10.3390/ijerph13100999

[xxiv] Environ Health. 2009; 8: 34.

[xxv] Issues Ment Health Nurs. Author manuscript; available in PMC 2011 Jun 1.

[xxvi] Int J Biometeorol. Author manuscript; available in PMC 2015 Apr 1.

[xxvii] Clin Interv Aging. 2018; 13: 2075-2082.

[xxviii] Environ Health. 2009; 8: 34.

[xxix] Int J Biometeorol. Author manuscript; available in PMC 2015 Apr 1.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of GreenMedInfo or its staff.

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