: Does the use of sunscreen inhibit Vitamin D production? Vitamin D is produced in the skin when exposed to sunlight. Therefore, when using sunscreen on the skin, is Vitamin D production inhibited?

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Vitamin D is produced in the skin. There are two subtypes of UV radiation: UVA and UVB. UVA is primarily responsible for photoaging, and UVB for the superficial burning that results from sun exposure (2).

UVB electromagnetic radiation converts 7-dehydrocholestrol to pre-vitamin D3, which is then converted into Vitamin D3 (1). Sunscreens with an SPF rating absorb or reflect (depending on the filters used) UVB light (2). Without UVB light, 7-dehydrocholestrol cannot be converted into pre-vitamin D. It may also be of interest to note that glass blocks UVB (but not UVA radiation) and thus has a similar effect on Vitamin D production (1).

In reality, however, people rarely apply sunscreen well enough so that Vitamin D production completely ceases (3).

In short, yes sunscreen does inhibit the production of Vitamin D, although in most cases not to such an extent that Vitamin D deficiency becomes a concern.

References

ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/ www.skincancer.org/prevention/uva-and-uvb www.health.harvard.edu/staying-healthy/6-things-you-should-know-about-vitamin-d

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This has been a controversial question for many years. The current evidence suggests that sunscreen does block a part of Vitamin D production, but with negligible amounts.

Studies have found that by blocking ultraviolet rays, sunscreen limits
the vitamin D we produce. But the question is to what extent.

A few studies have concluded that the effect is significant — a
reduction as great as tenfold. But more recent, randomized studies
that followed people for months and in some cases years suggest that
the effect is negligible. While sunscreen does hamper vitamin D
production, these studies say, it is not enough to cause a deficiency.
[...]
Dr. Lim added that rather than cutting back on sunscreen, people
concerned about vitamin D should consume more foods rich in vitamin D,
like salmon, milk and orange juice.

Source: New York Times Article, Emphasis Mine

Studies cited in the article

Matusoka LY et al. Chronic sunscreen use decreases circulating concentrations of 25-hydroxyvitamin D. A preliminary study. PubMed link
Marks R et al. The effect of regular sunscreen use on vitamin D levels in an Australian population. Results of a randomized controlled trial. PubMed link
Farrerons J et al. Clinically prescribed sunscreen (sun protection factor 15) does not decrease serum vitamin D concentration sufficiently either to induce changes in parathyroid function or in metabolic markers. PubMed link

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In addition to the other answers:

[C]linical studies have never found that everyday sunscreen use leads to
vitamin D insufficiency. In fact, the prevailing studies show that
people who use sunscreen daily can maintain their vitamin D levels.
One of the explanations for this may be that no matter how much
sunscreen you use or how high the SPF, some of the sun’s UV rays reach
your skin. An SPF 15 sunscreen filters out 93 percent of UVB rays, SPF
30 keeps out 97 percent, and SPF 50 filters out 98 percent. This
leaves anywhere from 2 to 7 percent of solar UVB reaching your skin,
even with high-SPF sunscreens. And that’s if you use them perfectly.

Sun Protection and Vitamin D By Skin Cancer Foundation

There are claims that one needs to get a certain amount of sun
exposure every day in order to produce enough vitamin D to be healthy.
It’s just not true
David J. Leffell, MD, Yale Medicine dermatologist and chief of
Dermatologic Surgery

Vitamin D Myths 'D'-bunked - Yale Medicine