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Health benefits of sun exposure: vitamin D and beyond


Several recent papers have discussed whether the health benefits of solar UVB exposure are due to vitamin D production or other factors. [1],[2],[3],[4],[5],[6] This question has been raised since randomized controlled trials (RCTs) of vitamin D do not always support the findings from observational studies that report reduced risk of disease for those with higher vitamin D levels. This issue was famously proposed by Philippe Autier and colleagues in a 2014 paper, in which he suggested that “reverse causality”, i.e., the disease state could cause low vitamin D levels, could explain the findings from observational studies.

Autier hypothesized,

“The discrepancy between observational and intervention studies suggests that low 25(OH)D is a marker of ill health. Inflammatory processes involved in disease occurrence and clinical course would reduce 25(OH)D, which would explain why low vitamin D status is reported in a wide range of disorders.”[7]

In my opinion, there is little evidence to support that hypothesis. In fact, John Cannell, Michael Holick and I reviewed papers reporting changes in biomarkers of inflammation in vitamin D RCTs. We found that for those studies where the baseline vitamin D level was >20 ng/mL (50 nmol/L), there was only a 26% chance that a beneficial effect would be found. However, if the baseline level was <20 ng/mL, there was a 50% chance.[8] Thus, the discrepancies between observational studies and RCTs may simply be due to the fact that many vitamin D RCTs have been poorly designed, conducted and analyzed.

Additional evidence that “reverse causality” does not explain the discrepancy between observational studies related to vitamin D and RCTs was provided on January 17, 2017. An observational study of children who developed respiratory tract infections in Norway found inflammatory markers did not predict 25(OH)D status. Despite increased inflammation, vitamin D levels did not change during illness and after recovery.[9]

Researchers have found that high vitamin D levels are associated with lower risk of diseases, including multiple sclerosis, many types of cancer, cardiovascular disease (CVD) (congestive heart failure, coronary heart disease, stroke), dementia, dental caries, respiratory tract diseases, metabolic diseases, as well as adverse pregnancy and birth outcomes and all-cause mortality rates.[10] Let’s examine the evidence that vitamin D supplementation reduces risk of these health outcomes:

  • For cancer, RCTs have produced conflicting findings. These studies show the greatest benefits of vitamin D supplementation when they enroll patients with low baseline vitamin D levels (<20 ng/mL).[11],[12] However, there were also benefits in raising vitamin D levels from 30 to 40 ng/mL.[13],[14]
  • For CVD and metabolic diseases, most RCTs do not find beneficial effects of vitamin D supplementation, even when baseline vitamin D levels are low.[15] However, there does seem to be some benefit for congestive heart failure.
  • For dental caries, both UVB exposure and vitamin D supplementation, have shown to be protective.[16],[17]
  • For respiratory tract infections, RCTs have found beneficial effects of vitamin D3 for influenza and acute respiratory tract infections.[18],[19],[20],[21]
  • Vitamin D RCTs have found beneficial effects of vitamin D3 for pregnancy and birth outcomes, such as reduced risk of premature birth – when the results are analyzed with respect to vitamin D levels.[22]
  • RCTs have found a few percent reduction in all-cause mortality rate from vitamin D3 supplementation.[23]

In summary, there are some RCTs that have supported a role of vitamin D in reducing risk of various types of disease. In addition, mechanisms have generally been identified for how vitamin D plays a role in these health outcomes. However, there are three possible explanations for why some RCTs have been unable to prove a causal relationship between vitamin D supplementation and certain health outcomes:

  • The RCTs have not been conducted properly
  • The effects may be due to sun exposure through non-vitamin D mechanisms; in these cases, vitamin D level is an index of sun exposure.
  • There are other confounding factors responsible for the relationship between vitamin D status and the health outcome.

Beneficial effects of solar UV exposure

Geographical ecological studies treat populations defined geographically as units (e.g., states, countries) and look at health outcomes averaged for each population with respect to risk-modifying factors also averaged for each population. My recent review of such studies with respect to indices of solar UVB doses (e.g., latitude or UVB doses based on satellite instrument data) found that most of those that showed reduced rates for higher UVB doses were also supported by observational studies related to vitamin D.

