Voluntary vitamin D testing: a decade-long study of utilisation patterns and impact on deficiency outcomes in Taiwan

Although guidelines recommend targeted vitamin D testing for high-risk populations, testing has increased globally. Limited studies have examined real-world testing patterns and their relationship with deficiency outcomes. This study investigates trends, demographic determinants and deficiency outcomes associated with voluntary vitamin D testing among Taiwanese adults.

A retrospective cohort study analysing electronic medical records to assess vitamin D testing trends, demographic predictors of deficiency and status changes following consecutive tests within 2 years. Vitamin D status was classified based on serum 25-hydroxyvitamin D levels as deficient (< 20 ng/ml), insufficient (20-29·9 ng/ml) or sufficient (≥ 30 ng/ml).

A tertiary medical centre in Taiwan.

Between 2013 and 2022, 13 381 outpatients underwent voluntary vitamin D testing. After excluding those aged < 18 years, with advanced renal disease, osteomalacia, rickets or hyperparathyroidism, 8383 were included in the final analysis.

Testing increased sharply after 2019. Although women underwent twice as many tests, men had a higher deficiency prevalence (56·94 % v. 53·01 %). Adults aged 18-34 years had the highest prevalence (67·81 %). Obstetrics and Gynecology specialists ordered the most tests, particularly for female infertility, with 65·73 % of patients deficient. Among those with repeat tests, deficiency prevalence decreased from 59.32 % to 43·25 %.

The increase in voluntary vitamin D testing with demographic disparities highlights the importance of understanding testing behaviours and public health implications. Improved vitamin D status at follow-up suggests potential benefits in identifying high-risk individuals and emphasises the need for further research to evaluate outcomes and guide prevention strategies.