People with extremely low levels of vitamin D in their blood were not more likely to test positive for antibodies to the coronavirus, the data showed. The presence of antibodies -- cells made by the immune system -- suggests past infection.
Those with moderately low levels of the vitamin also did not have a higher risk for testing positive for coronavirus antibodies, the researchers said.
"We found no evidence for an independent association between low levels of vitamin D" and testing positive for COVID-19 antibodies, wrote researchers from Quest Diagnostics, a national chain of medical testing laboratories.
"These findings do not support the hypothesis that vitamin D plays a role in susceptibility to ... infection," they said.
Vitamin D is considered to be an important nutrient for immune health, according to the Harvard T.H. Chan School of Public Health.
Earlier studies have suggested that having low levels of the nutrient could indicate poor immune system health and raise the risk for severe COVID-19.
This risk is particularly acute in Black people, who historically have lower levels of vitamin D than those in other racial and ethnic groups, studies show.
Data indicate that Black people also are at increased risk for infection and severe COVID-19.
More than 40% of adults in the United States are considered to be deficient in vitamin D, including roughly 80% of Black people, according to the recent estimates.
For this study, the Quest Diagnostics researchers tested more than 18,000 adults ages 37 to 56 in the United States for coronavirus antibodies.
All 18,000 adults had available information on prepandemic blood vitamin D levels in their medical records, the researchers said.
About one in four had extremely low levels of the nutrient in the blood before the pandemic, while another 60% had moderately low levels.
Among the study participants, 900, or 5%, tested positive for antibodies suggesting past COVID-19 infection.
Participants with extremely low levels of vitamin D were 4% more likely to test positive for coronavirus antibodies.
Those with moderately low levels, however, actually were 7% less likely to test positive, the researchers said.
"Individuals [positive for COVID-19 antibodies] did have lower vitamin D levels than [negative] individuals, both before and during the pandemic," the researchers wrote.
"However, low levels of vitamin D were not associated with [positivity] after adjusting for" other factors, they said.