Vitamin D Supplements

Vitamin D is a fat-soluble vitamin that functions more like a hormone, regulating calcium absorption, immune defense, mood signaling, and over 200 gene expressions. Despite the body’s ability to synthesize vitamin D from sunlight, deficiency is widespread — studies suggest more than 70% of adults in Taiwan have insufficient levels, largely due to indoor lifestyles, sunscreen use, and air pollution blocking UV exposure.

Always choose vitamin D3 (cholecalciferol) over D2 (ergocalciferol), as D3 is significantly more effective at raising and maintaining blood levels of 25(OH)D. Pairing vitamin D3 with vitamin K2 (as MK-7) ensures that calcium absorbed under D’s influence gets properly directed to bones rather than soft tissues and blood vessels. Most adults benefit from 1,000–2,000 IU daily for maintenance; higher doses should be guided by blood test results.

Who is at highest risk of vitamin D deficiency? Indoor workers and those with limited sun exposure, people with darker skin tones (melanin reduces UV synthesis efficiency), adults over 65 (skin synthesis declines with age), obese individuals (vitamin D is sequestered in adipose tissue), vegans and vegetarians (few plant foods contain meaningful D3), and those who apply sunscreen consistently. Pregnant women and breastfed infants have elevated requirements that often necessitate supplementation.

An important safety consideration: vitamin D is fat-soluble and accumulates in the body — chronic supplementation above 4,000 IU/day can cause hypercalcemia if blood levels are not monitored. Ideally, supplement dosage should be calibrated to your baseline 25(OH)D blood level via routine testing rather than assuming a universal dose. This category covers the leading vitamin D3 brands with verified dosage, ingredient sourcing, and formulation details to help you choose appropriately.