My review concluded,

“Health outcomes discussed were based on the author’s knowledge and include anaphylaxis/food allergy, atopic dermatitis and eczema, attention deficit hyperactivity disorder, autism, back pain, cancer, dental caries, diabetes mellitus type 1, hypertension, inflammatory bowel disease, lupus, mononucleosis, multiple sclerosis, Parkinson disease, pneumonia, rheumatoid arthritis, and sepsis.”[24]

Here is a quick overview of findings related to UVB exposure for several diseases.

Multiple Sclerosis

For multiple sclerosis, mounting evidence indicates that both vitamin D and UVB exposure have independent effects on incidence and progression.[25],[26],[27]

Cardiovascular Disease

Incidence and mortality rates for CVD have large seasonal variations with higher rates in winter than in summer.[28] Several seasonal factors may explain the seasonal variation in CVD rates: UVB doses, vitamin D levels,[29] temperature and gene expression. Two recent papers reported that the expression of many types of genes vary seasonally, some highly expressed in winter, others in summer.[30],[31] Previous to these reports, a RCT found that vitamin D3 supplementation strongly affected the expression of many genes in white blood cells.[32] It is not clear what the effect of seasonal variation of gene expression is. Although, it was recently suggested that it plays a role in seasonal variations of death rates, especially for CVD.24

A recent paper reported that regular outdoor activities, independent of activity level, were associated with lower risk of CVD. The researchers also found that those with the highest frequency of outdoor activities and vitamin D level had the lowest risk of CVD and diabetes mellitus type II.[33] This finding may explain the link between sunshine and reduced risk of diabetes mellitus type 2 reviewed by Shore-Lorenti et al. [2014].[34]

Sun exposure protects against heart attacks even when vitamin D is not increased. Researchers analyzed the records of 628 first-time heart-attack patients and found that their chance of survival varied according to whether they were placed on the north (dark) side of the hospital or on the south (sunny) side—survival rate on the sunny side being about 25% better.[35]  It is unlikely that the positive relationship of sun to survival of heart disease patients was facilitated by vitamin D, since vitamin D-producing UVB is filtered out by window glass.[36] Nitric oxide, a vasodilator, is the likely photoproduct that provided the protection against heart attacks. The production of nitric oxide is stimulated by UVA, which is not filtered by window glass.

Recently, several papers have suggested that the non-vitamin D benefits of sun exposure are very important and may explain multiple of the effects attributed to vitamin D. The article by Hoel et al. starts by reviewing the risks of sun exposure, melanoma and nonmelanoma skin cancer.2 They point out that melanoma incidence rates in the U.S. have risen from 1 per 100,000 persons/yr in 1933 to 23 per 100,000 in 2012 and state that the reasons for this staggering rise are not well understood.

The review states,

“A plausible explanation for the rise in melanoma incidence since 1935 may be the continually-increasing insufficient non-burning sun exposure and related increasing vitamin D deficiency/insufficiency…”

The researchers then turn to the beneficial effects of solar UV exposure. Most of the health benefits appear to come from the production of vitamin D. These include reduced risk of bladder, breast, and colorectal cancer, but also that sun exposure reduces risk of non-Hodgkin’s lymphoma through some effect other than vitamin D.

My research indicates that UVB, through production of vitamin D, reduces the risk of about 15 types of cancer.[37] On the other hand, a mouse model study found that there were vitamin D-independent benefits of UVB exposure on colon cancer progression but not incidence.[38]

There are also benefits of sun exposure not linked to vitamin D. For example, UVA (320-400 nm) can liberate nitric oxide from nitrogen compounds under the skin, which can lower blood pressure.[39] Sunlight also affects the production of serotonin, and deficiencies in serotonin have been linked to multiple adverse consequences, including depression and Alzheimer’s disease. They also discuss a study reporting that children who spent less time in the sun had a greater risk of developing myopia (nearsightedness). The likely reason for this is that if the eyes do not have to focus on distant objects, they do not develop the capability to do so.

In their opinion, vitamin D supplementation is not an effective substitute for adequate sun exposure.

They conclude,

“The risks of inadequate non-burning sun exposure include increased risks of all-cause mortality, colorectal cancer, breast cancer, non-Hodgkins lymphoma, prostate cancer, pancreatic cancer, hypertension, cardiovascular disease, metabolic syndrome, type 2 diabetes, obesity, Alzheimer disease, multiple sclerosis, type 1 diabetes, rheumatoid arthritis, psoriasis, non-alcoholic fatty liver disease, statin intolerance, macular degeneration and myopia.”

