Daily guidelines for safe, beneficial sun exposure that support mitochondrial health, vitamin D production, and circadian rhythm regulation
By Roger Seheult, MD - Quadruple Board Certified Physician and Co-Founder of MedCram.com
1 Morning Light (Eyes)
🔹 When: Within first hour after waking
🔹 Duration: 1–20 minutes, depending on cloud cover and brightness
🔹 How: Look toward but not at the sun (no sunglasses, avoid direct staring)
🔹 Benefits: Anchors circadian rhythm, boosts alertness and mood
🔬Evidence 1, 2, 3, 4, 5, 6, 7, 8, 9
2 Infrared / Near-Infrared Light (Skin)
🔹 When: Anytime outdoors, ideally early morning or late afternoon (UV Index ≤ 5)
🔹 Duration: 15+ minutes daily
🔹 Notes: Infrared penetrates clothing, is enhanced by greenery, and can be safely absorbed in the shade
🔹 Benefits: Supports mitochondrial ATP production, anti-inflammation, cellular health
🔬Evidence 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 50, 51, 52, 53, 54, 55
3 Vitamin D Production (UVB)
🔹 Best time: Midday (11am–2pm) when UVB is highest
🔹 Exposure target: ≥ 35% body surface area (arms and legs)
| Skin Type | Spring/Summer Exposure | Winter/High Latitude |
|---|---|---|
| I–II | 5–10 min mid-day x3/week | Supplement needed |
| III-IV | 15–20 min mid-day x3/week |
Supplement needed |
| V-VI | 30–60 min mid-day daily | Supplement needed |
🔹 Adjustments:
- Fitzpatrick I–II: Shortest exposure, highest burn risk
- Fitzpatrick V–VI: Require longer exposure to synthesize equivalent vitamin D 2.5x and 4.0x respectively
- Older age, darker skin, winter → may require supplementation
- Vitamin D is fat-soluble and stored, so missing some days is acceptable.
🔬Evidence 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34
Resources and References:
Figure out your skin type: https://www.skincancer.org/blog/are-you-at-risk-for-skin-cancer/
📱 Use the UV Index
- UV ≤ 5: Likely safe for brief unprotected exposure
- UV > 5: Protect skin with shade, clothing, hats, or mineral sunscreen
Other Apps to guide timing: Shadowmap, D Minder, EPA UV Index, SunSense UV tracker for personalized estimated exposure timing
🚫 What to Avoid
⛔ >15 minutes unprotected in strong sun (UV Index >5) – varies by skin type
⛔ Relying on indoor sunlight – glass blocks ~95% of UVB and infrared
⛔ Applying sunscreen before short, intentional vitamin D exposure
⛔ Assuming darker skin = sun immunity – higher melanin protects but does not prevent burns and requires longer exposure
🔬Evidence: 31, 32, 33, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49
References
1 Morning bright light improves nocturnal sleep and next morning alertness in office occupants: An electroencephalography study (2022). These findings support existing evidence that morning bright light could function as an enhancer of sleep and alertness for office occupants. https://pubmed.ncbi.nlm.nih.gov/36058557/
2 Psychophysiological effects of early morning bright light exposure in young women (1990). In comparison with a dim light exposure, the bright light resulted in increased motor activity during waking, in earlier peak of subjective alertness, and an advanced phase position of the circadian system. https://pubmed.ncbi.nlm.nih.gov/2255748/
3 Intense illumination in the morning hours improved mood and alertness but not mental performance (2014). These results suggest that brief exposure to bright light in the morning hours can improve subjective measures of mood and alertness. https://pubmed.ncbi.nlm.nih.gov/25106786/
4 Awakening effects of blue-enriched morning light exposure on university students' physiological and subjective responses (2019). Exposure to blue-enriched white light significantly improved subjective perception of alertness, mood, and visual comfort. https://pubmed.ncbi.nlm.nih.gov/30674951/
5 Transition from dim to bright light in the morning induces cortisol response and increases heart rate variability in humans (2001). The early morning transition from dim to bright light suppressed melatonin secretion, induced an immediate, greater than 50% elevation of cortisol levels. https://pubmed.ncbi.nlm.nih.gov/11231993/
