Vitamin D in Japan: best months for sun and a travel guide

The best months for vitamin D in Japan are November. In November, a full dose of about 1,000 IU takes around 11 minutes at midday for skin type III at age 30, with 4.7 usable sun hours a day. For a beach stay it is too cool from December to March and rainy or stormy from April to October.

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Japan month by month

Japan is rated at its median coastal place, for skin type III at age 30. Click a month for the details.

Month	Rating	Sun window	Peak UV	Full dose, age 30	Full dose, age 65	Afternoon high	Rainy days
January	Too cold	4.1 h	4.3	12 min	23 min	20°C	6/30
February	Too cold	5.1 h	5.1	10 min	20 min	21°C	11/30
March	Too cold	6.0 h	6.5	8 min	15 min	21°C	13/30
April	Bad weather	7.3 h	7.6	7 min	13 min	24°C	19/30
May	Bad weather	6.9 h	7.4	7 min	14 min	27°C	21/30
June	Bad weather	6.6 h	7.0	8 min	14 min	27°C	18/30
July	Bad weather	8.5 h	8.3	6 min	12 min	31°C	23/30
August	Bad weather	8.3 h	8.2	7 min	12 min	31°C	23/30
September	Bad weather	7.7 h	7.5	7 min	13 min	31°C	23/30
October	Bad weather	6.6 h	6.5	8 min	15 min	29°C	18/30
November	Good	4.7 h	4.8	11 min	21 min	25°C	15/30
December	Too cold	2.9 h	3.5	15 min	29 min	21°C	12/30

Sun window is the number of hours a day with UV Index 2.5 or higher. Full dose is the minutes at midday for about 1,000 IU of vitamin D with a quarter of the body bare, for skin type III. Rainy days are days with at least 1 mm out of 30.

Travel guide: why go to Japan

Why go

Japan's southern islands of Okinawa have warm turquoise water and a relaxed culture distinct from mainland Japan.

Best for

Couples, divers, families and travellers who want a calmer side of Japan.

What to expect

A hot, humid summer with typhoon risk from July to October, and mild winters that are too cool for swimming. The swimming season is April to October. English is limited outside the big hotels.

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Places in Japan

Each place has its own climate, so its best months can differ from the country as a whole.

Naha best: Excellent

Okinawa's capital of markets, a castle and easy access.

Best for city-break fans, foodies

Best months May, October, November · Avoid too cool from December to March; rainy or stormy in April and from June to September

Ishigaki best: Good

Gateway island to the Yaeyama group, with snorkelling and manta rays.

Best for divers, couples

Best months February, March · Avoid too cool from December to January; rainy or stormy from April to November

Miyakojima best: Good

Flat coral island with some of the clearest water in Japan.

Best for couples, divers, families

Best months February, March, November · Avoid too cool from December to January; rainy or stormy from April to October

Zamami best: Excellent

Small island with whale watching in winter and bright blue sea.

Best for divers, whale watchers

Best months May, July, October, November · Avoid too cool from December to March; rainy or stormy in April and in June and from August to September

Onna best: Good

Resort coast of Okinawa with long hotel beaches.

Best for families, couples

Best months November · Avoid too cool from December to March; rainy or stormy from April to October

Questions about vitamin D in Japan

When is the best time to visit Japan for vitamin D?

The best months for vitamin D in Japan are November. In November, a full dose of about 1,000 IU takes around 11 minutes at midday for skin type III at age 30, with 4.7 usable sun hours a day.

Can you get vitamin D from the sun in Japan in December?

Yes, but slowly. In December a full dose takes about 15 minutes at midday for skin type III at age 30, with 2.9 usable hours a day.

How long do I need in the sun in Japan?

In November, the best month, about 11 minutes at midday with a quarter of the body bare, for skin type III at age 30; about 21 minutes at age 65. Darker skin needs longer and fair skin burns sooner, so keep sessions short. This is an estimate for planning, not medical advice.

Which months should I avoid in Japan?

For a beach stay, avoid the months when it is too cool from December to March and rainy or stormy from April to October.

What is the best place in Japan for vitamin D?

In November the strongest sun of the places we rate is around Naha. Each place has its own rating, so open the place list to compare them.