Your skin makes vitamin D when it gets sunlight. You can also get it from fatty fish, fortified dairy, and supplements. It helps your body absorb calcium and keeps bones strong. It also supports normal immune function.
Many people take it daily to keep their levels up, especially in winter or when they don't get much sun. Take your dose with a meal that contains fat. That helps your body use it.
Very high doses can cause toxicity and raise blood calcium too much. Use caution if you take thiazide diuretics, digoxin, corticosteroids, or certain antacids. A blood test can tell you your level before you start supplementation.