Vitamin D, which is expected to enhance immunity, is contained in many fish such as salmon (picture is image = PIXTA)
Since the spread of new coronavirus infection, interest in immunity has increased. What is useful in foods and food ingredients? Yogurt and natto are popular in Japan, but vitamin D is the most popular ingredient in the world. It is abundant in fish and is also synthesized in the body by sunlight. On the other hand, a huge amount of research results has been announced that the risk of diseases and infectious diseases increases when the amount is insufficient. I would like to refocus on Vitamin D, whose functions other than bone maintenance have not been known in Japan.
The number one vitamin D popular in the US supplement market
To protect yourself from infectious diseases, what can we do in our daily lives besides measures such as washing hands, gargle, wearing a mask, and reducing the chances of infection through heavy contact. What seems to be in the mind of many people is to “improve immunity”. Other than doing moderate exercise and adjusting your sleep rhythm, the only things you can do are to think about your dietary balance and eat foods that may help.
It is new to me that fermented foods such as natto and yogurt were sold out at supermarkets and other stores when the new corona began to spread. It seems that the information about the immunostimulatory action and infectious disease prevention test that was announced for some lactic acid bacteria, and the image that the fermented food itself seems to be good for the body, influenced it. On the other hand, the functionality of "vitamin D", which has been attracting attention as an essential vitamin for maintaining immunity in the world, was not well known in Japan. However, even in Japan, sales of supplements that allow easy intake of vitamin D have increased sharply, and some products have more than doubled their year-on-year sales.
``Vitamin D has been the focus of attention in the United States for its ability to boost immunity and has become the number one supplement purchased in 2019,'' said Global Nutrition Group CEO, who is a consultant in the health food industry in Japan and overseas. Takeda Takeshi.
Magnesium in the second place is a mineral that tends to be deficient in a normal diet, and many research results on the risk reduction of type 2 diabetes and cardiovascular disease have been published. The third place is the omega-3 fatty acid, a fish oil ingredient popular in the United States, where fish consumption is still low compared to Japan. It is an ingredient that is said to be useful for lowering triglyceride levels and improving cognitive function.
Regarding the reason why vitamin D, which is the main source of intake with fish along with Omega-3, became the leader, Mr. Takeda said, "Since 2005, the number of research reports on vitamin D in humans has increased rapidly and its importance is widely recognized. In response to the increase in the number of papers, the market size of vitamin D supplements has grown 10-fold from 2005 to 2010 and 20-fold in 2019." .. Vitamin D supplements are said to be on the shelves in the US, labeled as "supporting immunity" and "stress care."
While vitamin D supplements are not well known in Japan, the Consumer Affairs Agency warns that advertisements that are effective for the new corona can be seen on the web. Mr. Takeda said, "There is no research report that vitamin D is effective against the new coronavirus at this time, and it is natural that the product should not be described as having a preventive effect. However, for example, antiviral effect (described later) Since we have also released highly reliable evidence, we fear that excessive advertising will lead to a decline in the credit of ingredients that should be evaluated well.”
About 80% of Japanese are "Vitamin D deficient"
Let's review what kind of ingredient vitamin D is. Vitamin D is a fat-soluble (fat-soluble) vitamin that promotes absorption of calcium from the intestinal tract and maintains a strong bone. A deficiency causes rickets (children), osteomalacia (adults) and other weak and fragile bones. “It was once important to avoid deficiency, but in recent years, research has shown that even a slight deficiency increases the risk of various diseases other than bone. Large scale in Japan According to a survey, about 80% of people with a vitamin D blood concentration of less than 30 ng (nanogram, nano is one billionth)/ml reached about 80%, and adults and the elderly could be deficient in all age groups. "Okay," says Professor Tanaka Kiyoshi of the Faculty of Nutrition, Kobe Gakuin University, who studies vitamin D. (Graph)
In addition, deficiency is considered to be less than 20 ng/ml.
Why are many Japanese people prone to vitamin D deficiency?
Vitamin D is common in fish such as salmon and sardines, but few other foods can take sufficient amount. It is also contained in mushrooms, but its amount is less than that of fish, and its type is different from that of fish and its physiological activity is low (vitamin D in fish is D3, mushroom is D2).
On the other hand, since vitamin D is a very important component that works throughout the body, humans acquire the ability to synthesize from cholesterol (7-dehydrocholesterol) in the body by exposing the skin to ultraviolet rays (UV). “However, the intake of fish, which is a source of vitamin D, has decreased, and the habit of thoroughly implementing UV care to prevent sunburn has become widespread, and the vitamin D deficiency is becoming serious in Japan as well. In areas where UV radiation is weak, the country has taken steps to require milk to be fortified with vitamin D (Canada), and give vitamin D supplements to pregnant women and infants free of charge (UK).''
