Researchers in Taiwan looked at 10 years of medical records to understand who was getting vitamin D tests and whether testing helped people improve their vitamin D levels. They found that vitamin D testing became much more popular after 2019, especially among women and young adults. Interestingly, men were more likely to have low vitamin D even though women got tested more often. The good news: when people got retested after a year or two, their vitamin D levels improved significantly. This study shows that getting tested for vitamin D might help doctors identify people who need to boost their levels, but more research is needed to understand the full benefits.

The Quick Take

  • What they studied: How often people in Taiwan were getting vitamin D tests over a 10-year period and whether testing helped them improve their vitamin D levels
  • Who participated: 8,383 adults (18 years and older) who voluntarily got vitamin D tests at a major hospital in Taiwan between 2013 and 2022. The group included both men and women of various ages
  • Key finding: Testing for vitamin D became much more common after 2019. When people got tested again within two years, their vitamin D levels improved from 60% being deficient to only 43% being deficient—a meaningful improvement
  • What it means for you: If you’re concerned about vitamin D levels, getting tested may help you and your doctor identify a problem and make improvements. However, this study shows correlation (things happening together), not proof that testing itself causes improvement. Talk to your doctor about whether vitamin D testing makes sense for you

The Research Details

Researchers looked back at 10 years of medical records from a large hospital in Taiwan to track vitamin D testing patterns. They examined who was getting tested, how often testing occurred, and what their vitamin D levels were. They classified people into three groups: deficient (very low vitamin D), insufficient (somewhat low), or sufficient (healthy levels). For people who got tested more than once within two years, they compared whether their levels improved.

The study excluded people with certain medical conditions that would affect vitamin D levels, like advanced kidney disease or bone disorders. This helped ensure they were looking at typical people getting routine vitamin D checks. The researchers tracked trends over time to see if testing became more or less common in different years.

This type of study is valuable because it shows real-world testing patterns—what actually happens in doctor’s offices rather than in controlled experiments. Understanding who gets tested and whether testing leads to improvements helps doctors and public health officials make better decisions about vitamin D screening. It also reveals whether certain groups (like young adults or men) might be missing out on helpful testing

This study has several strengths: it includes a large number of people (over 8,000) and covers a long time period (10 years), which makes the findings more reliable. However, the study only looked at one hospital in Taiwan, so results might be different in other countries or regions. The study shows what happened but doesn’t prove that testing itself caused the improvements—people who got retested may have also made lifestyle changes or taken supplements. Additionally, the study couldn’t explain why testing increased so much after 2019 or whether all the improvements were due to medical interventions

What the Results Show

Vitamin D testing increased dramatically after 2019, suggesting growing awareness or changing medical practices. Women received about twice as many vitamin D tests as men, but surprisingly, men had higher rates of vitamin D deficiency (57% of men versus 53% of women). This suggests that men might not be getting tested as often as they should be.

Young adults aged 18-34 had the highest deficiency rates at 68%, meaning nearly 7 out of 10 young adults in this study had low vitamin D. Doctors specializing in women’s health (obstetrics and gynecology) ordered the most tests, particularly for women struggling with infertility—65% of these women had vitamin D deficiency.

The most encouraging finding: among people who got tested twice within two years, vitamin D deficiency dropped from 60% to 43%. This 17-percentage-point improvement suggests that identifying and addressing vitamin D deficiency through testing and follow-up care can lead to real improvements in people’s vitamin D status.

The study found that testing patterns varied significantly by age and gender. Older adults and men were underrepresented in the testing group, suggesting they may not be getting vitamin D checks as often as recommended. The concentration of testing in obstetrics and gynecology clinics indicates that vitamin D testing is being used particularly for fertility concerns, which aligns with research suggesting vitamin D plays a role in reproductive health. The sharp increase in testing after 2019 may reflect increased public awareness, media coverage, or changes in medical guidelines during that period

Previous research has shown that vitamin D deficiency is common worldwide, but few studies have examined real-world testing patterns in Asia. This study adds important information about how vitamin D testing is actually being used in clinical practice rather than how guidelines recommend it should be used. The finding that voluntary testing increased significantly aligns with global trends showing growing interest in vitamin D screening. However, the improvement in vitamin D levels at follow-up is consistent with other research showing that identifying and treating deficiency can be effective

This study only looked at one hospital in Taiwan, so the results may not apply to other countries or regions with different healthcare systems and populations. The study couldn’t determine why vitamin D levels improved—it could be from supplements, dietary changes, sun exposure, or medical treatment. We don’t know if people who got retested were more health-conscious overall, which could explain the improvements. The study also couldn’t explain the reasons behind the sharp increase in testing after 2019. Finally, the study excluded people with certain medical conditions, so results don’t apply to those populations

The Bottom Line

If you’re in a high-risk group (young adult, woman planning pregnancy, or have symptoms of vitamin D deficiency like fatigue or bone pain), ask your doctor about vitamin D testing. If you’re deficient, work with your doctor on a plan that might include supplements, dietary changes, or increased sun exposure. Retest after several months to see if your levels improve. For the general population without symptoms, discuss with your doctor whether routine testing makes sense for you based on your individual risk factors. (Moderate confidence—based on observational data showing improvement, not definitive proof)

Young adults (especially ages 18-34), women planning pregnancy or experiencing infertility, people with limited sun exposure, those with darker skin living in northern climates, and anyone with symptoms like bone pain, muscle weakness, or fatigue should pay attention to this research. People with kidney disease, bone disorders, or hyperparathyroidism should not use this information and should follow their doctor’s specific guidance. This research is less relevant for people living in sunny climates with regular outdoor exposure and no risk factors

If you start vitamin D supplementation or increase sun exposure, expect to see improvements in blood levels within 2-3 months. Most people in this study showed meaningful improvements within one to two years of follow-up testing. However, feeling better (reduced fatigue, improved mood, stronger bones) may take longer—typically 3-6 months or more depending on how deficient you were initially

Want to Apply This Research?

  • Log vitamin D test results when you get them (date and blood level in ng/mL). Set reminders to retest every 6-12 months if you’re deficient or insufficient. Track any supplements you take (dose and frequency) to correlate with test results
  • If your test shows deficiency, use the app to set a daily reminder to take vitamin D supplements or to spend 15-20 minutes in midday sun several times per week. Log dietary sources of vitamin D (fatty fish, fortified milk, egg yolks) to track intake. Set a goal to retest in 3 months to see if levels improve
  • Create a vitamin D status timeline in the app showing your test results over time. Compare your levels before and after making changes to see what works for you. Track symptoms like energy levels and mood alongside test results to see if improvements correlate. Share results with your doctor through the app if it has that feature to guide ongoing treatment decisions

This research describes patterns in vitamin D testing and improvements in vitamin D status, but it does not prove that testing itself causes health improvements. Vitamin D testing and supplementation decisions should be made with your healthcare provider based on your individual health status, risk factors, and medical history. This article is for educational purposes only and should not replace professional medical advice. If you have symptoms of vitamin D deficiency or concerns about your vitamin D levels, consult your doctor before starting supplements or making significant lifestyle changes. People with kidney disease, bone disorders, or other medical conditions should not self-treat based on this information.