It is time for the pendulum to swing back towards embracing the sun, rather than fearing it. The Vitamin D Council recommends safe, sensible sun exposure when an individual’s shadow is shorter than they are tall. It is important to note that one does not need to burn in order to receive adequate vitamin D from the sun.

Another recent paper examined the question: “Does sunlight protect us from cancer?”.[40] Certainly it does, especially through production of vitamin D. They suggested several ways this could happen, including induction of anti-inflammatory cytokines, activation of regulatory cells, lowering blood pressure through release of nitric oxide, folate degradation and effect of endorphins on the neuroimmune system. While these mechanisms may play a role, much more work is required to determine whether and/or how much these mechanisms may be.

The roles of UV exposure and vitamin D on the seasonality and outcomes of infectious diseases were reviewed in a recent paper.[41] In this paper, which included 279 references, they discussed the evidence for the effects of both UV exposure and vitamin D including findings from population and animal studies and the mechanisms that have been identified.

The researchers concluded,

“Due to the many seasonal covariates (melatonin, temperature, humidity, favourable transmission dynamics, social behaviour changes), there are many other factors which could lead to, and more likely compound, the seasonality of infectious disease prevalence that is associated with seasonal vitamin D deficiency at high latitudes. Nevertheless, it is clear that (1) UVR has both vitamin D-dependent and independent effects on infectious diseases, (2) that these effects vary depending on the pathogen of interest and (3) that the effects can be cumulative, complementary or antagonistic.”

Benefits of safe UV exposure

There is widespread concern about the risk of skin cancer and melanoma from solar UV exposure. This concern is way overblown. First, the health benefits of UV exposure greatly outweigh the adverse effects of solar UV exposure.[42] Second, those who are occupationally exposed to sunlight do not have an increased risk of melanoma.[43],[44] The reasons may include that the body has many ways to protect against melanoma such as tanning, thickening of the outer layer of the skin and vitamin D production. Third, wearing sunscreen when there is no danger of sunburning actually increases risk of melanoma.[45] The important things regarding solar UV exposure are that it should be regular so that the body gradually adapts to increasing and decreasing UV doses, that sunburning should be avoided, and that it should be in the middle of the day when the UVB to UVA ratio is highest.[46]


Sun exposure, season and vitamin D have been associated with reduced risk of many types of diseases. Many of the health benefits of sun exposure are due to vitamin D production. However, some beneficial effects are due to non-vitamin D factors, including release of nitric oxide, facilitation of outdoor activities and modulation of gene expression. Research is underway to sort out the various effects of sun exposure and vitamin D on health outcomes. In the meantime, it seems reasonable to spend a moderate amount of time in the sun when the solar elevation angle is greater than 45°, both during the day (near solar noon)47 and throughout the year, depending on latitude.[47] Vitamin D supplements can also be taken to augment sun exposure, especially in winter. The vitamin D level to shoot for is now thought to be above 30 ng/ml (75 nmol/L)[48] but more likely over 40 ng/mL (100 nmol/L).[49],[50],[51],[52]

Note: Marc Sorenson and I are nearing completion of a book entitled “Embrace the Sun”. This book reviews the evidence for the health benefits of sunlight in greater detail and also discusses why the concern regarding the risk of skin cancer and melanoma from sunlight is misplaced/overblown. The book should be available in early-to-mid 2017.


Dr. William Grant. Health benefits of sun exposure: vitamin D and beyond. The Vitamin D Council Blog & Newsletter, 2/1/2017.


[1] Baggerly CA, Cuomo RE, French CB, Garland CF, Gorham ED, Grant WB, Heaney RP, Holick MF, Hollis BW, McDonnell SL, Pittaway M, Seaton P, Wagner CL, Wunch A. Sunlight and vitamin D: Necessary for public health. J Am Coll Nutr. 2015 Jul-Aug;34(4):359-65.

[2] Hoel DG, Berwick M, de Gruijl FR, Holick MF. The risks and benefits of sun exposure 2016.Dermatoendocrinol. 2016 Oct 19;8(1):e1248325 .

[3] Juzeniene A, BrekkeP, DahlbackA, Andersson-Engels S, Reichrath J, MoanK, HolickMF, GrantWB, Moan J. Solar radiation and human health. Reports Progress in Physics, 2011;74:066701.

