Sun Exposure - The Fine Line Between Vitamin D Necessity and Cancer Risk

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The sun is the giver of all life on our planet. Through photosynthesis the sun triggers nutrient production in plants. Plants then feed herbivores, which in turn feed carnivores.

Humans have evolved to live with the sun. Its rhythm tunes our circadian cycle, helping us secrete the right hormones at the right time to wake up and fall asleep well.

When bathed in sunrays, our skin switches on the production of Vitamin D, a very important nutrient.

But as is occasionally the case in biology, a good thing can have dark sides. In this case, it’s the potential damage to our retinas, faster skin aging, and the risk of skin cancer.

In this article we’ll shed light on the latest science about the sweet spot between benefit and harm.

 Sun exposure - between Vitamin D necessity and Cancer Risk

The Importance of Vitamin D

In discussing Vitamin D, the reference in this article is specifically to Vitamin D3. We’ll just refer to it as, “Vitamin D.”

Vitamin D affects the expression of more than 1000 genes in the human body.[1] It’s an extremely important nutrient, associated with lower incidence of cancer, stronger bones, and clearer minds. In a major meta-analysis scientists found that Vitamin D deficiency was associated with more severe Covid symptoms.[2] Still, it is estimated that roughly 40% of Americans are deficient in this important vitamin.[3]

We can produce Vitamin D in our skin, supplement it, or obtain it from a few foods, mainly fish, like sardines, sockeye salmon, and trout, but not in sufficient amounts.

While Vitamin D recommendations vary, research has shown that blood levels of about 40-60 ng/ml tend to be optimal in many respects.[4] [5]


UVB Light – A Friend and A Foe

There is a small portion of sunrays that is dangerous. It’s made of ultraviolet (UV) light, of which UVA and UVB are of concern. There’s also UVC, but it’s blocked by the ozone layer.[6]

UVA, constituting 95% of the UV light that reaches the ground, ages our skin, breaks down our collagen, and causes cell death and inflammation.[7]

UVB, making up the remaining 5%, causes sunburns and plays a key role in skin cancers.[8]

At the same time, UVB is necessary for Vitamin D production in our skin.

UVB can be blocked by a glass window, thick clouds, and the application of sunblock on the skin.


The Fine Line Between Cancer Risk and Sufficient Vitamin D

The more intense the sun is, the more efficiently your skin produces Vitamin D, but also the more likely you are to get burned, which increases your risk of cancer in the long run.[9]

Therefore, your exposure should be short enough to avoid damage but long enough to produce your daily requirement of Vitamin D (which currently stands at 20mcg, or 800 IU).[10]

Where is the sweet spot?

That depends on several factors.

1) What time of the day it is. Between 10am and 4pm sunlight is most intense.

2) How far from the equator you are. In northern and southern latitudes, towards the poles, the sun shines at lower angles, making its rays less intense.

3) How far up you are. The higher the altitude, the more intense the sun.

4) How dark your skin is. Darker skin, containing more sun-blocking melanin, can sustain more time in the sun before getting burned; it also requires more time in the sun to produce Vitamin D.

5) What season of the year it is. In the winter the sun shines at lower angles and is less intense.

So, if you are of northern European descent, hiking at 1pm on the Kilimanjaro in the summer, then 3 minutes in the sun may suffice. There is a whole continuum between this extreme scenario and being in Alaska in the winter. A very rough guideline is 10-30 minutes of midday exposure, several times a week.

The best way to judge is to monitor your skin’s coloration. As a rule of thumb, stay out in the sun until your skin just about starts turning pink. However, you may not notice a change until you move to a shaded area and give it a few minutes. Also, visible change in coloration indicates that your skin already began sustaining damage. So a fine line, if it exists, is very fine indeed.

Another trick is feeling how hot your skin is. If it feels hotter than usual, then it’s a good bet that it’s time to cut your exposure short.

An extra confounder is age. By the age of 80, the production of Vitamin D from the sun is 200% lower than among teenagers.[11] So for an older individual concerned about cancer, staying in the sun presents a needless risk with little reward.


At this point you may start wondering whether sun exposure is worth it at all, particularly if you can obtain Vitamin D in other ways. If that’s your thinking, then great minds think alike.


Steps To Protect Yourself from Sun Damage

If you already supplement with Vitamin D, and your highest priority is protection from the sun, then you have several options.  

To protect your eyes, it’s best to wear sunglasses during high glare. However, if you have just traveled across time zones, trying to deal with jetlag, then sunglasses will only make it difficult. You need a decent amount of daytime glare to readjust your circadian cycle. In this case, your best option is to wear a cap or a wide-brim hat to shield your eyes from direct sunlight.

However, if you are in an area of bright reflection, as from sand or snow, then you may want to wear sunglasses anyway, because the damage to the retinas can also come from below. The same is true for skin damage.

When it comes to skin protection, the first tool that comes to mind is sunblock. We highly recommend avoiding a chemical sunblock because it can disrupt your hormonal system.[12] Opt, instead, for a natural sunblock and UV-protective lip balm that don’t contain any harmful chemicals.

We found this natural sunblock (and other skincare products) from at a vegan fest in New Jersey, where they had a booth right next to ours.

Natural sunblock from

Another option is wearing long-sleeve UV-protective clothing, and smearing natural sunblock on the few skin areas that are still exposed, namely, the face and hands.

The American Academy of Dermatology “does not recommend getting vitamin D from sun exposure or indoor tanning.”[13] As implied above, this is our conclusion too.


[1] Carlberg, Carsten. “Vitamin D: A Micronutrient Regulating Genes.” Current pharmaceutical design vol. 25,15 (2019): 1740-1746. doi:10.2174/1381612825666190705193227

[2] Pereira, Marcos et al. “Vitamin D deficiency aggravates COVID-19: systematic review and meta-analysis.” Critical reviews in food science and nutrition, 1-9. 4 Nov. 2020, doi:10.1080/10408398.2020.1841090

[3] Forrest, Kimberly Y Z, and Wendy L Stuhldreher. “Prevalence and correlates of vitamin D deficiency in US adults.” Nutrition research (New York, N.Y.) vol. 31,1 (2011): 48-54. doi:10.1016/j.nutres.2010.12.001

[4] Grant, William B, and Meis Moukayed. “Vitamin D3 from Ultraviolet-B Exposure or Oral Intake in Relation to Cancer Incidence and Mortality.” Current nutrition reports vol. 8,3 (2019): 203-211. doi:10.1007/s13668-019-0262-5

[5] Speer, Gábor. “A D-vitamin jelentősége neurológiai kórképekben és a neurorehabilitációban: a dementiától a sclerosis multiplexig. I. rész: a D-vitamin szerepe a sclerosis multiplex megelőzésében és kiegészítő kezelésében” [Impact of vitamin D in neurological diseases and neurorehabilitation: from dementia to multiple sclerosis. Part I: the role of vitamin D in the prevention and treatment of multiple sclerosis]. Ideggyogyaszati szemle vol. 66,9-10 (2013): 293-303.


[7] Wang, Pei-Wen et al. “Comparison of the Biological Impact of UVA and UVB upon the Skin with Functional Proteomics and Immunohistochemistry.” Antioxidants (Basel, Switzerland) vol. 8,12 569. 20 Nov. 2019, doi:10.3390/antiox8120569




[11] MacLaughlin, J, and M F Holick. “Aging decreases the capacity of human skin to produce vitamin D3.” The Journal of clinical investigation vol. 76,4 (1985): 1536-8. doi:10.1172/JCI112134

[12] Refer to our article about Endocrine Disrupting Chemicals.


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