Which of the following best defines the threshold for vitamin D adequacy based on 25(OH)D levels?

• A. ≥ 50 ng/mL
• B. ≥ 30 ng/mL
• C. ≥ 20 ng/mL
• D. ≥ 10 ng/mL

Answer: (B)

The key idea is that the serum level of 25-hydroxyvitamin D reflects overall vitamin D stores and intake, making it the best measure of vitamin D status. Clinically, targeting a level of 30 ng/mL or higher (about 75 nmol/L) is considered adequate for most adults because this range supports optimal calcium absorption and helps keep parathyroid hormone in check, which protects bone health. While some guidelines define sufficiency as a lower threshold (around 20 ng/mL), many nutrition-support and endocrinology perspectives aim for 30 ng/mL to optimize outcomes. Levels well above this, such as around 50 ng/mL, are not routinely needed and can carry risks if sustained. Levels below 30 ng/mL indicate insufficient stores and prompt consideration of supplementation toward the 30 ng/mL goal.