Photobiomodulation Science

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PBM Database literature map

Sunlight research

Studies examine time outdoors, daylight, solar UVA or UVB, and sunlight as a whole. The literature includes population studies and reviews, laboratory research, and a smaller number of human daylight interventions.

Sunlight and healthSunlight has several biological pathways. Ultraviolet radiation can stimulate vitamin D synthesis but also cause DNA damage, skin cancer and eye damage. Research covers several health areas; the overall effect depends on exposure and individual susceptibility. SUNLIGHT EYES Visible daylight Circadian timing Melatonin regulation Mood & alertness ULTRAVIOLET UVA & UVB Physiological responses Vitamin D synthesis Nitric oxide release Immune modulation UV-related harms Sunburn / DNA damage Skin ageing / skin cancer Eye damage BLUE LIGHT Local skin effects Nitric oxide release Endorphin production Cellular responses Pigmentation · melasma aggravation RED / NIR Photobiomodulation Mitochondrial function ATP production Inflammation modulation Tissue repair FAR-INFRARED Thermal effects Vascular function Microcirculation HEALTH AREAS STUDIED Brain & daily rhythm Sleep & circadian rhythm Mood & depression Cognition & memory Heart & metabolism Blood pressure Cardiovascular disease Glucose & metabolism Immunity Multiple sclerosis Allergy & asthma Infections Cancer Breast & other cancers Skin cancer & melanoma Cancer survival Body & lifespan Bone health & balance Frailty Mortality Eyes & skin Myopia & presbyopia Atopic dermatitis Skin structure BENEFITS & HARMS Potential benefits UV-related harms · high exposure Circadian regulation · vitamin D PBM: energy metabolism and tissue repair Inflammation modulation Local and systemic responses Sunburn · DNA damage Skin ageing Skin cancer risk Eye damage Overall health effect Benefit–harm balance is one factor; exposure and skin type influence it.
Health topics are studied associations. PBM and far-infrared mechanisms draw largely on device research; their contribution to sunlight’s health effects remains uncertain. Sources: Heiskanen et al. (2020) · WHO: UV health effects.

Visual evidence overview

Sunlight and health: what studies report

Selected findings on disease risk, wellbeing and daylight interventions. Most are observational associations; studies measure different exposures, from time outdoors to ambient UV and window daylight.

Updated

All-cause mortality

Inverse associations, mixed overall

In a 20-year cohort of 29,518 Swedish women, those who avoided sun exposure had about twice the mortality rate of women reporting the highest exposure.1

A 2025 systematic review of 73 eligible articles found mixed mortality results across populations. Many studies used indirect exposure measures, and uncontrolled confounding limited interpretation.2

Blood pressure

Lower pressure with greater solar UV

An observational study followed 342,457 dialysis patients across 2,178 US centres for three years. Higher ambient UVA and UVB were associated with lower systolic blood pressure.

The association remained after adjustment for temperature and patient characteristics. Solar exposure was estimated for clinic locations, so the analysis did not measure each patient’s time in sunlight.3

Cardiovascular disease

Seasonal patterns in heart attacks

A Scottish time-series analysis examined 56,370 myocardial infarctions between 2000 and 2011. Heart attacks showed a seasonal pattern, with more events in winter and fewer in summer.

Higher ambient UVA was associated with fewer events after accounting for temperature and UVB. The analysis compared regional and seasonal conditions, rather than individual sun exposure.4

Multiple sclerosis

Lower sun exposure, higher MS risk

Two Swedish case–control studies compared 7,069 people with multiple sclerosis with 6,632 controls. Lower sun exposure was associated with higher MS risk.

Mediation analysis attributed nearly 30% of the association to vitamin D deficiency. A separate association remained, suggesting that vitamin D may explain only part of the relationship with sunlight.5

Type 2 diabetes

A gradient across exposure habits

In an 11-year follow-up of a Swedish women’s cohort, 24,098 participants provided follow-up information. Those reporting moderate or low sun exposure had higher odds of type 2 diabetes.

