For some time now I have been following the work of dermatologist, Dr Richard Weller from the University of Edinburgh. His research is challenging the fundamental dermatological belief that we should stay out of the sun as it is harmful to health. He appeared on a www.foot.expert webinar back in 2022 proposing that the message should change. In a forthcoming paper to be published in the prestigious Journal of Investigative Dermatology, Dr Weller insists it’s time for a rethink on sunshine [1]. In this blog I will try and capture the essence of his argument which has some surprising aspects.
Introduction
It’s been known for many years that excessive UV exposure may lead to the development of skin cancers including melanoma. With the consistent year on year rise in melanoma and keratinocyte cancers (like basal cell carcinoma and squamous cell carcinoma) the health message over the decades has been broadly “stay out of the sun”. As we have known for some time though, sunlight on the skin is required to manufacture vitamin D [2]. If we are spending more time in the shade, then the production of vitamin D will reduce.
Vitamin D supplementation has little effect on health
The health benefits of having good vitamin D levels have been reported widely in many studies but as Richard Weller contests, these claims have been misinterpreted. Numerous diseases including hypertension, cardiovascular disease, cerebrovascular disease, metabolic disease, multiple sclerosis, and cancer, have all been associated with low measured vitamin D levels. Today, we have many middle-aged people taking vitamin D supplements, during the winter months in high doses as a means of acquiring the health benefits of the vitamin.
But does vitamin supplementation actually give you these benefits? Two of the largest randomised placebo controlled trials of vitamin D supplementation [3, 4] study (with over 5000 participants) have shown that vitamin D supplementation failed to reduce the incidence of cardiovascular disease, cancer along with no reduction in depression, falls and fractures, frailty, atrial fibrillation or strokes. So, what was happening? We know the positive health benefits of vitamin D but these are not being observed in people who supplement their vitamin D levels.
Sunlight improves health
Dr Weller has been researching the effects of sunlight on the skin and within this lies the answer. The first thing he discusses in his paper is that sunlight is actually good for you. He cites studies where a cohort of middle age Swedish women are observed over many years examining their sun exposure history. The work clearly showed that those who spent the highest amount of time in the sun, 25 years later, were more likely to be alive and healthier (despite having higher rates of melanoma) than those who avoided the sun. This was largely down to lower rates of cardio-vascular disease in the sun seekers [5, 6].
His own subsequent research on white UK population data drew identical conclusions. Those who showed sun seeking behaviours had a lower risk of all causes of death (including cardio-vascular disease and cancer). In addition, they had higher levels of vitamin D. He goes on to identify that levels of hypertension (a major risk factor for cardio-vascular events and mortality) are lower in the summer months than in the winter. Moreover, those with lower blood pressure have higher vitamin D levels than their hypertensive counterparts. However, supplementation with vitamin D has no effect, suggesting an alternative mechanism for this sunlight effect.
How does sunlight improve health?
Dr Weller’s research team and a second group independently demonstrated that low level UVA irradiation of human volunteers releases nitric oxide (NO) from cutaneous stores to the circulation where it lowers systemic blood pressure through arterial dilatation, independently of temperature. They used UVA because it does not synthesise vitamin D, and the vitamin D independent nature of UV-induced BP reduction could be demonstrated. The UV energy of natural sunlight required to mobilise NO from keratinocytes is below that which leads to detectable DNA damage.
In addition, he presents some evidence showing how for other diseases such as diabetes mellitus, multiple sclerosis, ischaemic heart disease and COVID-19 vary according to latitude and seasonality suggesting that sun exposure has likely benefits yet undocumented. Coincidentally, none of these conditions have been shown to improve with vitamin D supplementation.
Where does that leave vitamin D?
Vitamin D does have health benefits, but as research shows this effect is predominantly seen in those who are vitamin D deficient [3] – not in those with normal levels taking supplements. For example, in preventing rickets in those with reduced vitamin D levels.
Skin colour and UV-generated vitamin D
Of particular importance in this whole scenario is skin colour. Skin of colour contains more melanin than pale skin types, consequently much of the UV is absorbed by the melanin in the skin, and so less is likely potentially to trigger nitric oxide release. The paper quotes from an earlier study by Dr Weller from the United States of patients undergoing dialysis who have regular BP measurements [7]. It shows the UV effect on lowering blood pressure is less marked in darker skin types. Consequently, Dr Weller comments this may be reflected in the higher rates of cardiovascular events in darker skinned individuals as black skin is significantly more protected from UV A and B induced changes.
Sunlight is good for you!
This work represents a major step forward in understanding the interaction of sunlight and its positive effects on human health. If you compare the number of deaths through melanoma versus cardio-vascular disease, you will see that skin cancer mortality is dwarfed by the statistics for heart attacks and strokes. So, on that basis, Dr Weller suggests the public message to stay out of the sun may need modification if we are to improve the health of a population. As Richard said when asked for his advice on the webinar, he replied “Sit in the sun, it’s good for you, but don’t get burned”. Good advice to follow until we have a consensus from researchers in this field on the correct message.
Final thoughts
There are a lot more questions to be answered here and as Richard alludes to, there are differences in UV levels based on latitude and responses to sunlight vary according to one’s natural skin colour. Consequently, more research is required to fully understand this phenomenon. But, for now enjoy the sun when it appears – but don’t get burned.
Resources:
You can watch Richard’s TED talk discussing the health benefits of sunshine on youtube: https://www.youtube.com/watch?v=Lh9lDWPMWrM
You can also watch his appearance on foot.expert in the videos section of the website:
References
The full paper can be downloaded here for free. CC-BY creative commons licence.
1. Weller RB: Sunlight: Time for a Rethink? J Invest Dermatol 2024.
2. Bikle DD: Vitamin D: Production, Metabolism and Mechanisms of Action. In Endotext. Edited by Feingold KR, Anawalt B, Blackman MR, Boyce A, Chrousos G, Corpas E, de Herder WW, Dhatariya K, Dungan K, Hofland J, et al. South Dartmouth (MA): MDText.com, Inc.
Copyright © 2000-2024, MDText.com, Inc.; 2000
3. Scragg RKR: Overview of results from the Vitamin D Assessment (ViDA) study. J Endocrinol Invest 2019, 42:1391-1399.
4. Scragg R, Stewart AW, Waayer D, Lawes CMM, Toop L, Sluyter J, Murphy J, Khaw KT, Camargo CA, Jr.: Effect of Monthly High-Dose Vitamin D Supplementation on Cardiovascular Disease in the Vitamin D Assessment Study : A Randomized Clinical Trial. JAMA Cardiol 2017, 2:608-616.
5. Lindqvist PG, Epstein E, Landin-Olsson M, Ingvar C, Nielsen K, Stenbeck M, Olsson H: Avoidance of sun exposure is a risk factor for all-cause mortality: results from the Melanoma in Southern Sweden cohort. J Intern Med 2014, 276:77-86.
6. Lindqvist PG, Epstein E, Nielsen K, Landin-Olsson M, Ingvar C, Olsson H: Avoidance of sun exposure as a risk factor for major causes of death: a competing risk analysis of the Melanoma in Southern Sweden cohort. J Intern Med 2016, 280:375-387.
7. Weller RB, Wang Y, He J, Maddux FW, Usvyat L, Zhang H, Feelisch M, Kotanko P: Does Incident Solar Ultraviolet Radiation Lower Blood Pressure? J Am Heart Assoc 2020, 9:e013837.
