The practice of “heliotherapy” or the use of light (generally sunlight) to produce health benefits dates back as far as Hippocrates, who is said to have recommended sunlight exposure for medical purposes. Since this time it has been established that wavelengths of light contained in sunshine can have notable effects on human health. Ultraviolet light stimulates the production of vitamin D in the skin. Visible light (especially blue light), when it reaches the eyes, suppresses the synthesis of the hormone melatonin. Finally, infrared light also appears to have notable biological effects which will be discussed later.
A number of studies have observed an apparent relationship between factors affecting sun exposure in populations and coronary heart disease mortality. For example, a given area is exposed to more sunlight the closer the it is to the equator, so latitude is a variable which can affect a population’s level of sunshine exposure. A number of ecological studies have reported an increase in coronary heart disease mortality in populations as latitude increases1-6.
Season changes the amount of sunlight an area’s population is exposed to throughout the year, with summer representing the period of greatest sunlight and winter the period of least sunlight. A number of studies on populations throughout the world (in both the northern and southern hemispheres) have reported coronary heart disease mortality is higher in the winter than the summer7-15.
Altitude can also affects sunlight exposure, as sunlight intensity is greater at higher altitudes. It has been frequently observed that people living at higher altitudes have a lower mortality from coronary heart disease16-20.
A limited number of studies have examined actual levels of sunlight on rates of coronary heart disease. These studies, performed in the United Kingdom, have observed a reduction in coronary heart disease risk with greater sunlight exposure21-23.
Finally, serum levels vitamin D, an indirect marker of sunlight exposure, have frequently been associated with a lower risk of coronary heart disease mortality24-28. Understandably, this has resulted in many proposing that sunlight exposure may protect against coronary heart disease mortality due to its ability to stimulate vitamin D production. Further support for this hypothesis comes from randomized experiments where vitamin D supplementation seems to reduce risk factors for atherosclerosis and cardiovascular disease, such as blood pressure32 and inflammation markers29-31. However, long term clinical trials on vitamin D supplementation have provided almost no support for the hypothesis that vitamin D protects against coronary heart disease33,34
Furthermore, genetic evidence64 (which helps minimize confounding) looking at variations in the enzymes which activate vitamin D (increasing active vitamin D levels in the body) show no effect of lower vitamin D on cardiovascular disease risk:
In 1996 a paper entitled “Sunlight and Heart Disease”, published in the Quarterly Journal of Medicine investigated the relationship between sunlight exposure and coronary heart disease mortality rates5. Similar to other studies a reduction in death from coronary heart disease with greater sunlight exposure was observed (in the United Kingdom specifically). The investigators also observed that cholesterol levels varied both by season and by latitude, both suggesting greater sunlight exposure lowers cholesterol levels (see graph below). This is not the only time such observation has been made; a number of studies have reported that cholesterol levels are higher in the winter35 and at higher latitudes36.
There is little experimental evidence on sunlight and cholesterol levels, although one trial performed in Russia in 1966 reported that sunbathing reduced cholesterol levels in patients with coronary atherosclerosis37. A trial on psoriasis patients in Norway reported a 7% reduction in LDL cholesterol’s after 15 days of treatment, but this effect did not quite reach statistical significance (p=0.074)38.
Because LDL cholesterol (i.e. its oxidation in the sub-endothelial space) appears to be involved in atherosclerosis39, the ability of sunlight to reduce LDL could represent a potential mechanism involved in the seemingly protective role of sunlight on CHD.
The authors of “Sunlight and Heart Disease” speculated that cholesterol levels may be lowered by sunlight due to the action of vitamin D or the process of it’s synthesis. However, randomized clinical trials have reported quite consistently that oral vitamin D supplementation does not lower LDL cholesterol levels40,41. Furthermore, studies appear to show exposure to ultraviolet light alone also does not lower cholesterol either42-46. Thus, it would seem another explanation must be required to explain the potentially hypocholesterolemic effect of sunlight. One potential candidate for the effect may infrared light.