What risk does vitamin D deficiency increase?
First, the absorption of calcium, which is the basic function of vitamin D, goes wrong, causing problems with bones. "Vitamin D also has a role in stimulating muscle protein synthesis, so if the concentration remains low, the risk of fractures and flails increases," says Professor Tanaka. A 1-year follow-up study of blood vitamin D levels and fall risk in Japan (1393 women aged 75 years and older) found that blood vitamin D levels in the deficient region below 20 ng/ml were weakened, The risk of falls was 1.4 times higher than that of people with 25 ng/ml or more.
From prevention of infectious diseases to reduction of cancer risk
In addition, vitamin D is involved in the maintenance of systemic immunity, which is of great concern in the world following the outbreak of the new corona. "Since the receptors that receive vitamin D are present in many immune cells such as T cells and B cells, it is thought that the satisfaction of vitamin D is important for maintaining immune function," says Professor Tanaka. A variety of immune-related functions have been confirmed, such as allowing macrophages responsible for innate immunity to produce antibacterial substances, and preventing lung inflammation and damage caused by viral infection.
For viral infections, an integrated analysis of the results of 25 studies investigating whether intake of vitamin D lowers the risk of suffering from acute respiratory tract infections due to influenza etc., resulting in a 12% reduction in risk, There is a report that a 42% reduction in risk was seen especially in people with low blood vitamin D levels (graph).
The correlation between the new corona and vitamin D has not been clarified, but according to the global clinical trial registration database, as of the beginning of July, nearly 30 human trials are planned worldwide to confirm this. In addition, even if the correlation is not certain at the moment, there is a paper recommending that "take vitamin D as a supplement for prevention and increase blood vitamin D concentration above 40-60 ng/ml" for prevention. [Note 2]
In immunological diseases, there are many studies on vitamin D deficiency and cancer risk as well as infectious diseases.
For example, breast cancer, which is common among Japanese women, has an 82% lower risk of developing it in women with 60 ng/ml or more than in women with vitamin D blood levels below 20 ng/ml (deficiency). There is a US study that analyzed the data. [Note 3]
For colorectal cancer, data from 17 studies worldwide show that people in the right dose range of 35-40 ng/ml have a 27% lower risk of developing cancer than people in the deficiency range of less than 12 ng/ml. [Note 4]
The Ministry of Health, Labor and Welfare has increased the recommended daily intake of vitamin D for people over the age of 18 from 5.5 μg to 8.5 μg in the 2020 “Japanese Dietary Intake Standards” to prevent fractures. On the other hand, in the United States and Canada, the recommended amount of vitamin D set by the dietary intake standard is "15 μg per day for people under 70 years old, 20 μg for 71 years old and over", which is still quite different from the standard amount in Japan. .. This is also related to the fact that in the United States and Canada, the value does not consider vitamin D production in the skin due to sunlight. “First of all, while aiming to prevent various diseases while clearing the standard amount (8.5 μg) in Japan, we would like to aim for the same level (15 μg) as in the US,” Tanaka advises.
When supplementing with supplements, "it is recommended to start from 10 μg = 400 IU per day, 20-25 μg = 800-1000 IU per day" (Professor Tanaka). [Note 5]
I also want to keep in mind that it is generated in the body by ultraviolet rays. When the sun is strong, it is possible to produce more than the standard amount of vitamin D in a relatively short time. If you are worried about the effects of UV rays on skin aging, check the website of the National Institute for Environmental Studies for "time to make the required amount safely". For each residential area, you can see the guideline of "sunlight irradiation time required for synthesizing 10 µg of vitamin D without causing redness of the skin and causing stains".
For example, in Yokohama on a cloudy day in July, if you spend 31 minutes outdoors at 10 o'clock, you can produce 10 μg of vitamin D while suppressing skin damage caused by ultraviolet rays.
The nesting life that has continued since early spring will also cast a shadow on the production of vitamin D by ultraviolet rays. I would like to take a walk in the morning and evening when the ultraviolet rays are not strong and eat fish consciously to avoid vitamin D deficiency. If you find it difficult, use supplements to make up for it.
[Note 2] Nutrients. 2020 Apr2;12(4):988.
[Note 3] PLoS One. 2018; 13(6): e0199265.
[Note 4] J Natl Cancer Inst. 2019 Feb1;111(2):158-169.
[Note 5] 10 μg = 400 IU is the amount shown in the “Guideline for Prevention and Treatment of Osteoporosis” (Japan Osteoporosis Society). 20-25 μg=800-100 IU is the amount that has been reported overseas for bone fracture prevention effect. According to Professor Tanaka.
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