There are several ways to supplement Vitamin D. First, through diet, as foods like fish, egg yolks, and fortified milk are rich in Vitamin D. Second, by getting moderate sun exposure, as UV rays from the sun help the skin synthesize Vitamin D, but be careful not to stay in the sun too long. Finally, if diet and sunlight are insufficient, you can take Vitamin D supplements under a doctor's recommendation. Avoid excessive intake, as too much Vitamin D can lead to health issues.