Infrared light appears have some significant biological effects. Perhaps most notably, it appears to stimulate mitochondrial enzymes46,48 and in doing so, increase levels of ATP47,48, the main energy unit of the cell. Experiments in which human50-53 or animal subjects54 are exposed to infrared light have generally reported a reduction in cholesterol levels. Furthermore, infrared light also appears to reduce inflammation55-59. In one experiment the inflammation markers TNF-a and IL-6 were dramatically lower after exposure to infrared light59. Because inflammation appears to play role in coronary heart disease60-62 this represents another mechanism by which infrared light (from sunlight) may protect against CHD. Finally, an experiment on rabbits found a reduction in atherosclerosis from infrared light exposure54.
However, it should not be concluded that infrared light represents the only component of sunlight which can help prevent CHD. Ultraviolet light may have cardioprotective effects independently of vitamin D (i.e. UV light increases nitric oxide signaling63). It is also feasible that the effect of visible light in sunshine on melatonin secretion and circadian rhythm regulation could also exert effects on CHD risk. Therefore, the ultimate contribution of infrared light to the seemingly protective role of sun exposure, while seemingly important, remains unclear.
1. Zittermann, A., Schleithoff, S.S., Koerfer, R., 2005. Putting cardiovascular disease and vitamin D insufficiency into perspective. Br. J.Nutr. 94, 483–492.
2. Fabsitz R, Feinleib M. Geographic patterns in county mortality rates from cardiovascular diseases. Am J Epidemiol. 1980 Mar;111(3):315-28.
3. Gardner, M J Patterns of mortality in middle and early old age in the county boroughs of England and Wales.Br J Prev Soc Med 1969;23:133-140
4. McGlashan ND. Spatial variations in cause-specific mortality in Australia, p. 1—28 from Studies in Australian Mortality. Ed. ND McGlaihan. En-vironmental Studies Occasional Paper University of Tasmania.
5. Grimes DS, Hindle E, Dyer T. Sunlight, cholesterol and coronary heart disease. QJM. 1996 Aug;89(8):579-89
6. Sinclair H. Latitude and ischaemic heart disease. Lancet. 1989 Apr22;1(8643):895
7. Mehta RH, Manfredini R, Bossone E, Fattori R, Evagelista A, Boari B, Cooper JV, Sechtem U, Isselbacher EM, Nienaber CA, Eagle KA; International Registry of Acute Aortic Dissection (IRAD) Investigators. The winter peak in the occurrence of acute aortic dissection is independent of climate. Chronobiol Int. 2005;22(4):723-9
8. Eurowinter Group. Cold exposure and winter mortality from ischaemic heart disease, cerebrovascular disease, respiratory disease, and all causes in warm and cold regions of Europe. Lancet 1997; 349: 1341–1346.
9. Douglas AS, Allan TM, Rawles JM. Composition of seasonality of disease. Scot Med J 1991; 36: 76–82.3.
10. Douglas AS, Russell D, Allan TM. Seasonal, regional and secular variations of cardiovascular and cerebrovascular mortality in New Zealand. Aust NZ J Med 1990; 20: 669–676
11. Seto TB, Mittleman MA, Davis RB, Taira DA, Kawachi I. Seasonal variation in coronary artery disease mortality in Hawaii: observational study. BMJ. 1998 Jun 27;316(7149):1946-7
12. Marshall RJ, Scragg R, Bourke P. An analysis of the seasonal variation of coronary heart disease and respiratory disease mortality in New Zealand. Int J Epidemiol. 1988 Jun;17(2):325-31
13. Kloner RA, Poole WK, Perritt RL. When throughout the year is coronary death most likely to occur? A 12-year population-based analysis of more than 220 000 cases. Circulation. 1999 Oct 12;100(15):1630-4
14. Weerasinghe DP, MacIntyre CR, Rubin GL. Seasonality of coronary artery deaths in New South Wales, Australia. Heart. 2002 Jul;88(1):30-4
15.Pell JP, Cobbe SM. Seasonal variations in coronary heart disease. QJM. 1999Dec;92(12):689-96. Review
16. Faeh D, Gutzwiller F, Bopp M; Swiss National Cohort Study Group. Lower mortality from coronary heart disease and stroke at higher altitudes in Switzerland. Circulation. 2009 Aug 11;120(6):495-501
17. Ezzati M, Horwitz ME, Thomas DS, Friedman AB, Roach R, Clark T, Murray CJ,Honigman B. Altitude, life expectancy and mortality from ischaemic heart disease,stroke, COPD and cancers: national population-based analysis of US counties. JEpidemiol Community Health. 2012 Jul;66(7):e17.