6 Delayed Sleep in Winter Related to Natural Daylight Exposure among Arctic Dayworkers (2018). Increased morning light exposure was associated with earlier mid-sleep (p < 0.001), while increased evening light exposure was associated with delayed mid-sleep. https://pubmed.ncbi.nlm.nih.gov/33089157/
7 CME: Light Therapy: Why, What, for Whom, How, and When (2022). Light impacts the timing and stability of circadian rhythms as expressed in sleep, mood, alertness, and cognition. https://pubmed.ncbi.nlm.nih.gov/35105211/
8 Effects of dawn simulation on markers of sleep inertia and post-waking performance in humans (2014). These data provide the first evidence that light exposure during the last 30 min of habitual sleep can increase subjective alertness and improve both cognitive and vigilance performance after waking. https://pubmed.ncbi.nlm.nih.gov/24509892/
9 Effects of light on human circadian rhythms, sleep and mood (2019). In sum, research seems to agree that daylight (at high intensities) is beneficial for sleep, circadian rhythms, and mood. https://pmc.ncbi.nlm.nih.gov/articles/PMC6751071/
10 Effects of Near-Infrared Light on Well-Being and Health in Human Subjects with Mild Sleep-Related Complaints: A Double-Blind, Randomized, Placebo-Controlled Study - https://pmc.ncbi.nlm.nih.gov/articles/PMC9855677/
11 Near-infrared light increases ATP, extends lifespan and improves mobility in aged Drosophila melanogaster - https://pmc.ncbi.nlm.nih.gov/articles/PMC4387504/
12 Mechanisms and applications of the anti-inflammatory effects of photobiomodulation - https://pmc.ncbi.nlm.nih.gov/articles/PMC5523874/
13 Unlocking the Power of Light on the Skin: A Comprehensive Review on Photobiomodulation - https://www.mdpi.com/1422-0067/25/8/4483
14 Assessing Ultraviolet and Infrared Radiation Penetration Through Clothing - https://scholarworks.boisestate.edu/commhealth_facpubs/68/
15 Melatonin: Both a Messenger of Darkness and a Participant in the Cellular Actions of Non-Visible Solar Radiation of Near Infrared Light - https://pmc.ncbi.nlm.nih.gov/articles/PMC9855654/
16 Melatonin and the Optics of the Human Body - http://www.melatonin-research.net/index.php/MR/article/view/19
17 Longer wavelengths in sunlight pass through the human body and enhance mitochondrial function - https://www.nature.com/articles/s41598-025-09785-3
18 Mitochondria in skin health, aging, and disease - https://www.nature.com/articles/s41419-020-2649-z
19 Near-Infrared Light Exposure Triggers ROS to Downregulate Inflammatory Cytokines - https://www.mdpi.com/2076-3921/12/10/1824
20 Hamblin, M. R. (2017). Mechanisms and applications of the antiinflammatory effects of photobiomodulation. AIMS Biophysics, 4(3), 337–361. https://doi.org/10.3934/biophy.2017.3.337
21 Liao, W.T., Hung, C.H., Liang, S.S., Yu, S., Lu, J.H., Lee, C.H., Chai, C.Y., & Yu, H.S. (2021). Antiinflammatory effects induced by nearinfrared light irradiation through M2 macrophage polarization. Journal of Investigative Dermatology, 141(8), 2056–2066.e10. https://doi.org/10.1016/j.jid.2020.11.035
22 Webb AR, et al. (2024). Globally Estimated UVB Exposure Times Required to Maintain Sufficiency in Vitamin D Levels. https://pmc.ncbi.nlm.nih.gov/articles/PMC11124381/
23 Samanek AJ, et al. (2006). Estimates of beneficial and harmful sun exposure times during the year for major Australian population centres. https://www.mja.com.au/journal/2006/184/7/estimates-beneficial-and-harmful-sun-exposure-times-during-year-major-australian
24 Al-Dujaili MJS, et al. (2024). Investigating the Optimal Duration of the Sun Exposure for Adequate Cutaneous Synthesis of Vitamin D3 in Baghdad City: Depending on Fitzpatrick Skin Classification for Different Skin Types. https://www.researchgate.net/publication/377818875_Investigating_the_Optimal_Duration_of_the_Sun_Exposure_for_Adequate_Cutaneous_Synthesis_of_Vitamin_D3_in_Baghdad_City_Depending_on_Fitzpatrick_Skin_Classification_for_Different_Skin_Types
