Researchers in Taiwan studied 481 people to see if vitamin D levels affected COVID-19 outcomes. While vitamin D didn’t seem to protect people from catching COVID-19, those with very low vitamin D levels who did get sick were much more likely to die from the infection. This was especially true for older adults. The findings suggest that maintaining healthy vitamin D levels might be important for survival if you do contract COVID-19, particularly as you age.

The Quick Take

  • What they studied: Whether people with different vitamin D levels had different chances of catching COVID-19 and whether vitamin D affected survival rates in those who got sick.
  • Who participated: 481 people in Taiwan (average age 58 years, about two-thirds were women) who had symptoms and got tested for COVID-19 between 2020 and 2023.
  • Key finding: Vitamin D levels didn’t affect whether people caught COVID-19, but people with very low vitamin D (less than 20 ng/mL) who got COVID-19 were about 10 times more likely to die from it compared to those with adequate levels.
  • What it means for you: If you have low vitamin D, it may not prevent you from getting COVID-19, but maintaining healthy vitamin D levels could be important for survival if you do get infected. This is especially important for people over 65.

The Research Details

This was a retrospective cohort study, which means researchers looked back at medical records from people who had already been tested for COVID-19. They collected information on 481 people who showed COVID-19 symptoms and got tested between 2020 and 2023. The researchers measured vitamin D levels in their blood and divided people into three groups: those with very low vitamin D (deficient), those with moderately low vitamin D (insufficient), and those with healthy levels (sufficient). They then looked at who got COVID-19 and who became seriously ill or died, while accounting for other factors that might affect outcomes like age, sex, and existing health conditions.

This study design is useful because it allowed researchers to examine real-world outcomes in a large group of people. By looking back at actual medical records rather than doing an experiment, they could see how vitamin D levels naturally related to COVID-19 outcomes. The researchers were careful to account for other factors that might explain differences, making the results more reliable.

The study included a reasonable number of participants (481 people) and carefully measured vitamin D levels using standard blood tests. The researchers adjusted their analysis for important factors like age and existing health conditions that could affect outcomes. However, because this was a retrospective study looking at past records, it can show associations but cannot prove that low vitamin D directly causes worse COVID-19 outcomes. The study was conducted in Taiwan, so results may not apply equally to all populations.

What the Results Show

Among the 481 participants, 96 people (about 20%) tested positive for COVID-19. When researchers looked at vitamin D levels and COVID-19 infection rates, they found no meaningful connection—people with low vitamin D were just as likely to catch COVID-19 as those with healthy levels. However, the picture changed dramatically when looking at death rates. Among those who got COVID-19, people with vitamin D deficiency (less than 20 ng/mL) had a significantly higher risk of dying. Specifically, they were about 10 times more likely to die compared to those with sufficient vitamin D levels. Age also played an important role: people aged 65-74 had about 13 times higher mortality risk compared to younger adults aged 19-44.

The study found that vitamin D insufficiency (moderately low levels) did not show the same strong association with death risk as severe deficiency did. This suggests there may be a threshold effect—very low vitamin D appears particularly dangerous, while moderately low levels may be less critical. The combination of advanced age and vitamin D deficiency appeared to create the highest risk group.

Previous research has suggested vitamin D plays a role in immune function and may influence COVID-19 outcomes. This study adds important nuance by showing that vitamin D’s protective effect appears most relevant for survival in those already infected, rather than for preventing infection in the first place. This aligns with emerging understanding that vitamin D supports immune response once infection occurs.

This study looked at people who already had symptoms and got tested, so it may not represent all people exposed to COVID-19. The number of people who died from COVID-19 was relatively small, which makes the statistical findings less certain. The study was conducted in Taiwan, and results may differ in other populations with different genetics, healthcare systems, or COVID-19 variants. Additionally, researchers couldn’t prove that low vitamin D directly caused worse outcomes—only that the two were associated.

The Bottom Line

Maintain adequate vitamin D levels (30 ng/mL or higher), especially if you are over 65 or have health conditions that increase COVID-19 risk. This can be done through sun exposure, food sources (fatty fish, fortified dairy), or supplements. If you have COVID-19 symptoms, ensure your vitamin D levels are checked. This recommendation is supported by this study but should be considered alongside other COVID-19 prevention strategies like vaccination.

This finding is most relevant for older adults (especially those 65+) and people with existing health conditions. Anyone concerned about COVID-19 severity should consider vitamin D status. However, this study does not suggest vitamin D prevents COVID-19 infection, so it should not replace vaccination or other prevention measures.

Vitamin D levels take several weeks to months to build up in your body through supplementation or increased sun exposure. If you’re concerned about COVID-19 risk, it’s worth checking your levels now rather than waiting until you’re sick. Benefits for immune function typically appear after 4-8 weeks of maintaining adequate levels.

Want to Apply This Research?

  • Track your vitamin D supplementation daily and record your serum vitamin D level (ng/mL) every 3 months through blood tests. Note any COVID-19 symptoms or infections and correlate with vitamin D levels over time.
  • Set a daily reminder to take a vitamin D supplement (if recommended by your doctor) and log it in the app. Record sun exposure time and dietary sources of vitamin D (fatty fish, fortified milk). Set a quarterly reminder to schedule vitamin D blood tests.
  • Create a long-term health dashboard showing vitamin D levels over time, COVID-19 exposure events, and symptom severity. Use this to identify personal patterns and maintain motivation for adequate vitamin D intake, especially during winter months or if you’re in a high-risk age group.

This research suggests an association between vitamin D deficiency and increased COVID-19 mortality risk, but does not prove that vitamin D deficiency directly causes worse outcomes. These findings are from a single study in Taiwan and may not apply equally to all populations. Vitamin D supplementation should not replace COVID-19 vaccination, medical treatment, or other proven prevention strategies. Before starting vitamin D supplements or making changes based on this research, consult with your healthcare provider, especially if you have existing health conditions or take medications. If you have COVID-19 symptoms, seek immediate medical attention rather than relying on vitamin D alone.