18. Voors AW, Johnson WD. Altitude and arteriosclerotic heart disease mortality in white residents of 99 of the 100 largest cities in the United States. J ChronicDis. 1979;32(1-2):157-62
19. Mortimer EA Jr, Monson RR, MacMahon B. Reduction in mortality from coronary heart disease in men residing at high altitude. N Engl J Med 1977 Mar 17;296(11):581-585.
20. Weinberg CR, Brown KG, Hoel DG Altitude, radiation, and mortality from cancer and heart disease. Radiat Res 1987 Nov;112(2):381-390.
21. MacPherson A, Bacsó J. Relationship of hair calcium concentration to incidence of coronary heart disease. Sci Total Environ. 2000 Jun 8;255(1-3):11-9
22. Morris RW, Whincup PH, Lampe FC, Walker M, Wannamethee SG, Shaper AG. Geographic variation in incidence of coronary heart disease in Britain: the contribution of established risk factors. Heart. 2001 Sep;86(3):277-83
23. Prospective study where average daily sunshine correlated with lower CHD mortality, but not when adjusted for things including cholesterol
24. Holick MF. Vitamin D deficiency. N Engl J Med. 2007 Jul 19;357(3):266-81. Review
25. Wang L, Song Y, Manson JE, Pilz S, März W, Michaëlsson K, Lundqvist A, Jassal SK, Barrett-Connor E, Zhang C, Eaton CB, May HT, Anderson JL, Sesso HD.Circulating 25-hydroxy-vitamin D and risk of cardiovascular disease: a meta-analysis of prospective studies. Circ Cardiovasc Qual Outcomes. 2012Nov;5(6):819-29
26. Ginde AA, Scragg R, Schwartz RS, Camargo CA Jr. Prospective study of serum25-hydroxyvitamin D level, cardiovascular disease mortality, and all-cause mortality in older U.S. adults. J Am Geriatr Soc. 2009 Sep;57(9):1595-603
27. Ginde AA, Scragg R, Schwartz RS, Camargo CA Jr. Prospective study of serum 25-hydroxyvitamin D level, cardiovascular disease mortality, and all-cause mortality in older U.S. adults. J Am Geriatr Soc. 2009 Sep;57(9):1595-603
28. Lee JH, O’Keefe JH, Bell D, Hensrud DD, Holick MF. Vitamin D deficiency an important, common, and easily treatable cardiovascular risk factor? J Am Coll Cardiol. 2008 Dec 9;52(24):1949-56
29. Schleithoff SS, Zittermann A, Tenderich G, Berthold HK, Stehle P, Koerfer R.Vitamin D supplementation improves cytokine profiles in patients with congestive heart failure: a double-blind, randomized, placebo-controlled trial. Am J Clin Nutr. 2006 Apr;83(4):754-9
30. Zittermann, A., Schleithoff, S.S., Koerfer, R., 2005. Putting cardiovascular disease and vitamin D insufficiency into perspective. Br. J.Nutr. 94, 483–492.