25 Chalcraft JR, et al. (2020). Vitamin D Synthesis Following a Single Bout of Sun Exposure in Older and Younger Men and Women. https://www.mdpi.com/2072-6643/12/8/2237
26 Terushkin V, et al. (2010). Estimated equivalency of vitamin D production from natural sun exposure versus oral vitamin D supplementation across seasons at two US latitudes. https://www.sciencedirect.com/science/article/abs/pii/S0190962209009487
27 Bogh MKB, et al. (2010). Vitamin D Production after UVB Exposure Depends on Baseline Vitamin D and Total Cholesterol but Not on Skin Pigmentation. https://www.sciencedirect.com/science/article/pii/S0022202X15347035
28 Alfredsson L, et al. (2020). Insufficient Sun Exposure Has Become a Real Public Health Problem. https://pmc.ncbi.nlm.nih.gov/articles/PMC10239563/
29 Engelsen O. (2010). The Relationship between Ultraviolet Radiation Exposure and Vitamin D Status. https://www.tandfonline.com/doi/full/10.3109/00365513.2012.681929
30 Webb AR, Engelsen O. (2006). Calculated Ultraviolet Exposure Levels for a Healthy Vitamin D Status. https://academic.oup.com/jbmrplus/article/5/1/e10460/7486276
31 Estimation of exposure durations for vitamin D production and erythema risk in the nose for urban environments in Bolivia and Germany. https://pubmed.ncbi.nlm.nih.gov/30992519/
32 Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers, and cardiovascular disease. https://pubmed.ncbi.nlm.nih.gov/15585788/
33 Estimated equivalency of vitamin D production from natural sun exposure versus oral vitamin D supplementation across seasons at two US latitudes. https://pubmed.ncbi.nlm.nih.gov/20363523/
34 Reassessing Impacts of Extended Daily Exposure to Low Level Solar UV Radiation of Human Skin. McKenzie RL, Liley JB. Photochemistry and Photobiology. 2018;94(6):1215-1220. https://pubmed.ncbi.nlm.nih.gov/30218096/
35 Health risks of extended exposure to low-level UV radiation – An analysis of ground-based and satellite-derived data. Guzikowski J, Krzyścin JW. Science of The Total Environment. 2022;831:154829. https://www.sciencedirect.com/science/article/abs/pii/S0048969722019921
36 Review of the Global Solar UV Index 2015 Workshop Report. Lehmann B, Pfahlberg A, Sandmann H, et al. Health Physics. 2018;114(1):84-90. https://pubmed.ncbi.nlm.nih.gov/30085971/
37 Vitamin D Stored in Fat Tissue During a 5-Year Intervention Affects Serum 25-Hydroxyvitamin D Levels in Finnish Men. https://academic.oup.com/jcem/article/102/10/3731/4036364
38 Efficacy of intermittent versus daily vitamin D supplementation on improving circulating 25(OH)D concentration: a Bayesian network meta-analysis of randomized controlled trials. https://pmc.ncbi.nlm.nih.gov/articles/PMC10488712/
39 Vitamin D oral intermittent treatment (DO IT) study, a randomized clinical trial. https://www.nature.com/articles/s41598-021-97417-x
40 Estimation of exposure durations for vitamin D production and erythema risk in the nose for urban environments in Bolivia and Germany. https://pubmed.ncbi.nlm.nih.gov/30992519/
41 Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers, and cardiovascular disease. https://pubmed.ncbi.nlm.nih.gov/15585788/
42 Estimated equivalency of vitamin D production from natural sun exposure versus oral vitamin D supplementation across seasons at two US latitudes. https://pubmed.ncbi.nlm.nih.gov/20363523/
43 The role of glass as a barrier against the transmission of ultraviolet radiation: an experimental study. https://pubmed.ncbi.nlm.nih.gov/19614895/
44 Use of UV-protective windows and window films to aid in the prevention of skin cancer. https://pubmed.ncbi.nlm.nih.gov/15479155/
45 Does Sunlight Through Glass Provide Vitamin D? https://www.nytimes.com/2019/02/08/well/live/does-sunlight-through-glass-provide-vitamin-d.html
46 The effect of sunscreen on vitamin D: a review. https://pubmed.ncbi.nlm.nih.gov/30945275/
