@burcinc-- Try and get your vitamin D from food sources and from the sun first. If you are unable to do so, then you should supplement with vitamin D capsules or tablets.
Most of us don't get enough sunlight in winter and that's usually when our acne is worse. Vitamin D is a natural acne treatment. Vitamin D actives a type of white blood cell (macrophages) that attacks bacteria. When there is a lack of vitamin D, macrophages only cause inflammation, they are not able to destroy the bacteria that leads to acne.
If you have a vitamin D lamp, you can benefit from that in winter. Otherwise, try and eat a lot of fish and eggs. Fish like salmon, tuna, sardines and eggs are rich in vitamin D. If this is also not possible, take supplements.