31. Zittermann A, Frisch S, Berthold HK, Götting C, Kuhn J, Kleesiek K, Stehle P, Koertke H, Koerfer R. Vitamin D supplementation enhances the beneficial effects of weight loss on cardiovascular disease risk markers. Am J Clin Nutr. 2009 May;89(5):1321-7
32. Witham MD, Nadir MA, Struthers AD. Effect of vitamin D on blood pressure: a systematic review and meta-analysis. J Hypertens. 2009 Oct;27(10):1948-54
33. Ford JA, MacLennan GS, Avenell A, Bolland M, Grey A, Witham M; RECORD Trial Group. Cardiovascular disease and vitamin D supplementation: trial analysis,systematic review, and meta-analysis. Am J Clin Nutr. 2014 Sep;100(3):746-55
34. Wang L, Manson JE, Song Y, Sesso HD. Systematic review: Vitamin D and calcium supplementation in prevention of cardiovascular events. Ann Intern Med. 2010 Mar 2;152(5):315-23
35. Gordon DJ, Hyde J, Trost DC, Whaley FS, Hannan PJ, Jacobs DR, Ekelund LG. Cyclic seasonal variation in plasma lipid and lipoprotein levels: the Lipid Research Clinics Coronary Primary Prevention Trial Placebo Group. J Clin Epidemiol. 1988;41(7):679-89
36. Verschuren WM, Jacobs DR, Bloemberg BP, Kromhout D, Menotti A, Aravanis C, Blackburn H, Buzina R, Dontas AS, Fidanza F, et al. Serum total cholesterol and long-term coronary heart disease mortality in different cultures. Twenty-five-year follow-up of the seven countries study. JAMA. 1995 Jul 12;274(2):131-6
37. Mikhailov VA. “Influence of graduated sunlight baths on patients with coronary atherosclerosis.” Sovet Med 1966
38. Osmancevic A, Nilsen LT, Landin-Wilhelmsen K, Søyland E, Abusdal Torjesen P,Hagve TA, Nenseter MS, Krogstad AL. Effect of climate therapy at Gran Canaria on vitamin D production, blood glucose and lipids in patients with psoriasis. J Eur Acad Dermatol Venereol. 2009 Oct;23(10):1133-40
39. Steinberg D, The Cholesterol Wars: The Skeptics vs. The Preponderance of the Evidence. 2000; San Diego: Academic Press
40. Zittermann A, Frisch S, Berthold HK, Götting C, Kuhn J, Kleesiek K, Stehle P, Koertke H, Koerfer R. Vitamin D supplementation enhances the beneficial effects of weight loss on cardiovascular disease risk markers. Am J Clin Nutr. 2009 May;89(5):1321-7. UV light increases vitamin D but doesn’t lower LDL
41. Wang H, Xia N, Yang Y, Peng DQ. Influence of vitamin D supplementation onplasma lipid profiles: a meta-analysis of randomized controlled trials. LipidsHealth Dis. 2012 Mar 20;11:42
42. Romani J, Caixas A, Carrascosa JM, Ribera M, Rigla M, and Luelmo J. Effect of narrowband ultraviolet B therapy on inflammatory markers and body fat composition in moderate to severe psoriasis. Br J Dermatol 2012;166(6):1237-44.
43. Coimbra S, Oliveira H, Reis F, Belo L, Rocha S, Quintanilha A, Figueiredo A,Teixeira F, Castro E, Rocha-Pereira P, Santos-Silva A. Psoriasis therapy and cardiovascular risk factors: a 12-week follow-up study. Am J Clin Dermatol. 2010 Dec 1;11(6):423-32
44. Black HS, Henderson SV, Kleinhans CM, Phelps AW, Thornby JI. Effects of dietary cholesterol on ultraviolet light carcinogenesis. Cancer Res. 1979 Dec;39(12):5022-7
45. ARİF ALTINAŞ, ALİ BİLGİLİ, DİNÇ EŞSİZ, NİLGÜN ÜREN, LEVENT ALTINTAŞ, MERT PEKCAN, HÜSEYİN TÜRKER, AND ÇAKIR SERKAN EFFECTS OF ARTIFICIAL ULTRAVIOLET C RADIATION ON SEVERAL BLOOD AND URINE PARAMETERS RELATED TO RENAL AND HEPATIC FUNCTIONS IN ALBINO MICE Bull Vet Inst Pulawy 51, 303-308, 2007
46. Barth J, Kohl V, Hanefeld M. [Behavior of lipids, other serum parameters and cardiovascular functions in ultraviolet therapy]. Hautarzt. 1994 Oct;45(10):702-7. German
47. Ann Biomed Eng. 2012 Feb;40(2):516-33. The nuts and bolts of low-level laser (light) therapy. Chung H, Dai T, Sharma SK, Huang YY, Carroll JD, Hamblin MR.
