What is Vitamin D?

May 1, 2015




Your body can make its own vitamin D from sunlight. You can also get vitamin D from supplements and a very small amount comes from a few foods you eat.


The vitamin D that you get in your skin from sunlight, and the vitamin D from supplements, has to be changed by your body a number of times before it can be used. Once it’s ready, your body uses it to manage the amount of calcium in your blood, bones and gut and to help cells all over your body to communicate properly.


What does vitamin D do?




The link between vitamin D and strong healthy bones was made many years ago when doctors realized that sunlight, which allows you to produce vitamin D, or taking cod liver oil, which contains vitamin D, helped to prevent a bone condition called rickets in children. Today, vitamin D is seen as a vital part of good health and it’s important not just for the health of your bones. Recent research is now showing that vitamin D may be important in preventing and treating a number of serious long term health problems.


Vitamin D isn’t like most other vitamins. Your body can make its own vitamin D when you expose your skin to sunlight. But your body can’t make other vitamins. You need to get other vitamins from the foods you eat. For example, you need to get vitamin C from fruits and vegetables.


Also what makes vitamin D unique compared to other vitamins, is that when  your body gets its vitamin D, it turns vitamin D into a hormone. This hormone is sometimes called “activated vitamin D” or “calcitriol.”


Getting the right amount of vitamin D doesn’t depend on the foods you eat. To get enough vitamin D you need to expose your skin to sunlight regularly and you may also need to take supplements. This makes getting the right amount a little more complex compared to other vitamins and minerals.


Vitamin D is very important for strong bones. Calcium and phosphorus are essential for developing the structure and strength of your bones, and you need vitamin D to absorb these minerals. Even if you eat foods that contain a lot of calcium and phosphorus, without enough vitamin D, you can’t absorb them into your body. Vitamin D is important for general good health, and researchers now are discovering that vitamin D may be important for many other reasons outside of good bone health. Some of the functions of the body that vitamin D helps with include:


  • Immune system, which helps you to fight infection

  • Muscle function

  • Cardiovascular function, for a healthy heart and circulation

  • Respiratory system –for healthy lungs and airways

  • Brain development

  • Anti-cancer effects


Doctors are still working to fully understand how vitamin D works within your body and how it affects your overall health.


If your body doesn’t get enough vitamin D to keep it healthy, this is called vitamin D deficiency. Severe vitamin D deficiency can sometimes cause a condition called rickets in children and a condition called osteomalacia in adults. Both of these conditions cause soft, thin, and brittle bones.


A lack of vitamin D has also been linked to some other conditions such as cancer, asthma, type-II diabetes, high blood pressure, depression, Alzheimer’s and autoimmune diseases like multiple sclerosis, Crohn’s and type-I diabetes.


Your body gets vitamin D mainly from sunlight, though very small amounts can also be found in a few foods. You can also get vitamin D by taking supplements.


How does Vitamin D work?



When your skin is exposed to the sun, it produces vitamin D and sends it to your liver. If you take supplements or eat foods that contain vitamin D, your gut also sends the vitamin D to your liver. From here, your liver changes it to a substance called 25(OH)D. When your doctor talks about your vitamin D levels, he means the amount of 25(OH)D you have in your blood.


This chemical is sent all over your body where different tissues, including your kidney, turn it into activated vitamin D. This activated vitamin D is now ready to perform its duties. From here, it gets a little complicated, but you can think of activated vitamin D working in two ways:


  • Manages calcium in your blood, bones and gut

  • Helps cells all over your body to communicate properly


As you can see, vitamin D goes a long way from its original form from the skin, supplement or food. But without vitamin D, your body can’t perform at its best.




Vitamin D, Third Edition by Feldman D, Pike JW, Adams JS. Elsevier Academic Press, 2011.

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