Summarize:

As soon as sunlight hits your skin, it is absorbed into your skin cells. This triggers the production of vitamin D, which occur next in the liver and then the kidneys. Once it is in your body, vitamin D helps promote calcium absorption, helps with the remodeling and growth of bones, is involved with making your immune system function properly, and helps with cell regulation and cell growth. Vitamin D also prevents softening of the bones, brittle bones, and rickets in children. So many people assume they are not deficient, but in fact many of us are deficient. There are groups of people who are particularly at risk for vitamin D deficiency, though it is something everyone should be aware of. People who are more at risk include:  Elderly adults Infants  Those with darker-toned skin Those with limited to no exposure to the sun Anyone with conditions that limit fat absorption, such as inflammatory bowel disease (IBD) People with excess weight or who are obese Those who have undergone gastric bypass surgery There are some risks involved with both low and high levels of vitamin D. Low levels of vitamin D might increase the risk of pancreatic and colon cancer. Low levels are also associated with an increased risk of autoimmune diseases, pre-diabetes, Type 1 and Type 2 diabetes, multiple sclerosis, and high blood pressure. Having too much vitamin D can also cause health issues. It can cause weight loss, anorexia, and a dangerously high heart rate. There are a number of medications, such as Cerebyx and Luminal, that can decrease your vitamin D levels. If you are taking these, ask your doctor if you need to take supplements to increase your levels. Some medications decrease the absorption of the vitamin D in your body, which include Questran, Xenical, and Colestid. Ask your doctor about possible interactions with these medications. As a general rule, make sure you wait at least two hours after you take these medicines to take your vitamin D supplements.
Learn how it works. Recognize a deficiency. Know the risks. Talk to your doctor.