[4] Juzeniene A, Moan J. Beneficial effects of UV radiation other than via vitamin D production.Dermatoendocrinol. 2012 Apr 1;4(2):109-17. 

[5] Phan TX, Jaruga B, Pingle SC, Bandyopadhyay BC, Ahern GP. Intrinsic Photosensitivity Enhances Motility of T Lymphocytes.Sci Rep. 2016 Dec 20;6:39479.

[6] van der Rhee HJ, de Vries E, Coebergh JW. Regular sun exposure benefits health.Med Hypotheses. 2016 Dec;97:34-37.

[7] Autier P, Boniol M, Pizot C, Mullie, P. Vitamin D status and ill health: a systematic review. Lancet Diabetes & Endocrinology. Jan. 2014;2(1):76-89

[8] http://www.tandfonline.com/doi/pdf/10.4161/19381980.2014.983401

[9] Haugen J, Chandyo RK, Ulak M, Mathisen M, Basnet S, Brokstad KA, Valentiner-Branth P, Shrestha PS, Strand TA. 25-Hydroxy-Vitamin D Concentration Is Not Affected by Severe or Non-Severe Pneumonia, or Inflammation, in Young Children. Nutrients. 2017 Jan 17;9(1). pii: E52.

[10] Pludowski P, Holick MF, Pilz S, Wagner CL, Hollis BW, Grant WB, Shoenfeld Y, Lerchbaum E, Llewellyn DJ, Kienreich K, Soni M. Vitamin D effects on musculoskeletal health, immunity, autoimmunity, cardiovascular disease, cancer, fertility, pregnancy, dementia and mortality- a review of recent evidence. Autoimmun Rev. 2013 Aug;12(10):976-89.

[11] Grant WB. 25-Hydroxyvitamin D and breast cancer, colorectal cancer, and colorectal adenomas: case–control versus nested case–control studies, Anticancer Res. 2015;35(2):1153-60.

[12] Bolland MJ, Grey A, Gamble GD, Reid IR. Calcium and vitamin D supplements and health outcomes: a reanalysis of the Women’s Health Initiative (WHI) limited-access data set.Am J Clin Nutr. 2011 Oct;94(4):1144-9.

[13] Lappe JM, Travers-Gustafson D, Davies KM, Recker RR, Heaney RP. Vitamin D and calcium supplementation  reduces cancer risk: results of a randomized trial.Am J Clin Nutr. 2007 Jun;85(6):1586-91.

[14] Lappe J, Travers-Gustafon D, Garland C, Heaney R, Recker R, Watson P. Vitamin D3 and calcium supplementation significantly decreases cancer risk in older women. Poster 3352. 0. American Public Health Association 2016 meeting Oct 31, 2016.

[15] Veloudi P, Jones G, Sharman, JE. Effectiveness of vitamin D supplementation for cardiovascular health outcomes. Pulse, 2016;4:193-207.

[16] Grant WB. A review of the role of solar ultraviolet-B irradiance and vitamin D in reducing risk of dental caries. Dermatoendocrinol. 2011;3(3):193-8.

[17] Hujoel PP. Vitamin D and dental caries in controlled clinical trials: systematic review and meta-analysis. Nutrition Reviews. 2013 Feb;71(2):88-97.

[18] Aloia JF, Li-Ng M. Re: epidemic influenza and vitamin D. Epidemiol Infect. 2007 Oct;135(7):1095-6; author reply 1097-8.

[19] Urashima M, Segawa T, Okazaki M, Kurihara M, Wada Y, Ida H. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr. 2010 May;91(5):1255-60.

[20] Bergman P, Lindh AU, Björkhem-Bergman L, Lindh JD. Vitamin D and Respiratory Tract Infections: A Systematic Review and Meta-Analysis ofRandomized Controlled Trials.PLoS One. 2013 Jun 19;8(6):e65835.

[21] Camargo CA Jr, Ganmaa D, Frazier AL, Kirchberg FF, Stuart JJ, Kleinman K, Sumberzul N, Rich-Edwards JW. Randomized trial of vitamin D supplementation and risk of acute respiratory infection in Mongolia. Pediatrics. 2012 Sep;130(3):e561-7.

