Scientists from Mass General Brigham looked at whether vitamin D could help people who get COVID‑19. They gave a big group of adults a high dose of vitamin D3 or a fake pill (placebo) for four weeks.
The trial, called VIVID, involved 1,747 people who had just tested positive for COVID‑19 and 277 of their family members. Participants started the pills about three days after their test result. The dose was 9,600 IU per day for the first two days, then 3,200 IU each day after that.
Researchers checked if the vitamin D made the illness less serious or stopped the virus from spreading to household contacts. They found no big difference. Hospital visits, clinic appointments, and symptom severity were about the same for the vitamin D group and the placebo group.
However, when they looked at people who took the vitamin D every day as planned, they saw a small hint that it might help with long COVID. About 21% of the vitamin D group still had at least one lingering symptom after eight weeks, compared with 25% of the placebo group. This difference was just on the edge of being statistically important.
Long COVID can cause tiredness, trouble breathing, brain fog, and other problems that affect daily life. The researchers say more studies with larger groups are needed to see if ongoing vitamin D use can truly lower the risk or severity of long COVID.