This is the argument most often used to justify going without protection, and it is the one where the United Kingdom's own public health guidance settles the matter most cleanly, in a direction that has nothing to do with sunscreen.
The mechanism, briefly
Ultraviolet B striking skin converts a cholesterol derivative in the epidermis into a precursor of vitamin D, which is then further processed in the liver and kidneys. Since ultraviolet B is also the wavelength band that a sunscreen most strongly attenuates, the concern is coherent on its face: block the radiation and you block the synthesis.
Two things complicate it. First, ultraviolet B reaching the ground varies enormously with latitude, season, time of day and cloud, and at British latitudes there is a substantial part of the year during which the available ultraviolet B is insufficient for meaningful synthesis at any level of exposure. Second, no sunscreen blocks all ultraviolet, and people do not apply sunscreen at the density used in the test method.
The position in the United Kingdom
UK public health guidance addresses vitamin D through diet and supplementation, not through sun exposure. The Scientific Advisory Committee on Nutrition reviewed the evidence and its report underpins the current recommendations, which the NHS sets out. The reason the guidance takes that form is precisely that sunlight at these latitudes cannot be relied upon through the year.
That is the key structural point. The vitamin D question in Britain is not answered by adjusting sun exposure, because for a large part of the year adjusting sun exposure cannot answer it. It is answered by dietary guidance, which is why this publication points at the NHS and stops.
Vitamin D intake, testing and supplementation are clinical and nutritional matters. The NHS publishes the current recommendations, including who should consider a supplement and at what time of year, and there are groups for whom specific advice applies. If you are concerned about your vitamin D status, or you are considering a supplement, speak to a pharmacist or your GP rather than acting on anything read here. This publication gives no advice on supplementation.
What the evidence on sunscreen use shows
Reviews of studies examining sunscreen use and vitamin D status have generally not found that typical use causes deficiency. The explanations are straightforward. People apply considerably less than the test density, so a substantial proportion of ultraviolet B still reaches the skin. Sunscreen is applied to exposed areas and not to the whole body. And people who use sunscreen are frequently people who spend time outdoors.
Controlled studies of very high protection products applied at the tested density can show effects on synthesis, which is what you would expect, and which is a different question from whether ordinary use produces deficiency in a population.
Wearing sunscreen causes vitamin D deficiency
- What would have to be true
- That typical sunscreen use reduces ultraviolet B reaching skin sufficiently to lower vitamin D status to a deficient level.
- That sun exposure is the operative variable for vitamin D status in the population in question.
- What is established
- Ultraviolet B drives cutaneous vitamin D synthesis and is the band a sunscreen most strongly attenuates.
- Reviews of studies of sunscreen use and vitamin D status have generally not found that typical use causes deficiency.
- UK public health guidance addresses vitamin D through diet and supplementation because sunlight at these latitudes is insufficient for a large part of the year, irrespective of sunscreen.
- What is not established
- That typical sunscreen use produces deficiency.
- That reducing sun protection is a recommended route to vitamin D status in the United Kingdom. Public health guidance does not take that form.
Why this argument circulates in this category specifically
It appears more often in natural sun care than elsewhere, and the reason is structural rather than scientific. A category built on the idea that intervention is suspect and nature is benign has an obvious use for an argument in which sun exposure is a nutrient and sunscreen is what stands between you and it.
The difficulty is that the argument proves too much. If unprotected exposure is a nutritional strategy, it is one whose dose cannot be controlled, whose benefit plateaus, and whose cost is cumulative and irreversible. Ultraviolet is a known human carcinogen, and the relationship between exposure and skin cancer risk is one of the better established in cancer epidemiology, which Cancer Research UK sets out clearly.
Meanwhile the alternative route is a dietary one that is inexpensive, controllable and recommended by the relevant public health bodies. When a nutrient can be obtained by a controllable route and by an uncontrollable one that carries a carcinogenic exposure, the argument for the second requires more than it usually receives.
The variable that the argument usually leaves out
Cutaneous synthesis of vitamin D varies substantially between individuals, and melanin is one of the reasons. Higher constitutive melanin attenuates ultraviolet B in the epidermis, which reduces synthesis for a given exposure. That is a well described physiological difference, and it is part of why UK public health guidance identifies groups for whom particular advice applies.
The relevance here is that an argument which recommends unprotected sun exposure as a route to vitamin D produces very different implications for different people, and it does so in a direction that is not intuitive: the person who would need the most exposure to achieve a given synthesis is also the person for whom the argument is most often assumed to be unnecessary. That is a good illustration of why individual advice is individual, and why it belongs with a clinician who knows the person in front of them.
Age matters too, as does how much skin is habitually covered. None of these variables is addressed by a general statement about sunscreen, which is the point.
What is genuinely unresolved
Several things, and they are worth stating because the subject is not simple.
- Optimal status. What blood level constitutes sufficiency has been debated, and thresholds differ between bodies and over time.
- Non skeletal effects. Vitamin D's role beyond bone health has generated a very large literature and a good deal of disappointing trial evidence. NICE and other bodies keep this under review.
- Individual variation. Skin tone, age, body composition, covering practices and latitude all affect synthesis substantially.
None of these is resolved by a decision about sunscreen, and none of them is something this publication is competent to advise on.
The summary
The mechanism behind the concern is real. The claim that ordinary sunscreen use causes deficiency is not supported. The United Kingdom answers the vitamin D question through diet and supplementation, because at these latitudes sunlight cannot answer it for much of the year. And anything to do with your own status, testing or supplementation is a conversation with a pharmacist or a GP, who can look at your circumstances in a way that no article can.
Because the vitamin D argument is used to sell an idea about sun exposure, and because the reader deserves to know that the public health system has already answered the question by a route that does not involve going without protection. The answer is boring and it is on the NHS website.
A final boundary
This publication is about the chemistry of a cosmetic category and the claims that category makes. Vitamin D is nutrition and public health. The only reason it appears here is that it is deployed as an argument about sunscreen, and the correction is that it is not an argument about sunscreen at all. Having made that point, this article stops and points at the NHS, the Scientific Advisory Committee on Nutrition report that underpins the guidance, and NICE.