[22] Wagner CL, Baggerly C, McDonnell S, Baggerly KA, French CB, Baggerly L, Hamilton SA, Hollis BW. Post-hoc analysis of vitamin D status and reduced risk of preterm birth in two vitamin D pregnancy cohorts compared with South Carolina March of Dimes 2009-2011 rates.J Steroid Biochem Mol Biol. 2016 Jan;155(Pt B):245-51.

[23] Chowdhury R, Kunutsor S, Vitezova A, Oliver-Williams C, Chowdhury S, Kiefte-de-Jong JC, Khan H, Baena CP, Prabhakaran D, Hoshen MB, Feldman BS, Pan A, Johnson L, Crowe F, Hu FB, Franco OH. Vitamin D and risk of cause specific death: systematic review and meta-analysis of observational cohort and randomised intervention studies. BMJ. 2014 Apr 1;348:g1903.

[24] Grant WB, Whiting SJ, Schwalfenberg GK, Genuis SJ, Kimball SM. An Estimate of the Economic Benefit of Increasing 25-hydroxyvitamin D Concentrations of Canadians to or above 100 nmol/L. Dermatoendocrin. 2016;8(1):e1248324.

[25] Lucas RM, Ponsonby AL, Dear K, Valery PC, Pender MP, Taylor BV, Kilpatrick TJ, Dwyer T, Coulthard A, Chapman C, van der Mei I, Williams D, McMichael AJ. Sun exposure and vitamin D are independent risk factors for CNS demyelination. Neurology. 2011 Feb 8;76(6):540-8.

[26] Wang Y, Marling SJ, McKnight SM, Danielson AL, Severson KS, Deluca HF. Suppression of experimental autoimmune encephalomyelitis by 300-315nm ultraviolet light.Arch Biochem Biophys. 2013 Aug 1;536(1):81-6.

[27] Wang Y, Marling SJ, Beaver EF, Severson KS, Deluca HF. UV light selectively inhibits spinal cord inflammation and demyelination in experimental autoimmune encephalomyelitis.Arch Biochem Biophys. 2015 Feb 1;567:75-82.

[28] Grant WB, Bhottoa HP, Boucher BJ. Seasonal variations of U.S. mortality rates: Roles of solar ultraviolet-B doses, vitamin D, gene expression, and infections. J Steroid Biochem Mol Biol. epub Jan. 11, 2017 10.1016/j.jsbmb.2017.01.003

[29] Kroll MH, Bi C, Garber CC, Kaufman HW, Liu D, Caston-Balderrama A, Zhang K, Clarke N, Xie M, Reitz RE, Suffin SC, Holick MF. Temporal Relationship between Vitamin D Status and Parathyroid Hormone in the United States.PLoS One. 2015 Mar 4;10(3):e0118108.

[30] Dopico XC, Evangelou M, Ferreira RC, Guo H, Pekalski ML, Smyth DJ, Cooper N, Burren OS, Fulford AJ, Hennig BJ, Prentice AM, Ziegler AG, Bonifacio E, Wallace C, Todd JA. Widespread seasonal gene expression reveals annual differences in human immunity and physiology.Nat Commun. 2015 May 12;6:7000.

[31] Goldinger A, Shakhbazov K, Henders AK, McRae AF, Montgomery GW, Powell JE. Seasonal effects on gene expression, PloS one 10(5) (2015) e0126995.

[32] Hossein-Nezhad A, Spira A, Holick MF. Influence of vitamin d status and vitamin d3 supplementation on genome wide expression of white blood cells: a randomized double-blind clinical trial. PLoS One. 2013;8(3):e58725.

[33] Donneyong MM, Taylor KC, Kerber RA, Hornung CA, Scragg R. Is outdoor recreational activity an independent predictor of cardiovascular disease mortality – NHANES III?Nutr Metab Cardiovasc Dis. 2016 Aug;26(8):735-42

[34] Shore-Lorenti C, Brennan SL, Sanders KM, Neale RE, Lucas RM, Ebeling PR. Shining the light on sunshine: a systematic review of the influence of sun exposure on type 2 diabetes mellitus-related outcomes. Clin Endocrinol 2014;81:799-811.

[35] Beauchemin K and Hays P.  Dying in the dark: sunshine, gender and outcomes in myocardial infarction.  J R Soc Med. 1998;91(7):352–54. 

