Researchers looked at blood test results from nearly 300,000 people in Germany to see if vitamin D levels dropped during COVID-19 lockdowns. They compared test results from before the pandemic (2018-2020) with results during lockdowns (2020-2022). They found that average vitamin D levels did drop slightly, and more people developed vitamin D deficiency. The biggest changes happened in older women. This study shows why it’s important to pay attention to vitamin D, especially when people spend less time outside.

The Quick Take

  • What they studied: Whether vitamin D levels in people’s blood changed during the COVID-19 pandemic when lockdowns kept people indoors
  • Who participated: Nearly 300,000 people in Bavaria, Germany who had routine blood tests done at a large laboratory. The group included people of different ages and genders
  • Key finding: Average vitamin D levels dropped from 26.7 to 26.0 units, and the percentage of people with vitamin D deficiency increased from 31% to 35%. These changes were statistically significant, meaning they weren’t due to chance
  • What it means for you: If you spent a lot of time indoors during lockdowns, your vitamin D levels may have dropped. This is especially important to know if you’re an older adult. Getting more sunlight and eating vitamin D-rich foods may help, but talk to your doctor about whether you need testing or supplements

The Research Details

Researchers used blood test results that were already collected by a large laboratory in Germany as part of routine medical care. They compared results from two time periods: before COVID (March 2018 to February 2020) and during COVID lockdowns (March 2020 to February 2022). This approach is called using ‘real-world data’ because it comes from actual medical practice rather than a controlled experiment.

To make sure they were comparing similar groups of people, researchers used special statistical methods. One method, called propensity score matching, helped them match people from the pre-pandemic period with similar people from the pandemic period. They also used another advanced method called causal forest analysis to understand which factors most affected vitamin D changes.

This type of study is valuable because it includes a huge number of people and reflects what actually happened in the real world, not just in a controlled lab setting.

Using real medical data from hundreds of thousands of people is powerful because it shows what actually happened to vitamin D levels during the pandemic, not just what researchers predicted might happen. The large number of participants makes the findings more reliable. The statistical methods used help ensure that the vitamin D changes were really caused by the pandemic and lockdowns, not by other factors like age or gender differences between groups

This study has several strengths: it includes nearly 300,000 people, which is a very large sample; it uses actual blood test results rather than surveys; it was published in Nature Communications, a highly respected scientific journal; and it uses multiple statistical approaches to verify the findings. However, the study only looked at people in one region of Germany, so results might be different in other countries. Also, researchers didn’t have information about individual behaviors like sun exposure or diet, so they couldn’t measure those directly

What the Results Show

The main finding was that vitamin D levels dropped during the COVID-19 pandemic. Before the pandemic, the average vitamin D level was 26.7 units per liter of blood. During the pandemic, it dropped to 26.0 units—a small but meaningful decrease. This might not sound like much, but when you look at the whole population, it meant that more people fell into the ‘deficient’ category.

The percentage of people with vitamin D deficiency increased from 31.2% before the pandemic to 35.2% during the pandemic. This means that about 4 out of every 100 additional people developed a vitamin D deficiency during lockdowns. The researchers confirmed this finding using three different statistical methods, which makes the result more trustworthy.

The decline was not the same for everyone. Older women showed the biggest drops in vitamin D levels and the largest increases in deficiency rates. This group may have been more affected because they might have spent even more time indoors during lockdowns or had other health factors that made them more vulnerable.

While the main focus was on overall vitamin D changes, the study also revealed important patterns by age and gender. Older adults, particularly women over 65, experienced more significant vitamin D declines than younger people. This is important because older adults already have higher risks of bone problems and falls, and vitamin D is crucial for bone health. The study also showed that the changes were consistent across the entire two-year pandemic period, not just at the beginning of lockdowns

Previous research had suggested that lockdowns might lower vitamin D levels because people spent less time in sunlight and might have changed their eating habits. This study confirms those concerns with real data from a large population. The findings align with what other researchers observed in different countries during the pandemic, suggesting this was a widespread issue, not just something that happened in Germany

The study only included people from Bavaria, Germany, so the results might be different in other countries with different climates or lockdown policies. The researchers couldn’t track individual behaviors like how much time people spent outside or what they ate, so they couldn’t measure these factors directly. The study also only looked at people who had blood tests done, which might not represent the entire population. Additionally, the study couldn’t determine whether the vitamin D changes actually caused health problems—it only showed that levels changed

The Bottom Line

If you spent extended time indoors during lockdowns, consider getting your vitamin D level checked with a blood test (moderate confidence). Spend more time outside in sunlight when possible, as this is the body’s main source of vitamin D (high confidence). Eat more vitamin D-rich foods like fatty fish, egg yolks, and fortified milk (high confidence). If your doctor finds you have low vitamin D, they may recommend supplements (high confidence when recommended by a doctor). This is especially important for older adults and people with limited sun exposure

This research is most relevant for older adults, especially women, who may have experienced the biggest vitamin D drops during lockdowns. Anyone who spent significant time indoors during the pandemic should consider getting tested. People living in northern climates with limited winter sunlight should also pay attention. People with conditions affecting bone health, immune function, or those taking medications that affect vitamin D should definitely discuss this with their doctor. This is less urgent for young, healthy people with regular sun exposure, but still worth monitoring

Vitamin D levels can change relatively quickly—within weeks of increased sun exposure or dietary changes. However, building up adequate vitamin D stores takes several weeks to months. If you start taking supplements or spending more time outside, you might see improvements in blood tests within 2-3 months. For bone health benefits, consistent vitamin D levels over months to years are important

Want to Apply This Research?

  • Track daily sun exposure time (in minutes) and vitamin D-rich food servings. Set a goal of 15-30 minutes of midday sun exposure most days and 1-2 servings of vitamin D-rich foods daily. Log these weekly to identify patterns
  • Use the app to set reminders for outdoor time during lunch breaks or morning walks. Create a simple checklist of vitamin D-rich foods to eat each week (salmon, fortified milk, egg yolks, mushrooms). If taking supplements, set daily reminders and track compliance
  • Log outdoor time and dietary vitamin D intake weekly. If possible, schedule annual blood tests to monitor vitamin D levels, especially during winter months or periods of reduced outdoor activity. Track any symptoms like fatigue or bone pain that might indicate deficiency. Share trends with your healthcare provider during annual checkups

This research shows an association between pandemic lockdowns and lower vitamin D levels but does not prove that low vitamin D caused specific health problems. Individual vitamin D needs vary based on age, skin tone, location, and health conditions. Before making changes to sun exposure, diet, or starting supplements, consult with your healthcare provider, especially if you have existing health conditions or take medications. This information is for educational purposes and should not replace professional medical advice. If you suspect you have a vitamin D deficiency, ask your doctor about blood testing and appropriate treatment options.