Researchers studied vitamin D levels in nearly 18,000 patients in London during the early COVID-19 pandemic. They found that people with low vitamin D were more likely to test positive for COVID-19. The study showed that Black patients had the highest rates of vitamin D deficiency (25%), followed by Asian patients (21%), and White patients (17%). These findings suggest that maintaining healthy vitamin D levels might help protect against COVID-19, though more research is needed to confirm this connection.

The Quick Take

  • What they studied: Whether people with low vitamin D levels were more likely to catch COVID-19 and how vitamin D deficiency varied across different ethnic groups
  • Who participated: 17,619 patients (62% female) from St Thomas’ Hospital in London who had blood tests between January and June 2020. Of these, 485 patients tested positive for COVID-19. The group included people from different ethnic backgrounds: Black, Asian, and White patients
  • Key finding: People who tested positive for COVID-19 had lower vitamin D levels than those who didn’t get infected. About 61% of COVID-positive patients had either low or insufficient vitamin D levels, compared to lower rates in the general patient population
  • What it means for you: Getting enough vitamin D may help your immune system fight off infections like COVID-19. This is especially important for people from Black and Asian backgrounds, who showed higher rates of vitamin D deficiency. However, this study shows a connection, not proof that vitamin D prevents COVID-19, so talk to your doctor about your vitamin D levels

The Research Details

This was a cross-sectional study, which means researchers looked at a large group of people at one point in time and compared their vitamin D levels to see if there were patterns. They collected blood samples from nearly 18,000 patients at a London hospital between January and June 2020, before COVID-19 vaccines were available. Later, they checked which of these patients had tested positive for COVID-19 between March 2020 and January 2021.

The researchers measured vitamin D by looking at a specific form called 25-hydroxyvitamin D in the blood. They then compared vitamin D levels across different groups based on age, weight, sex, ethnicity, and whether someone had COVID-19. They also looked at other health information from the patients’ medical records.

This approach allowed them to see patterns in the data without actually giving people vitamin D supplements and watching what happened—that would require a different type of study called a randomized controlled trial.

This study design is useful because it can quickly show whether two things are connected (like vitamin D levels and COVID-19 infection) in a real-world population. By studying nearly 18,000 actual patients from a diverse city, the results are more likely to apply to different groups of people. The large sample size and diverse population make the findings more reliable than smaller studies

Strengths: This study included a very large number of patients (17,619), making the results more trustworthy. It also included people from different ethnic backgrounds, which helps show whether findings apply to everyone. The vitamin D measurements came from routine blood tests, so they were done consistently. Limitations: Because this is a cross-sectional study, it shows that low vitamin D and COVID-19 are connected, but it doesn’t prove that low vitamin D causes COVID-19. Other factors (like sun exposure, diet, or where people live) could explain the connection. The study only included patients from one hospital in London, so results might be different in other places

What the Results Show

The study found that vitamin D deficiency was common across all ethnic groups studied. Among Black patients, 25% had deficient vitamin D levels; among Asian patients, 21% were deficient; and among White patients, 17% were deficient. When researchers looked at people who tested positive for COVID-19, they found even lower vitamin D levels: 24% of COVID-positive patients were deficient and 37% had insufficient levels (meaning not quite deficient but still lower than ideal).

When comparing COVID-positive patients to the general population, the difference was clear. Among all patients tested, about 17-25% had deficient vitamin D depending on ethnicity. But among those who got COVID-19, 61% had either deficient or insufficient vitamin D levels. This suggests that people with lower vitamin D were more likely to test positive for the virus.

The study also found differences between men and women in some groups. Black and White patients showed different vitamin D levels between sexes, but Asian patients did not. Age and weight were also important factors—older age was most important for White patients who got COVID-19, while weight was most important for Black patients who got COVID-19.

The research showed that vitamin D deficiency patterns varied by ethnicity, with Black patients having the highest rates overall. Among the COVID-positive patients who were deficient in vitamin D, 38% were White (with a median age of 67.5 years) and 35% were Black (with a median age of 52 years). This suggests that vitamin D deficiency affected different age groups differently depending on ethnicity. The study also found that vitamin D levels were connected to other health factors like body weight and age, which are known to affect COVID-19 risk

This research adds to growing evidence that vitamin D may play a role in COVID-19 infection risk. Previous studies had suggested that vitamin D helps regulate the immune system, and some research hinted that deficiency might increase COVID-19 risk. This study is one of the larger ones to examine this question in a diverse, real-world patient population. It confirms earlier findings while also showing that the pattern holds true across different ethnic groups, though the rates of deficiency vary

This study has several important limitations. First, it only shows that low vitamin D and COVID-19 are connected—it doesn’t prove that low vitamin D causes COVID-19. Many other factors could explain why people with low vitamin D got COVID-19 more often, such as where they live, how much sun they get, their diet, or their access to healthcare. Second, the study only included patients from one hospital in London, so the results might be different in other cities or countries. Third, the study was done early in the pandemic before vaccines were available, so results might not apply to vaccinated populations. Finally, the researchers couldn’t control for all possible factors that might affect vitamin D levels or COVID-19 risk, like outdoor activity or dietary supplements people were taking

The Bottom Line

Based on this research, it’s reasonable to have your vitamin D levels checked, especially if you’re from a Black or Asian background, as these groups showed higher deficiency rates. If you’re deficient, talk to your doctor about getting more vitamin D through sunlight exposure, diet (foods like fatty fish, egg yolks, and fortified milk), or supplements. However, this study doesn’t prove that vitamin D supplements will prevent COVID-19, so don’t rely on vitamin D alone for protection. Continue following public health guidance for COVID-19 prevention. Confidence level: Moderate—the study shows a connection, but more research is needed to prove vitamin D prevents COVID-19

Everyone should care about vitamin D levels for overall health, but this research is especially relevant for people from Black and Asian backgrounds who showed higher deficiency rates. People over 65, those who spend little time in the sun, or those with limited sun exposure should also pay attention. People with certain medical conditions that affect nutrient absorption should definitely discuss vitamin D with their doctor. However, if you’re already vaccinated against COVID-19 and maintain good vitamin D levels, this study doesn’t change your current protection strategy

If you start taking vitamin D supplements or increasing sun exposure, it typically takes 4-8 weeks to see meaningful changes in blood vitamin D levels. However, any immune system benefits would likely take longer to develop. Don’t expect immediate protection from COVID-19 or other infections—building up your immune system is a gradual process

Want to Apply This Research?

  • Track your vitamin D supplementation (dose and frequency) and note any sun exposure time daily. Set a reminder to get your vitamin D levels checked every 3-6 months through your doctor, and log the results when you receive them
  • Start a daily habit of either taking a vitamin D supplement (if recommended by your doctor) or spending 10-30 minutes in midday sunlight several times per week. Log this activity in the app to build consistency and see patterns over time
  • Create a long-term tracking system that records your vitamin D supplementation or sun exposure habits weekly, your energy levels and immune health monthly, and your actual blood vitamin D test results when available. This helps you see whether your efforts are working and identifies seasonal patterns (vitamin D levels often drop in winter)

This research shows a connection between low vitamin D and COVID-19 infection but does not prove that vitamin D deficiency causes COVID-19. This article is for educational purposes only and should not replace professional medical advice. Do not start, stop, or change any supplements or medications without talking to your doctor first. If you have concerns about your vitamin D levels or COVID-19 risk, consult with a healthcare provider who can assess your individual situation. This study was conducted early in the pandemic before vaccines were widely available, so findings may not apply to current vaccination status or variants. Always follow current public health guidance for COVID-19 prevention