What are the common misunderstandings about vitamin D and sunlight?

This answer is a draft. It stays unpublished until legal review and source verification are complete.

The claim that "sunscreen leaves you short of vitamin D" is raised in many countries as a counter to sun-protection campaigns. In Japan the 2025 Dietary Reference Intakes raised the adequate intake for vitamin D, and interest has grown.

In numbers

• A 2013 study by the National Institute for Environmental Studies and Tokyo Kasei University published, by season and region, the sunlight exposure time needed to produce 10 μg of vitamin D. The range is wide: a few minutes in summer, more than an hour in northern Japan in winter.
• The Ministry of the Environment's UV manual states that UV protection and getting enough vitamin D are not in conflict, and that everyday exposure plus food is enough.
• Groups where vitamin D shortage is a concern: people who spend their days mostly indoors, northern Japan in winter, older people, people who do not eat fish, and infants (paediatricians advise vitamin D supplementation for breastfed babies).

[Verify] Check the adequate intake against the 2025 Dietary Reference Intakes, the sunlight exposure times against the National Institute for Environmental Studies release (2013), and the food values against the Standard Tables of Food Composition in Japan (8th revised edition).

Misunderstanding 1｜Sunscreen causes vitamin D deficiency

Everyday exposure (face, hands, a few minutes on the commute) plus food is enough. The Ministry of the Environment's position is to recommend UV protection while covering vitamin D from food and everyday exposure.

Misunderstanding 2｜Sunbathe longer and you make more

Production levels off at a certain amount, and any further UV is only a burden on the skin. In summer, a few to ten-odd minutes is enough.

Misunderstanding 3｜Sunlight through a window works too

UVB, the part of sunlight involved in making vitamin D, barely passes through window glass. Little is produced sitting by a window indoors.

Misunderstanding 4｜Take plenty in supplements and you will be healthier

There is a tolerable upper intake of 100 μg, and excess causes hypercalcaemia (too much calcium in the blood). Exceeding the limit with a normal diet plus a supplement is rare, but for high-dose supplements, ask a doctor or pharmacist.

Misunderstanding 5｜Japanese people eat fish, so they are never short

Fish consumption is falling, and younger generations are generally described as taking in less than the adequate intake. Fish two or three times a week, mushrooms and eggs are the realistic way to get enough.

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Sources

• Ministry of Health, Labour and Welfare, *Dietary Reference Intakes for Japanese (2025 edition)* [日本人の食事摂取基準（2025年版）] (vitamin D)

https://www.mhlw.go.jp/stf/newpage_44138.html

• National Institute for Environmental Studies, *Estimating the sunlight exposure time needed to produce the vitamin D the body requires* [体内で必要とするビタミンD生成に要する日照時間の推定] (2013)

https://www.nies.go.jp/whatsnew/2013/20130830/20130830.html

• Ministry of the Environment, *UV Environmental Health Manual 2020* [紫外線環境保健マニュアル2020] (relationship with vitamin D)

https://www.env.go.jp/chemi/uv/uv_manual.html

⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.

About this article

What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.

This is general information. Results vary from person to person and depend on your own conditions and surroundings.

Please decide for yourself, using your own judgement, whether any of this suits your situation. We cannot accept responsibility for any damage, loss or injury arising from following this article.

This article is not meant to diagnose or manage any specific medical condition. If you are worried about your health, see a doctor rather than relying on your own judgement.

Sources

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