Vitamin D in Korea: Why Deficiency is So Common and How to Fix It

Vitamin D deficiency is one of the most prevalent nutritional deficiencies in Korea — studies have repeatedly found Korea among the countries with the highest rates of vitamin D deficiency in the world. The explanation is multifactorial: long working hours spent indoors in offices; a strong cultural preference for pale, sun-protected skin that leads to widespread use of sunscreen, parasols, and sun-protective clothing even in summer; and Korea's distinct winter season, when the sun angle is too low for efficient vitamin D synthesis for several months of the year.

Vitamin D plays critical roles in calcium absorption and bone health, immune function, muscle function, cardiovascular health, and mood regulation. Deficiency is defined as serum 25-hydroxyvitamin D (25-OH-D) below 50 nmol/L (20 ng/mL). Symptoms include fatigue, bone and muscle pain, low mood, impaired immune function, and — in children — rickets (soft bones). It has also been associated with increased risk of osteoporosis, autoimmune disease, and cardiovascular disease.

Testing involves a simple blood test (25-OH vitamin D level) available at local clinics and hospitals across Korea, and is often included in the NHIS national health screening. Supplementation is the mainstay of treatment — cholecalciferol (vitamin D3) is preferred over ergocalciferol (D2). Typical supplementation doses: 1,000–2,000 IU daily for maintenance; 50,000 IU weekly for 8–12 weeks (prescription strength) for correction of deficiency. Vitamin D supplements are widely available OTC at Korea pharmacies. Co-supplementation with vitamin K2 may improve vitamin D's effect on bone and cardiovascular health.