Koreans have a high rate of vitamin D deficiency due to indoor living and sunscreen use. It is important to understand the importance of vitamin D and the health problems that can occur when it is deficient, and to ensure that you are getting enough vitamin D through sun exposure, food, and supplements.
Vitamins are essential nutrients that regulate metabolism and physiological functions in very small amounts. Vitamins are similar to hormones in that they regulate bodily functions in small amounts, but unlike hormones, which are synthesized by the body’s endocrine system, vitamins must be taken in externally. For this reason, we often hear about the importance of vitamins in our lives. Vitamin D is the only vitamin that is synthesized in the human body, but just because it“s synthesized doesn”t mean we can ignore it. Koreans have a higher rate of vitamin D deficiency than other countries due to their indoor lifestyle and busy schedules. A study on vitamin D deficiency in Koreans analyzed the association between demographic, residential, and health-related characteristics and 25(OH)D status, and found that only 34.2% of men and 22.4% of women were adequate, while most were deficient or insufficient, indicating that many people are not getting enough vitamin D. In this blog post, we’ll take a look at the forms of vitamin D, how it is synthesized and metabolized, how it affects calcium homeostasis, why our bodies need it, and why Koreans are deficient.
Vitamin D is a fat-soluble vitamin, and there are two forms that have important effects on the body. The first is vitamin D2 (ergocalciferol), which is found in yeast and plants, and the second is vitamin D3 (cholecalciferol), which is made in the body from 7-hydrocholesterol in skin cells with the help of UVB rays from sunlight. Of these, vitamin D3 plays an important role in the human body.
How is vitamin D3 produced in the body? Ultraviolet light from sunlight is divided into long UVA, medium UVB, and short UVC depending on its wavelength, and it’s the medium UVB (290 to 315 nm) that is needed to make vitamin D. First, 7-hydrocholesterol in skin cells is converted to pre-vitamin D3 (a precursor to vitamin D3) with the help of UV light from sunlight, and about 50% of this pre-vitamin D3 is converted to vitamin D3 by heat within two hours. The synthesized vitamin D3 is then stored in the body’s adipose tissue, and the stored vitamin D3 is synthesized by the liver and converted into a hormone precursor called 25-hydroxyvitamin D3. 25-Hydroxyvitamin D3 (25-OH D3) travels through the blood to the kidneys, where it is converted to the final active form, calcitriol (1,25-(OH)2 D3), which is transported to the tissues and cells where it is needed and acts as vitamin D.
Vitamin D contributes to wherever calcium is metabolized, which can either help or destroy our bones. Converted in the kidneys, calcitriol increases calcium absorption by promoting the formation of calbindin, a calcium-binding protein in intestinal cells. Increased serum calcium indirectly inhibits PTH-induced increases in bone resorption by lowering the concentration of the bone-destroying hormone, parathyroid hormone (PTH). In addition, when the body is hypocalcemic, vitamin D stimulates the secretion of parathyroid hormone, which promotes the conversion of 25-OH D3 to 1,25-(OH)2 D3 in the kidneys.
The 1,25-(OH)2 D3 then acts like a hormone to promote calcium absorption in the digestive tract, in the bones to elute and release bone-stored calcium into the blood along with parathyroid hormone, and in the kidneys to maintain calcium homeostasis by increasing calcium reabsorption. Because of these actions, it is not recommended to take vitamin D without calcium.
As mentioned above, vitamin D is an essential component of calcium metabolism, which is important for bone health, and a vitamin D deficiency can lead to many diseases. Deficiencies include diabetes, breast, prostate, lung, and colon cancer, osteoporosis, high blood pressure, skin diseases (psoriasis, eczema, melanoma, etc.), obesity, rickets, muscle pain, tooth decay, asthma, fatigue, autism, vision loss, hearing loss, insomnia, migraines, schizophrenia, depression, memory loss, and dementia. Vitamin D has also been shown to have a protective effect against cancer. Epidemiologic studies have shown that people living in areas with the least amount of natural sunlight have higher rates of colorectal cancer, and a 19-year follow-up study found that vitamin D and calcium deficiencies were associated with a higher risk of colorectal cancer. In addition, the fact that the amount of 1,25-(OH)2 D3 decreases with age also points to a link between vitamin D and cancer. Studies have also shown that 1,25-(OH)2 D3 inhibits the growth of several cancer cells and reduces the formation, growth, and metastasis of cancer in vivo.
Koreans are likely to be vitamin D deficient due to the fact that many people live indoors and use sunscreen. When looking at the differences in 25(OH)D concentrations by characteristics of the Korean study subjects, both men and women had higher concentrations in rural areas than in urban areas, and higher concentrations in traditional houses than in apartments. According to occupational reclassification and unemployment/economically inactive status codes, both men and women had the highest 25(OH)D concentrations in skilled agricultural and fishery workers, and the lowest 25(OH)D concentrations in the unemployed group, which includes managers and professionals, office workers, students, and housewives, suggesting that occupation type and lifestyle have a significant impact on 25(OH)D concentrations. The recommended daily allowance for vitamin D in Korea is about 400 IU, but there is a growing consensus among experts that the optimal intake should be much higher, with recommendations of 1000 IU for adults and 2000 to 5000 IU for those with deficiency problems. However, as with vitamin A, too much can have side effects. It can cause loss of appetite, vomiting, diarrhea, and can lead to hypercalcemia, so it should be taken in moderation.
In this article, we’ve learned about the synthesis and metabolism of vitamin D, why we need it, and how vitamin D deficiency is prevalent in Korea. Vitamin D is synthesized in the body, but its role is very important. In addition to getting outside and soaking up the sun, there are other ways to absorb vitamin D, such as eating vitamin D-rich foods such as eggs, blue fish, and mushrooms, or taking vitamin D supplements if needed. South Korea has a relatively high rate of vitamin D deficiency compared to other countries, so it’s important to be knowledgeable about vitamin D and try to maintain adequate levels in your body.