47 Sunscreen and 25-Hydroxyvitamin D Levels: Friends or Foes? A Systematic Review and Meta-Analysis. https://pubmed.ncbi.nlm.nih.gov/40246233/
48 Sunscreens suppress cutaneous vitamin D3 synthesis. https://pubmed.ncbi.nlm.nih.gov/3033008/
49 Sunscreens block cutaneous vitamin D production with little impact on circulating 25-hydroxyvitamin D. https://pubmed.ncbi.nlm.nih.gov/28718005/
50 Sunlight and Skin Type as Drivers of Vitamin D Deficiency at UK Latitudes. https://pubmed.ncbi.nlm.nih.gov/29642423/
51 Skin color is relevant to vitamin D synthesis. https://pubmed.ncbi.nlm.nih.gov/24134867/
52 Assessment of the feasibility of using sunlight exposure to obtain the recommended level of vitamin D for UK dwelling adults of South Asian ethnic origin. https://pubmed.ncbi.nlm.nih.gov/26442223/
53 The Effect of Sunlight Exposure on Vitamin D Status in Countries of Low and High Latitudes: A Systematic Narrative Review. https://pubmed.ncbi.nlm.nih.gov/36522570/
54 Fractional Sunburn Threshold UVR Doses Generate Equivalent Vitamin D and DNA Damage in Skin Types I-VI but with Epidermal DNA Damage Gradient Correlated to Skin Darkness. https://pubmed.ncbi.nlm.nih.gov/29730334/
55 Endler, J. A. (1993). The Color of Light in Forests and Its Implications. Ecological Monographs, 63(1), 1–27. https://esajournals.onlinelibrary.wiley.com/doi/10.2307/2937121
56 Esch, T., et al. (2023). Effects of Near-Infrared Light on Well-Being and Health in Human Subjects with Mild Sleep-Related Complaints: A Double-Blind, Randomized, Placebo-Controlled Study. Biology, 12(1), 60. https://pmc.ncbi.nlm.nih.gov/articles/PMC9855677/
57 Zago, R. R., et al. (2020). Sunlight and health: shifting the focus from vitamin D3 to photobiomodulation by red and near-infrared light. Ageing Research Reviews, 61, 101089. https://www.sciencedirect.com/science/article/abs/pii/S1568163720302245
58 Lee, S. Y., et al. (1996). Light spectral composition in a tropical forest: measurements and model. Tree Physiology, 16(1-2), 69-79. https://academic.oup.com/treephys/article/16/1-2/69/1651960
59 Hamblin, M. R. (2016). Shining light on the head: Photobiomodulation for brain disorders. BBA Clinical, 6, 113-124. https://pmc.ncbi.nlm.nih.gov/articles/PMC5066074/ (General NIR benefits, extendable to natural exposure)
60 Melatonin and the Optics of the Human Body - http://www.melatonin-research.net/index.php/MR/article/view/19
61 Vitamin D Status of the British African-Caribbean Residents: Seasonal Variation and Determinants (2021): https://pubmed.ncbi.nlm.nih.gov/34836358/
62 Increased vitamin D intake differentiated according to skin color is needed to maintain 25-hydroxyvitamin D sufficiency across the winter: a randomized controlled trial in young Caucasian and African American women (2017): https://pubmed.ncbi.nlm.nih.gov/28615261/
63 Vitamin D insufficiency in a multiethnic cohort of breast cancer survivors (2019): https://pubmed.ncbi.nlm.nih.gov/31680267/
64 Avoidance of vitamin D deficiency to slow the COVID-19 pandemic (2020): https://pubmed.ncbi.nlm.nih.gov/33230496/
65 A review of smartphone applications for promoting sun protection practices (2018). https://www.jaad.org/article/S0190-9622(18)32953-0/fulltext
66 Comparison between EPA UV index app and UV monitor to assess risk for solar ultraviolet radiation exposure in agricultural settings in Eastern North Carolina (2020). https://pubmed.ncbi.nlm.nih.gov/33284740/
67 Smartphone mobile application delivering personalized, real-time sun protection advice: a randomized controlled clinical trial (2015). https://pubmed.ncbi.nlm.nih.gov/25629710/
68 The Effects of Using the Sun Safe App on Sun Health Knowledge and Behaviors of Young Teenagers: Results of Pilot Intervention Studies (2022). https://pmc.ncbi.nlm.nih.gov/articles/PMC10334904/
69 Use of smartphone apps to monitor human exposure to solar radiation: Comparison between predicted and measured UV index values (2020). https://www.sciencedirect.com/science/article/abs/pii/S0013935120301675