Approximately nine out of 10 Koreans lack vitamin D, according to data from Korean Health Promotion Institute (KHEPI).

And it has been like this for some time.

According to the Health Insurance Review and Assessment Service (HIRA) in 2016, there was a significant rise in patients seeking medical treatment for vitamin D deficiency between 2010 and 2014. The number of patients receiving medical treatment for insufficient vitamin D rose from approximately 3,000 to 30,000, a 10-fold increase. Furthermore, the most recent data spanning five years from 2017 to 2021 indicates that this trend persists. In 2021, the number of patients suffering from vitamin D deficiency experienced a surge of 187 percent compared to 2017.

However, this is not a normal concern in other countries, said some foreigners living in Korea. 

A foreign national from Colombia living in Seoul expressed concern about her recent medical check-up.

“I was informed that I have a vitamin D deficiency and was advised to start supplements,” said the Colombian woman in her late 20s. “I was told that if my vitamin D levels have not increased by my next medical check-up, I will have to start receiving injections.”

However, she also pointed out that the timing of her medical check-up could have possibly affected her Vitamin D deficiency diagnosis as her test was conducted during the winter season.

Vitamin D supplements could reduce mortality risk: study

However, vitamin D supplements could benefit older adults if they are taken with calcium, a Korean study showed.

The recently published study conducted by Korean researchers using data from HIRA also investigated the mortality outcomes associated with calcium supplementation with or without low-dose vitamin D. Consequently, it found that mortality risk associated with cardiovascular disease (CVD) was decreased in the CaD (calcium supplementation in combination with vitamin D) group when the daily vitamin D dose received was less than 1000 IU.

"Our findings confirm that combined calcium and vitamin D therapy can contribute to reducing the risk of mortality," said Professor Kim Kyoung-jin, lead author of the study, adding, "These findings are meaningful in the Korean population, which tends to be vitamin D deficient, and it may be beneficial to apply combined calcium and vitamin D therapy to vulnerable populations with vitamin D deficiency."

Furthermore, German researchers have shown that a daily intake of vitamin D supplements could reduce cancer mortality by up to 12 percent. In particular, the study revealed that daily intake for people 70 years and older benefited most from vitamin D3 therapy and the effect was most evident when vitamin D intake was started before the cancer diagnosis.

Is vitamin D deficiency overcalculated in Korea?

Vitamin D is involved in calcium absorption, making bones strong, affecting the immune system, reducing inflammation, and helping muscle growth. Vitamin D is usually synthesized naturally by ingesting it through food or supplements, or by receiving ultraviolet rays from outdoor activities.

Vitamin D2 is a form contained in plant foods and supplements, while vitamin D3 is a form synthesized in the skin by receiving ultraviolet rays or a form contained in animal foods. However, they cannot be accessed easily from the diet as there are few foods rich in vitamin D.

The reason behind these alarming figures might be nothing more than an overcalculation according to some physicians that claim that the threshold for vitamin D deficiency has been set too high by devising a blood level equivalent to the recommended daily allowance.

Speaking at a medical forum organized by the National Academy of Medicine of Korea, Professor Myung Seung-kwon of Family Medicine at the National Cancer Center Cancer explained the Korean landscape.

“Most studies have used recommended intakes as the basis for defining deficiency or insufficiency of a particular nutrient which has led to the misclassification of most people who are meeting their nutritional needs as deficient,” Myung said.

Accordingly, he advised against vitamin D screening and prescription of oral or injectable vitamin D in healthy individuals as recommended daily allowances (RDA) were created more than 80 years ago, based on intakes in the top 2.5 percent of the intake distribution of healthy people, with a lack of clinical and epidemiologic evidence.