Vitamin D Study Reveals Unexpected Clue About Long COVID Risk

A large clinical trial suggests that high-dose Vitamin D supplements do not reduce the severity of COVID-19, but they may have a potential role in lowering the risk of Long COVID. The findings come from research led by scientists at Mass General Brigham and were published in The Journal of Nutrition.
Researchers conducted the Vitamin D for COVID-19 (VIVID) Trial to better understand whether vitamin D supplementation could influence infection outcomes. Vitamin D is widely known for supporting immune function, but previous studies examining its role in COVID-19 have produced mixed results.
The trial involved 1,747 adults who had recently tested positive for COVID-19 and 277 of their household contacts. Participants were randomly assigned to receive either vitamin D3 supplements or a placebo for four weeks. The treatment group took high doses of Vitamin D3, starting with 9,600 IU per day for the first two days followed by 3,200 IU daily.
Results showed that vitamin D supplementation did not significantly reduce hospitalization rates, symptom severity, or healthcare visits related to COVID-19. It also did not lower the likelihood that household contacts would become infected.
However, researchers observed a potential signal suggesting vitamin D might influence long-term outcomes. Among participants who closely followed the supplementation regimen, about 21% reported lingering symptoms eight weeks after infection, compared with 25% in the placebo group. These symptoms included fatigue, shortness of breath, and cognitive issues commonly associated with long COVID.
Although the difference was only borderline statistically significant, scientists believe the results justify further investigation. Larger studies are needed to determine whether long-term vitamin D supplementation could help reduce the risk or severity of persistent symptoms following COVID-19 infection.
REFERENCE: Davaasambuu Ganmaa, Kaitlyn A Cook, Polyna Khudyakov, Dorjbal Enkhjargal, Tsolmon Bilegtsaikhan, Kenneth H Mayer, Allison Clar, Michael Rueschman, Raji Balasubramanian, Aditi Hazra, Howard D Sesso, Valerie E Stone, Patricia Copeland, Georgina Friedenberg, Douglas C Smith, Quanhong Lei, Todd Lee, Emily G McDonald, Tserenkhuu Enkhtsetseg, Erdenebaatar Sumiya, Yansanjav Narankhuu, Myagmarsuren Erdenetuya, Dalkh Tserendagva, Rikard Landberg, Niclas Roxhed, Susanne Rautiainen Lagerström, JoAnn E Manson. A Randomized Trial of Vitamin D Supplementation and COVID-19 Clinical Outcomes and Long COVID: The Vitamin D for COVID-19 Trial. The Journal of Nutrition, 2026; 101398 DOI: 10.1016/j.tjnut.2026.101398