Myung Seung-Kwon, Dean of Graduate School of International Cancer Graduate School, National Cancer Center
“Studies have also shown that high doses of nutritional supplements are harmful.
“A new definition is needed for the recommended daily intake of nutrients.”
According to the Health Insurance Review and Assessment Service, as of 2021, 73.7% of Koreans are vitamin D deficient. This means that 8 out of 10 people do not properly adhere to the recommended daily intake. Compared to 2017, the number of people with vitamin D deficiency increased by 186.3%. In particular, it was found that there were 3.5 times more women than men. It is known that not only Korea but also 68% of South Asians and 40% of Europeans are vitamin D deficient.
The recommended daily intake of vitamin D varies greatly from country to country. In the UK it is 400IU, the same as in Korea, but in the US and Canada, it is more, at 600IU. IU means International Unit. In the case of vitamin D, when converted to ㎍ (microgram, 1 ㎍ is 1 millionth of a gram), 1 IU is 0.025 ㎍. The recommended daily intake of vitamin D for Koreans is 10㎍.
Myung Seung-kwon, dean of the National Cancer Center International Cancer Center Graduate School (Professor of Family Medicine), said, “It has been known as if vitamin D deficiency is prevalent in Korea and around the world, but this is not true.” He added, “As vitamin D testing has become more and more popular, existing standards “It turns out that there are many people who do not fall under the criteria,” he said.
He said that because the recommended intake of vitamins itself was determined decades ago without a scientific basis, there is a need to redefine the definition and concept scientifically. Through this, we need to eliminate overconfidence in nutritional supplements and encourage people to consume nutrition through a balanced diet. On June 12, Director Myung published research results containing this claim in the international academic journal ‘Nutrition.’ On the 12th, we met with Director Myung at the National Cancer Center in Goyang-si, Gyeonggi-do, and conducted an interview.
What kind of nutrient is vitamin D?
“It is a fat-soluble vitamin and a type of hormone that influences the metabolism of calcium and phosphorus. If you lack vitamin D, your bones will become weak due to a lack of calcium and phosphorus. Vitamin D is found in large quantities in egg yolks and fish. Even if you are exposed to a lot of sunlight, ultraviolet rays stimulate the skin, and vitamin D synthesis occurs.”
It is said that 8 out of 10 Koreans are vitamin D deficient. Is that actually the case?
“If you consume 400 IU of vitamin D a day, the blood concentration is measured to be 20 ng/mL (nanogram, 1 ng is 1 billionth of a gram), and if you consume 600 IU, the blood concentration is measured to be around 30 ng/mL. Most healthy Koreans have a vitamin D blood concentration of about 12 to 20 ng/mL. The problem is that in most general hospitals and clinics in Korea, the standard for vitamin D blood concentration is 30 ng/mL, so most test takers are classified as deficient. This applies to more than 90% of women. “To meet the criteria, you need to take vitamin D supplements or take injections.”
Are there many people at risk due to a lack of vitamin D?
“Vitamin D deficiency weakens bones, increasing the risk of falls, fractures, and osteoporosis. But isn’t it true that most Koreans are suffering from these diseases? It is difficult to say that it is a vitamin D deficiency. Although specific research is needed, it is correct to consider the level of 12 to 20 ng/ml as normal. “It is not necessary to take vitamin D nutritional supplements, and rather, it is suspicious that the recommended daily intake of vitamin D is set at a much higher amount than it actually is.”
How was the recommended daily intake of vitamin D determined?
“In the 1940s, about 80 years ago, the decision was made solely based on the consensus of experts without any scientific basis. During World War II, nutritional deficiencies were very common. As many as 25% of American soldiers were malnourished. With insufficient clinical research, the U.S. National Academy of Sciences gathered the opinions of about 50 experts and established recommended intake amounts for each major nutrient, including vitamins. In other words, it can be said that the recommended intake amount was set without scientific basis and based on a standard that is too high compared to the amount actually needed by the body.”
Even if it was like that at first, you can correct it later, right?
“It’s still the same now. The current definition of recommended intake is ‘the average daily intake of a specific nutrient sufficient to meet the nutritional requirements of most healthy people (97.5%) in a specific age and gender group.’ Simply put, when 100 healthy people lined up in order of their intake of each nutrient, the amount consumed by the top 2.5% was set as the recommended intake amount. Because of this, most people are classified as deficient even though they have sufficient nutrients.”
