A large study adds to evidence that people with type O or Rh−negative blood may be at slightly lower risk from the new coronavirus.
Among 225,556 Canadians who were tested for the virus, the risk for a COVID-19 diagnosis was 12 percent lower and the risk for severe COVID-19 or death was 13 percent lower in people with blood group O versus those with A, AB, or B, researchers reported on Tuesday in Annals of Internal Medicine.
People in any blood group who were Rh-negative were also somewhat protected, especially if they had O-negative blood.
People in these blood type groups may have developed antibodies that can recognize some aspect of the new virus, coauthor Dr. Joel Ray of St. Michael's Hospital in Toronto told Reuters.
"Our next study will specifically look at such antibodies, and whether they explain the protective effect," Ray said. Whether or how this information might influence COVID-19 prevention or treatment is still unclear.
Low levels of vitamin D have been linked to higher risk for severe COVID-19, but high vitamin D levels do not fix the problem. Increasing vitamin D levels in critically ill patients did not shorten their hospital stay or lower their odds of being moved to intensive care, needing mechanical ventilation, or dying, doctors in Brazil found.
They randomly gave 240 patients hospitalized with severe COVID-19 either a single high dose of vitamin D3 or a placebo. Only 6.7 percent of patients in the vitamin D group had "deficient" levels of the nutrient, compared to 51.5 percent of patients in the placebo group, but there was no difference in the outcomes, according to a paper posted on medRxiv ahead of peer review.
The same was true when the researchers focused on the 116 patients with vitamin D deficiency before the treatment.
The authors say theirs is the first randomized trial of its kind to show that vitamin D supplementation "is ineffective to improve hospital length of stay or any other clinical outcomes among hospitalized patients with severe COVID-19."
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