The researchers divided the participants (average age of 43; 54 women, 6 men) into 3 groups who took one of the following:

4,000 IU of vitamin D3 daily
8,000 IU of vitamin D3 daily
No intervention (the control)

At the end of the trial, the levels of complement component 3, complement component 4, and plasma vitamin D had increased (improved) in the 2 vitamin D groups and were higher (better) than in the control group. Also, in both vitamin D groups, fatigue symptoms decreased (improved) and were lower (better) than in the control group.

Can a vitamin D supplement reduce fatigue and disease activity in lupus? Original paper