[36] Godar DE, Landry RJ, Lucas AD. Increased UVA exposures and decreased cutaneous vitamin D3 levels may be responsible for the increasing incidence of melanoma. Med Hypothesis  2009 Apr;72(4):434-43.

[37] Moukayed M, Grant WB. Molecular link between vitamin D and cancer prevention. Nutrients. 2013;5:3993-4023.

[38] Rebel H, der Spek CD, Salvatori D, van Leeuwen JP, Robanus-Maandag EC, de Gruijl FR.UV exposure inhibits intestinal tumour growth and progression to malignancy in intestine-specific Apc mutant mice kept on low vitamin D diet.Int J Cancer. 2015 Jan 15;136(2):271-7.

[39] Weller RB. The health benefits of UV radiation exposure through vitamin D production or non-vitamin D pathways. Blood pressure and cardiovascular disease.Photochem Photobiol Sci. 2016 Dec 23. doi: 10.1039/c6pp00336b. [Epub ahead of print]

[40] Marshall JE, Byrne SN. Does sunlight protect us from cancer?Photochem Photobiol Sci. 2017 Jan 19. doi: 10.1039/c6pp00332j. [Epub ahead of print]

[41] Abhimanyu, Coussens AK. The role of UV radiation and vitamin D in the seasonality and outcomes of infectious disease.Photochem Photobiol Sci. 2017 Jan 12. doi: 10.1039/c6pp00355a. [Epub ahead of print]

[42] Grant WB. In defense of the sun: An estimate of changes in mortality rates in the United States if mean serum 25-hydroxyvitamin D levels were raised to 45 ng/mL by solar ultraviolet-B irradiance. Dermatoendocrinol. 2009;1(4):207-14.

[43] Chang YM, Barrett JH, Bishop DT, Armstrong BK, Bataille V, Bergman W, et al. Sun exposure and melanoma risk at different latitudes: a pooled analysis of 5700 cases and 7216 controls. Int J Epidemiol. 2009 Jun;38(3):814-30.

[44] Grant WB. Role of solar UV irradiance and smoking in cancer as inferred from cancer incidence rates by occupation in Nordic countries. Dermatoendocrinol. 2012;4(2):203-11.

[45] Gorham ED, Mohr SB, Garland CF, Chaplin G, Garland FC. Do sunscreens increase risk of melanoma in populations residing at higher latitudes? Ann Epidemiol. 2007 Dec;17(12):956-63.

[46] Grigalavicius M, Moan J, Dahlback A, Juzeniene A. Daily, seasonal, and latitudinal variations in solar ultraviolet A and B radiation in relation to vitamin D production and risk for skin cancer.Int J Dermatol. 2016 Jan;55(1):e23-8.

[47] Engelsen O. The relationship between ultraviolet radiation exposure and vitamin D status. Nutrients. 2010 May;2(5):482-95.

[48] Holick MF, Binkley NC, Bischoff-Ferrari HA, Gordon CM, Hanley DA, Heaney RP, Murad MH, Weaver CM. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab, 2011 Jul;96(7):1911-30.

[49] Garland CF, Kim JJ, Mohr SB, Gorham ED, Grant WB, Giovannucci EL, Baggerly L, Hofflich H, Ramsdell J, Zeng K, Heaney RP.Meta-analysis of all-cause mortality according to serum 25-hydroxyvitamin D. Am J Pub Health. 2014 Aug;104(8):e43-50.

[50] Grant WB, Whiting SJ, Schwalfenberg GK, Genuis SJ, Kimball SM. An Estimate of the Economic Benefit of Increasing 25-hydroxyvitamin D Concentrations of Canadians to or above 100 nmol/L. Dermatoendocrin. 2016;8(1):e1248324.

[51] Hollis BW, Wagner CL. Vitamin D requirements and supplementation during pregnancy. Curr Opin Endocrinol Diabetes Obes. 2011 Dec;18(6):371-5.

[52] McDonnell SL, Baggerly C, French CB, Baggerly LL, Garland CF, Gorham ED, Lappe JM, Heaney RP. Serum 25-Hydroxyvitamin D Concentrations ≥40 ng/ml Are Associated with >65% Lower Cancer Risk: Pooled Analysis of Randomized Trial and Prospective Cohort Study.PLoS One. 2016 Apr 6;11(4):e0152441.

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