Compared with the highest-exposure group, the odds ratios were 1.47 and 2.47, respectively. The association remained after adjustment for age, exercise, education and other measured factors.6

Glucose control

A small trial of window daylight

A randomized crossover trial compared natural window daylight with constant artificial lighting in 13 people with type 2 diabetes. Each lighting condition lasted 4.5 days during office hours.

Continuous glucose monitoring showed more time in the normal glucose range under daylight. Metabolic measurements also indicated greater reliance on fat oxidation during the daylight condition.7

Breast cancer

Lower incidence in pooled studies

A meta-analysis of 31 epidemiological studies linked higher sunlight exposure with lower breast cancer incidence (pooled odds ratio 0.80). Associations were stronger in case–control studies than in cohorts.

Results also varied by tumour subtype: inverse associations were reported for estrogen-receptor-negative and triple-negative disease, while no association was found for estrogen-receptor-positive breast cancer.8

Melanoma

Exposure pattern and skin sensitivity

Melanoma is associated with intermittent sun exposure, while findings for cumulative exposure are more complex. An Iowa population-based case–control study collected detailed lifetime exposure histories and measures of sun sensitivity.

High cumulative exposure was associated with higher melanoma odds among participants with medium or darker skin. Associations with total exposure early in life were minimal.9

Mood & depression

Cohort findings and a small trial

In UK Biobank, more daytime outdoor light was associated with fewer depressive symptoms and lower odds of major depression, after adjustment for demographic and lifestyle factors.10

A four-week randomized trial in 46 stroke survivors reported improved depression scores and daily functioning with sunlight exposure. Participants received at least 30 minutes daily on at least 14 days; cognition did not significantly improve.11

Sleep & body clock

Earlier timing, fewer sleep symptoms

UK Biobank analyses linked more time in daytime outdoor light with an earlier chronotype, easier morning waking, less tiredness and fewer insomnia symptoms. Exposure was reported as daily time outdoors.

Longitudinal analyses generally supported these patterns, although associations were smaller than in the cross-sectional comparisons. The study examined everyday light exposure rather than a prescribed daylight intervention.10

Dementia

A J-shaped association

A prospective cohort followed 362,094 adults for a median of nine years. Dementia risk showed a J-shaped association with reported outdoor light, with the lowest risk around 1.5 hours daily on average.

Risk was higher with both less and more exposure. The estimated minimum varied by season; these observational findings do not establish a preventive dose.12

Myopia

More outdoor time, less myopic refraction

A cross-sectional study in Pakistan examined 110 participants, mostly young people. More reported outdoor time in both summer and winter was associated with less myopic refraction.

Researchers combined exposure questionnaires with automated eye measurements. Because the study assessed participants at one point in time, it could not show whether more sunlight prevented myopia from developing.13

Allergy & asthma

Early-life solar radiation associations

The PARIS birth cohort assessed 1,080 children at age 8–9. Higher prenatal solar radiation was associated with less allergic sensitization and asthma; postnatal radiation was also associated with less sensitization.

Exposure estimates came from meteorological data. The overall comparison between high- and low-exposure trajectories narrowly missed statistical significance, although it was significant among children whose mothers received vitamin D supplements.14

Bone health

Sun exposure alongside physical activity

A 24-week intervention assigned 81 older adults with osteopenia to daytime walking, night-time walking, sun exposure or a control group. All groups received calcium.

Daytime walking produced the largest gains in lumbar bone density. Sun exposure alone and night-time walking also improved bone density, with no significant difference between them. Vitamin D levels were higher in the daytime-walking and sun-exposure groups.15

Crohn’s disease

Geographic differences in incidence

An ecological study compared Crohn’s disease incidence across 94 French regions using insurance records from 2000–2002. Regions with lower estimated sunlight had higher incidence.

No corresponding relationship was found for ulcerative colitis. The analysis, discussed in the 2020 sunlight review, used satellite-based regional exposure estimates rather than measurements of individual patients’ sunlight habits.16

Respiratory infections

Seasonal correlations with solar UV

An ecological analysis of US surveillance data found lower test positivity for four common coronaviruses in months with higher solar UV. It compared seasonal infection patterns with ambient radiation.