48. IUBMB Life. 2010 Aug;62(8):607-10. Multiple roles of cytochrome c oxidase in mammalian cells under action of red and IR-A radiation. Karu TI.
49. Brain Res. 2010 Jan 8;1306:100-5. Transcranial near infrared laser treatment (NILT) increases cortical adenosine-5′-triphosphate (ATP) content following embolic strokes in rabbits. Lapchak PA, De Taboada L.
50. Jackson et al: Reduction in Cholesterol and Triglyceride Serum Levels Following Low-Level Laser Irradiation: A Noncontrolled, Nonrandomized Pilot Study (2010)
51. Maloney et al: The reduction in cholesterol and triglyceride serum levels following low-level laser irradiation: a non-controlled, non-randomized pilot study (2009
52. Ambulatory Application of Combined Laser Therapy in Patients with Diabetes Mellitus and Dyslipidemia. Laser Partner, 17.5.2002 T.V. Kovalyova
53. T V Kovalyova, A V Farvayeva, L T Pimenov, S M Denisov, “Dynamics of hyperlipidemia and peripheral blood flow in patients with diabetes mellitus after the course of combined laser therapy in ambulatory polyclinic conditions”, Medical Academy, 2nd Municipal Out-Patient Department, Izhevsk, RF Russian Medical University, 13th State Clinic Hospital, Moscow, RF.
54. Lab Anim Res. 2012 Mar;28(1):39-46. Anti-hypercholesterolemic and anti-atherosclerotic effects of polarized-light therapy in rabbits fed a high-cholesterol diet. Park D, Kyung J, Kim D, Hwang SY, Choi EK, Kim YB.
55. Dose Response. 2009 Sep 1;7(4):358-83. Biphasic dose response in low level light therapy. Huang YY, Chen AC, Carroll JD, Hamblin MR.
56. Oral Pathol Med. 2015 Feb;44(2):94-102. Anti-inflammatory effect of 635 nm irradiations on in vitro direct/indirect irradiation model. Lim W, Choi H, Kim J, Kim S, Jeon S, Zheng H, Kim D, Ko Y, Kim D, Sohn H, Kim O.
57. Arthritis Res Ther. 2013;15(5):R116. Effect of low-level laser therapy on the expression of inflammatory mediators and on neutrophils and macrophages in acute joint inflammation. Alves AC, Vieira R, Leal-Junior E, dos Santos S, Ligeiro AP, Albertini R, Junior J, de Carvalho P.
58. Lasers Med Sci. 2013 May;28(3):1007-16. Low-level laser therapy improves the inflammatory profile of rats with heart failure. Hentschke VS, Jaenisch RB, Schmeing LA, Cavinato PR, Xavier LL, Dal Lago P.
59. Photomed Laser Surg. 2006 Apr;24(2):129-39. Pro- and anti-inflammatory cytokine content in human peripheral blood after its transcutaneous (in vivo) and direct (in vitro) irradiation with polychromatic visible and infrared light. Zhevago NA, Samoilova KA.
60. Zakynthinos E, Pappa N. Inflammatory biomarkers in coronary artery disease. J Cardiol. 2009 Jun;53(3):317-33. doi: 10.1016/j.jjcc.2008.12.007. Epub 2009 Jan 29. Review
61. Libby P. Inflammation and cardiovascular disease mechanisms. Am J Clin Nutr. 2006 Feb;83(2):456S-460S. Review
62. Ridker PM, Morrow DA. C-reactive protein, inflammation, and coronary risk. Cardiol Clin. 2003 Aug;21(3):315-25. Review
63. Feelisch M, Kolb-Bachofen V, Liu D, Lundberg JO, Revelo LP, Suschek CV, Weller RB. Is sunlight good for our heart? Eur Heart J. 2010 May;31(9):1041-5. doi: 10.1093/eurheartj/ehq069. Epub 2010 Mar 9
64. Manousaki D, Mokry LE, Ross S, Goltzman D, Richards JB. Mendelian Randomization Studies Do Not Support a Role for Vitamin D in Coronary Artery Disease. Circ Cardiovasc Genet. 2016 Aug;9(4):349-56. doi: 10.1161/CIRCGENETICS.116.001396. Epub 2016 Jul 14