UVB Activation of AMPs Production in the Skin and the Innate Respiratory Immunity shows that we do need exposure to the UVB to maintain healthy immune system against COVID-19 and other respiratory infections. Vitamin D supplementation does not replace sunlight. Moderate exposure to sunlight is beneficial, not harmful. The winter season brings with it deficit of sunlight exposure. Lockdowns make things worse.
Currently, African-Americans in the northern states are in the worst situation. Most of them get only a small fraction of the necessary UVB exposure. Brown-skinned people in the north and Blacks in the south fare slightly better.
Dark skinned Indians-vegetarians is another high risk group, because they do not eat fish. Diet rich in fatty fish or cod liver oil (as was made in 1930’s), have been shown to improve respiratory immunity. Fish and fish oil contains vitamin D and fatty acids, which might have a synergetic effect.
White (skin types I-IV) people need less UVB light than darker skin types. Nevertheless, the deficit still occurs in winter. The face is responsible for most occasional UVB exposure in the north USA in winter. Wearing masks outdoor further decreases the exposure and increases the deficit.