Is the recommended intake amount for vitamin D only set that way?
“The recommended daily intake of vitamin C is the same. Korea and Japan have similar amounts of 100 mg (milligrams; 1 mg is 1/1000 of a gram) and France has 110 mg, but the United States has 90 mg, and the United Kingdom and India have 40 mg. The standards for nutrient intake differ greatly by nearly three times in each country. This is because countries that eat a lot of vegetables and fruits in their diet have the highest recommended intake. A person who consumes 41 mg of vitamin C per day in the UK becomes nutritionally deficient when he or she comes to Korea. “No matter how different the races are, the recommended intake of nutrients cannot be this different.”
How should the actual recommended intake amount be determined?
“Even 80 years ago, there were many people with nutritional deficiencies, so it may have been right to eat the recommended daily intake. But now is the time to eat well and live well. The concept and definition of the recommended intake amount that has been used so far must be changed based on scientific evidence. For example, rather than following the amount eaten by the top 2.5% of healthy people, follow the average amount of people. Taking vitamin D as an example, the blood concentration of the top 50% of healthy people is 16ng/mL. In 2018, researchers at the University of Missouri School of Medicine also published research results showing that the optimal blood concentration of vitamin D is 12 to 20 ng/mL in the international academic journal ‘Journal of the American Academy of Family Medicine.’ “Most healthy Koreans fit this figure.”
Then, we need to know the nutritional intake status of the people.
“Recently, a valid epidemiological research methodology has emerged to identify nutrient intake and optimal health status. It is a cohort study that investigates the incidence and mortality of diseases in a large group. Just as obesity can be determined based on body mass index (BMI, body weight divided by the square of height), the recommended intake of each nutrient must also be newly determined through cohort studies to determine the intake range that shows optimal health. The Ministry of Health and Welfare and the Korean Society of Nutrition establish and announce nutrient intake standards for Koreans every few years. At this time, the guidelines must be changed to suit the current situation, but the results of meta-analysis studies conducted over the past 10 years are not reflected.”
How about taking nutrients through nutritional supplements such as multivitamins?
“There is no clinical basis for the claim that vitamin supplement intake, especially high-dose therapy, is beneficial to health. Although there have been several positive results in animal and laboratory studies, it has not been proven in clinical studies on humans. Conversely, there are also research results showing that nutritional supplements are bad for health. Researchers at the University of Missouri School of Medicine analyzed 573 studies on vitamin D and found that vitamin D supplements did not prevent fractures, cancer, or cardiovascular disease. Rather, it was pointed out that excessive consumption can cause kidney stones, soft tissue calcification, etc. Researchers at Harvard Medical School and Brigham and Women’s Hospital also announced in the New England Journal of Medicine (NEJM) in 2022 that as a result of a study of 25,871 people, taking vitamin D supplements did not prevent fractures or osteoporosis in old age.”
I heard that similar results were obtained in Korea as in the United States.
“Our research team also conducted a meta-analysis of 15 studies published in international academic journals between 1992 and 2021 and found that high-dose vitamin D therapy was not effective in preventing fractures or falls. It was even revealed that vitamin D therapy actually increased the risk of falling by 6%. It was analyzed that administering high doses of vitamin D may actually reduce muscle function due to bone loss and muscle weakness due to hypercalcemia, a decrease in active vitamin D concentration, and a subsequent decrease in calcium utilization by muscle cells. In other words, there is no scientific evidence that supplementing nutritional supplements is good for the health of healthy people, other than surgical patients or patients with vitamin deficiency symptoms.”
Have similar research results been found for other nutritional supplements?
“There is still no scientific evidence that not only vitamins but also nutrients such as calcium, omega-3, probiotics (lactic acid bacteria), krill oil, and red ginseng are good for health. For example, our research team conducted a meta-analysis of 13 clinical studies published in international academic journals between 1990 and 2013 and found that taking calcium supplements actually increases the risk of cardiovascular disease by 15%.”
Then how should you consume nutrients?
“It is best to consume nutrients by eating a balanced diet and eating the right foods. Rather than artificially taking nutritional supplements, you should consume them naturally by eating enough foods rich in each nutrient. For example, eating blue-backed fish or mushrooms is sufficient for vitamin D. Additionally, since vitamin D is formed when exposed to sufficient sunlight, it is recommended to engage in outdoor activities for at least 10 minutes a day. Of course, regular aerobic exercise is also necessary.”
