Vitamin D is a nutrient that your body needs to maintain good health. Especially in the winter, we tend to be deficient in vitamin D, so we need to actively consume it. However, many people do not know the specific functions of vitamin D and how much they should take in a day.

Therefore, this time we will explain in detail the function of vitamin D and the recommended intake. We will also introduce reasons why you should actively consume it in winter, so please refer to it.

Functions of vitamin D and why it is important to take it in winter

Here we will explain in detail the function of vitamin D.


● Function of vitamin D

Vitamin D is a nutrient that primarily affects the function of calcium. Consuming appropriate amounts on a daily basis will help maintain your health. If you are concerned about lifestyle measures and eating habits, you should actively adopt this method.


● Why it is important to actively take in vitamin D during the winter season

Winter is a time when it's easy to get sick. In winter, there are many opportunities to turn on the heating, and the temperature difference between outdoors and indoors tends to be large. If the temperature difference is large, the condition of your body will deteriorate and you will be more likely to get sick.

Therefore, vitamin D is recommended. Vitamin D has the effect of regulating the body's health, so it's a good idea to consciously get it from your daily meals.


● Recommended amount of vitamin D to take per day

According to the Ministry of Health, Labor and Welfare's Dietary Intake Standards for Japanese (2020 Edition), the recommended intake of vitamin D is 8.5 μg per day for both men and women over the age of 18. However, the recommended intake of vitamin D varies greatly depending on age.

According to the Japan Osteoporosis Society's "Osteoporosis Prevention and Treatment Guidelines 2015 Edition," the recommended intake of vitamin D for elderly people is 10 to 20 μg per day. Many elderly people have less exposure to sunlight, and it is thought that they produce relatively little vitamin D, so they are given more vitamin D than other age groups.

The tolerable upper limit of vitamin D for both adults and the elderly is 100 µg per day. When taking supplements, be sure to pay attention to the tolerable upper limit of vitamin D.

[Source] “Dietary Intake Standards for Japanese (2020 Edition)” (Ministry of Health, Labor and Welfare)
https://www.mhlw.go.jp/content/10904750/000586553.pdf

[Source] “Vitamin D” (Ministry of Health, Labor and Welfare)
https://www.ejim.ncgg.go.jp/public/overseas/c03/10.html

Reasons for vitamin D deficiency in winter

Sunlight is one of the reasons why vitamin D deficiency tends to occur in winter. Vitamin D is also produced when exposed to sunlight. This is an extremely rare feature since many vitamins can only be obtained through food. From here, we will explain in detail the relationship between vitamin D and sunlight.


● Decrease in daylight hours

In winter, sunlight hours are short, so there are fewer opportunities for exposure to UV rays. If you want to produce vitamin D, you will need to actively sunbathe in winter. The recommended amount of sunbathing time required to produce vitamin D is 15 to 30 minutes.

There are also differences in the recommended amount of sun exposure depending on region, time of day, and season. If you live in northern areas such as Hokkaido, you need to be exposed to sunlight for longer, but if you live in southern areas such as Okinawa, you can produce sufficient amounts of vitamin D even in a short period of time.

The article below details the amount of sunlight exposure required for vitamin D production.

Is it better to get sunlight to generate vitamin D? Approximate time for sunbathing


● Reduced skin exposure through cold protection measures

There are two types of ultraviolet rays: medium-wavelength ultraviolet rays (UV-B) and long-wavelength ultraviolet rays (UV-A). It is the former UV-B that is involved in the production of vitamin D.

UV-B does not pass through clothing, so if the exposed area of your skin is small, it will hinder the production of vitamin D. In winter, we have more chances to wear thick clothes, which makes us more likely to be deficient in vitamin D.


● Decrease in opportunities to go out

In winter, the temperature is low, so we tend to refrain from going out and spend a lot of time indoors. Also, depending on the area, you may not be able to go outside due to poor road conditions.

UV-B cannot pass through clothing or glass. In order to stimulate the production of vitamin D, it is necessary to directly expose your skin to UV rays, so if you go out less often, you will be more likely to become deficient in vitamin D.

An efficient way to get vitamin D in winter

From here, we will introduce how to intake vitamin D efficiently. Let's take in what we can and aim to eliminate vitamin D deficiency.


● Increase opportunities for walking and sunbathing during the day

To get enough sunlight even in winter, it's a good idea to go out during the day when the temperature is high. The amount of ultraviolet rays is low in the early morning and after evening, so daytime is recommended if you want to efficiently generate vitamin D.

Also, because the temperature is higher during the day, you may not need to take excessive measures to protect yourself from the cold. Increase the exposed area of your skin as much as you can to encourage the production of vitamin D.

Furthermore, many people tend to avoid sunbathing as UV rays are said to cause age spots and wrinkles. If you are concerned about aging caused by ultraviolet rays, try exposing only your arms and legs to sunlight.


● Incorporate actively into meals

Foods high in vitamin D include:

・Salted bonito
・Monkfish
・Wood fungus
・Shiitake mushrooms
·salmon

Fish and mushrooms contain a lot of vitamin D. However, not many people eat these on a daily basis, so it is necessary to consciously consume them. In addition, drying food in the sun or cooking it in oil is also effective in order to ingest vitamin D efficiently.

Dried shiitake mushrooms tend to have higher amounts of vitamin D than fresh ones. When eating shiitake mushrooms, we recommend drying them in the sun.

Additionally, vitamin D is a fat-soluble vitamin, so eating it with oil will improve its absorption efficiency. Therefore, cooking methods such as stir-frying and frying are effective.

Ranking of foods rich in vitamin D | Recommended daily intake

[Source] “Japanese Food Standard Composition Table 2020 Edition (8th Edition)” (Ministry of Education, Culture, Sports, Science and Technology)
https://www.mext.go.jp/a_menu/syokuhinseibun/mext_01110.html


● Take advantage of supplements

If you don't get enough vitamin D from your daily diet or sunbathing, one way is to supplement with vitamin D. Some supplements can provide you with the daily amount of vitamin D you need in just one tablet.

When using supplements, care must be taken regarding safety and usage. Supplements are not medicines and should not be used with the expectation of curing a disease. If you suspect that you are sick, please visit a hospital.

Also, consult your doctor or pharmacist if you are using this medicine in combination with medicines. Depending on the ingredients in the supplement, the side effects of the medicine may be stronger or the effects may be weakened.

[Source] “Correct usage of health foods” (Ministry of Health, Labor and Welfare)
https://www.mhlw.go.jp/topics/bukyoku/iyaku/syoku-anzen/dl/kenkou_shokuhin00.pdf

Keep your body healthy even in winter by taking vitamin D

In this article, we mainly explained why you should actively take vitamin D in winter. Vitamin D deficiency is more likely in winter due to shorter daylight hours and fewer opportunities to go outside.

Vitamin D is an important nutrient that supports daily health. Try to overcome your vitamin D deficiency by getting outside and eating foods rich in vitamin D.

Also, if you are concerned about vitamin D deficiency, one option is to use supplements. With "Lypo-C Vitamin C+D", you can take in 1000mg of vitamin C and 2,000IU (50μg) of vitamin D in one package. Please use it to maintain your daily health.

Article supervision

Director Yu Hasegawa
You's clinic Aoyama

After graduating from Juntendo University School of Medicine and Graduate School, he joined the Department of Plastic Surgery and Radiology at Juntendo Hospital.
After working at a beauty clinic in Tokyo, she became the director of multiple clinics.
You's clinic Aoyama opened in March 2021.
She deals with beauty and health every day while working closely with patients in a private space.

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