Vitamin D Deficiency — A Common Problem in Korea

Vitamin D is a fat-soluble vitamin that the body produces when skin is exposed to sunlight. It plays a critical role in calcium absorption, bone health, immune function, and mood regulation. Deficiency is linked to osteoporosis, muscle weakness, frequent infections, and depression.

Korea has one of the higher rates of vitamin D deficiency among developed countries, with national health survey data consistently showing a majority of adults have insufficient levels. The main reasons are: predominantly indoor lifestyles (long working and study hours), cultural preference for fair, even skin tone leading to deliberate sun avoidance and heavy use of sunscreen and UV-protective clothing, and long winters with limited sunlight hours and lower UV intensity at Korea's latitude.

The problem is compounded by limited dietary sources. Very few foods are naturally rich in vitamin D — fatty fish (mackerel, salmon, saury), egg yolks, and fortified dairy products are the main sources. Most people cannot meet requirements through diet alone.

Blood testing (25-OH vitamin D) is the standard way to assess levels. Normal is considered 50–150 nmol/L; deficiency is below 30 nmol/L. Treatment depends on severity: mild deficiency may be corrected with daily supplements (1,000–2,000 IU), while severe deficiency may require weekly high-dose supplementation under medical supervision.

Safe sun exposure — 15–30 minutes of midday sun on arms and legs a few times a week, particularly outside the winter months — can help, though this is a genuine trade-off against skin cancer and cosmetic sun-avoidance preferences that many people are reluctant to change. Vitamin D supplementation is therefore a practical, widely recommended alternative in Korea.