Covid-19: vitamin D levels fell during pandemic

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The Covid-19 pandemic had effects on human health well beyond the infections themselves. A research team led by LMU epidemiologist Professor Eva Grill has demonstrated for the first time at the population level that vitamin D levels were significantly lower during the pandemic than before.

For their study, which was published in Nature Communications, the researchers analyzed anonymized routine data from 292,187 patients from all over Bavaria, covering both inpatients and outpatients. The data came from laboratory information systems which form part of a data-protection-compliant research platform.

The scientists compared laboratory values from the two years immediately prior to the pandemic (March 2018 to February 2020) and two years during the pandemic (March 2020 to February 2022). Their results show that the mean serum level of 25-hydroxy vitamin D fell from 26.7 µg/l to 26.0 µg/l over this period. At the same time, the proportion of people with vitamin D deficiency (below 20 µg/l) increased from 31.2 to 35.2 percent.

Significant decline in vitamin D values during pandemic

These differences were statistically significant (p < 0.001) and remained even after adjusting for age, gender, and season.

“A possible explanation is that lockdowns, home office working, and changed leisure habits reduced the exposure of many people to sunlight,” explains Grill.

To validate the results, the scientists employed three different statistical methods – classical descriptive analyses, propensity score matching, and machine learning. All methods independently confirmed the reduction in mean vitamin D levels and the increase in deficiency rates.

Elderly women, young adults, and urban dwellers particularly affected

Moreover, the evaluation revealed significant differences between population groups. Older women over the age of 60 were particularly affected by a decrease in vitamin D levels during the pandemic. Meanwhile, young adults aged 18 to 39 also exhibited a strong increase in vitamin D deficiency – their deficiency rate rose from 34.6 to 37.8 percent. Vitamin D is vitally important not only for bone health, but also has an immunomodulatory effect. Lack of the vitamin can increase the risk of infections, autoimmune diseases, and bone fractures.

In addition, there is an urban-rural divide: In urban regions, deficiency rates were consistently higher than in rural areas. “Urban living conditions – less sunlight as a result of building density, limited green areas, higher air pollution – further impair vitamin D synthesis,” notes Grill.

The researchers also interpreted their data against the background of gender-specific behavioral differences. While women on average take vitamin D supplements more often than men, they also experienced stronger falls in Vitamin D levels during the pandemic. According to Grill, this could be “an indicator that social and psychological factors like additional burdens, stress, and limited access to healthcare offers played a role for women.”

Routine data as a valuable instrument for public health research

As well as furnishing surprising insights, “our study shows that routine medical care data can be an early warning system for public health,” emphasizes Grill. “They allow us to quickly recognize trends such as the fall in certain nutrient levels or an increase in risk factors – without having to wait for time-consuming surveys.”

Grill also sees a way forward for health reporting in the design of the study. Through the integration of laboratory, invoicing, and healthcare data, it is possible to trace developments in things like micronutrients, metabolic parameters, and vaccination rates with little time lag – an important step toward data-driven prevention policy.

Lea Skapetze, Daniela Koller, Andreas Zwergal, Stefan Feuerriegel, Anna Rubinski & Eva Grill: Monitoring changes in vitamin D levels during the COVID-19 pandemic with routinely-collected laboratory data. Nature Communications (2025).

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