For SARS-CoV-2, inverse associations appeared in two US regions but were not significant elsewhere. These correlations could also reflect other seasonal changes in behaviour and environment.17

Based on the Sunlight study records and the epidemiological literature discussed in Heiskanen, Pfiffner & Partonen (2020). The review also explores red and near-infrared light as possible contributors to sunlight’s health effects; the associations above do not identify which wavelengths or mechanisms are responsible.

References for this overview
  1. Lindqvist PG et al. (2014). Avoidance of sun exposure is a risk factor for all-cause mortality: results from the Melanoma in Southern Sweden cohort.
  2. Parkhouse T et al. (2025). The effects of sunlight exposure on mortality: a systematic review of epidemiological studies.
  3. Weller RB et al. (2020). Does Incident Solar Ultraviolet Radiation Lower Blood Pressure?
  4. Mackay DF et al. (2019). UVA and Seasonal Patterning of 56 370 Myocardial Infarctions Across Scotland, 2000-2011.
  5. Hedström AK et al. (2020). Low sun exposure increases multiple sclerosis risk both directly and indirectly.
  6. Lindqvist PG et al. (2025). Sun Exposure and Type 2 Diabetes Mellitus: A Prospective Follow-up Cohort Study from Southern Sweden.
  7. Harmsen JF et al. (2026). Natural daylight during office hours improves glucose control and whole-body substrate metabolism.
  8. Petrelli F et al. (2026). Sunlight Exposure and Breast Cancer Risk: A Systematic Review and Meta-analysis.
  9. Dennis LK. (2022). Cumulative Sun Exposure and Melanoma in a Population-Based Case-Control Study: Does Sun Sensitivity Matter?
  10. Burns AC et al. (2021). Time spent in outdoor light is associated with mood, sleep, and circadian rhythm-related outcomes: A cross-sectional and longitudinal study in over 400,000 UK Biobank participants.
  11. Wang SJ et al. (2020). The effects of sunlight exposure therapy on the improvement of depression and quality of life in post-stroke patients: A RCT study.
  12. Ma LZ et al. (2022). Time spent in outdoor light is associated with the risk of dementia: a prospective cohort study of 362094 participants.
  13. Naqvi SAH et al. (2021). Sunlight Exposure: A Protective Role in the Development of Myopia.
  14. Lefebvre L et al. (2024). Early exposure to sunlight and allergic morbidity: The PARIS birth cohort.
  15. Cheng J et al. (2022). Effects of walking and sun exposure on bone density and balance in elderly with osteopenia.
  16. Nerich V et al. (2011). Low exposure to sunlight is a risk factor for Crohn's disease.
  17. Tang L et al. (2021). Sunlight ultraviolet radiation dose is negatively correlated with the percent positive of SARS-CoV-2 and four other common human coronaviruses in the U.S.

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182 records in the PBM Database · Primary studies and reviews

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Source: PBM Database, “Sunlight” category, accessed 4 October 2026. Categories are database labels; a record may appear under more than one study-design filter.

A bridge between sunlight and PBM

Red and near-infrared light in sunlight

Heiskanen, Pfiffner and Partonen (2020) reviewed how red and near-infrared light in sunlight could contribute to observed sunlight–health associations. The review connects epidemiological findings with photobiomodulation research, including effects on cellular energy metabolism, inflammation and tissue repair. It considers mitochondrial responses and findings across neurological, cardiovascular and metabolic conditions, drawing on both animal experiments and human studies.

The authors also discuss ultraviolet and blue light, possible systemic responses to irradiation, and how sunlight compares with the light sources used in PBM studies. They examine tissue penetration, light intensity and the broader skin exposure during outdoor activities, including near-infrared transmission through thin clothing. The article offers a framework for studying a possible link.

First page of Sunlight and health: shifting the focus from vitamin D3 to photobiomodulation by red and near-infrared light

Many disease-related findings come from observational research, which can identify associations but cannot by itself establish cause and effect. UV exposure, visible daylight and red or near-infrared light are different exposures and should not be treated as interchangeable.

Source: PBM Database, “Sunlight” category, checked 4 October 2026.