More than 80% of coronavirus patients in a Spanish hospital were deficient in vitamin D, compared to about 47% of healthy people with similar demographics.
Patients with lower levels of vitamin D weren't necessarily at higher risk for more severe illness, though, but other factors could be at play.
The findings build on past research suggesting vitamin D, which particularly benefits the immune and musculoskeletal systems, may support the body in fighting COVID-19.
Evidence continues to build that vitamin D may influence your risk for COVID-19 and severity of illness if you do fall ill.
One of the most recent studies on the topic, published today in the Journal of Clinical Endocrinology & Metabolism, found that 80% of coronavirus patients in a Spanish hospital were deficient in the sunshine vitamin.
The findings suggest identifying and treating COVID-19 patients with vitamin D deficiencies, particularly those who are at high risk for severe cases of COVID-19 like older folks, could help improve outcomes.
82.2% of hospitalized patients were vitamin D deficient, while only 47.2% of healthy people were
To conduct the study, researchers compared the vitamin D levels of 216 COVID-19 patients in the Hospital Universitario Marqués de Valdecilla with the levels of 197 healthy people who were similar in terms of demographics like age and sex.
The study authors also looked at whether the severity of illness of those hospitalized correlated with how high or low their vitamin D levels were.
Excluding coronavirus patients who were taking vitamin D supplements, the researchers found 82.2% of COVID-19 patients were deficient in vitamin D, compared to only 47.2% of people in the comparison group. In general, male COVID-19 patients' vitamin D levels were lower than women's.
The study authors also found coronavirus patients with lower vitamin D levels were more likely to have hypertension and heart disease, raised markers of inflammation, and longer hospital stays.
Interestingly, though, they didn't find a relationship between vitamin D deficiency and COVID-19 severity, with no significantly higher rates of ICU admission, ventilator use, or death among those who were especially low in vitamin D.
Also intriguing was that the 19 coronavirus patients who were taking vitamin D supplements had slightly less favorable outcomes, including more ICU admissions, than those who weren't on the pills.
However, that finding may be at least somewhat explained by the fact that people who may most need vitamin D supplementation, like older folks at risk for fractures, are also those at high risk for severe COVID-19. Six of those 19 had also taken corticosteroids or immunosuppressants in the prior three months, which could have influenced their COVID-19 severity.
The findings suggest "vitamin D treatment should be recommended in COVID-19 patients with low levels of vitamin D circulating in the blood since this approach might have beneficial effects in both the musculoskeletal and the immune system," study co-author José L. Hernández, of the University of Cantabria in Santander, Spain, said in a press release.
Vitamin D supports the immune system, but still isn't a cure or bulletproof defense mechanism for COVID-19
How vitamin D affects coronavirus risk and severity has been of interest to researchers and health professionals since the beginning of the pandemic.
An earlier October study of 76 COVID-19 patients, also in Spain, for instance, found that those who received a metabolized form of vitamin D3 that can quickly increase vitamin D levels were significantly less likely to need intensive care, and none of them died, Insider's Gabby Landsverk reported.
That's compared to the 26 patients who did not receive the supplement, 13 of whom were admitted to the ICU and two of whom died.
Another study done in Italy in August found that after 10 days of hospitalization, about half of the 42 patients with severe vitamin D deficiencies died, while only 5% of patients with sufficient vitamin D levels died.
Other research from around the world has found that higher levels of vitamin D correlate with more mild illnesses, and that countries that have high levels of vitamin D also tend to have lower death rates from COVID-19.
The link makes sense because vitamin D is known to strengthen the body's ability to fight off viruses, and can help quell cytokine storms, or when the immune system overreacts to a viral invasion — something that affects many patients with severe COVID-19, Business Insider's Susie Neilson previously reported.
But other variables could be play; for instance, people who live in crowded housing or work long hours indoors doing essential jobs are both less likely to get sufficient vitamin D from sunlight and more likely to be exposed to COVID-19.
Still, getting sufficient — though not too much — vitamin D, either through sunlight, supplementation, or certain foods like fatty fish, is important not just for its potential protection against the coronavirus, but for overall health.
Deficiencies are also linked to heart disease, diabetes, immune system disorders, certain types of cancers, and bone problems like osteoporosis.
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