Vitamin D is a nutrient your body needs for many important functions.

Vitamin D is a fat-soluble vitamin, meaning that it dissolves in fat and can be stored in the body longer than water-soluble vitamins.

It’s found in a few foods naturally, is added to some fortified foods, and can be taken as a supplement.

Vitamin D is known as the sunshine vitamin because it can be synthesized in the skin with UV rays from the sun.

Vitamin D has two main forms: D2 (ergocalciferol) and D3 (cholecalciferol).

While D2 and D3 are both well-absorbed in the gut, vitamin D3 raises vitamin D levels in the blood higher and keeps them there longer than vitamin D2 (3).

Vitamin D plays many roles and provides many benefits in the body.

Ongoing research is continuing to show new benefits of this vital vitamin. Vitamin D is strongly linked to bone health, immunity, and depression.

There are three ways to get vitamin D: from the sun, from foods, or from a supplement.

1. Your body makes vitamin D when your skin is exposed to UV rays from the sun. However, some people may have limited sun exposure, especially in some climates and seasons.
   
   You have to have direct exposure from the sun's rays, so being in front of a sunny window will not work.
   
   Plus, too much sun exposure can lead to skin cancer and aging skin. Rightly so, many people use sunscreen to protect their skin, but sunscreen blocks the skin’s ability to produce vitamin D.
   
   
2. Another way to get vitamin D is in your diet. While you should aim to get most of your nutrients from whole foods, it is very difficult to get enough vitamin D from diet alone.
   
   The few foods that naturally contain vitamin D are fish liver oil, fatty fish, such as trout, salmon, tuna, and mackerel, beef liver, cheese, egg yolks, and mushrooms.
   
   Most Americans get more vitamin D from fortified foods, such as vitamin D-fortified milk, breakfast cereals, and some orange juice and yogurt.
   
   Scientific data shows that 92% of men and more than 97% of women in the U.S. do not eat the recommended amounts of vitamin D (9).
   
   
3. If you don’t eat lots of fatty fish, don’t spend a lot of time in the sun, or use sunscreen to protect your skin, you should consider a vitamin D supplement.
   
   Remember that vitamin D3 is the best choice for a supplement.
   
   Ask your doctor to test the amount of vitamin D in your blood and if he/she recommends a vitamin D supplement for you.
   
   The only way to truly know if you have a vitamin D deficiency is to have a blood test that measures your vitamin D level.

Vitamin K is also a fat-soluble vitamin, and it is important for blood clotting, healthy bones, and healthy arteries.

The vitamin K family includes hydroquinone (vitamin K1) and several menaquinones (vitamin K2). Vitamin K1 is more important for blood clotting, and vitamin K2 is more important for bone health and preventing the calcification of arteries (10), (11).

Calcification of arteries means the buildup of calcium in the walls of the arteries which can lead to heart disease.

Vitamin K is found naturally in many foods, such as green leafy vegetables (spinach, kale, lettuce), broccoli, blueberries, eggs, meat, cheese, eggs, soybeans, and vegetable oils.

However, up to 31% of adults have insufficient levels of vitamin K, so a vitamin K supplement may be necessary (17).

Vitamin K can interact with the blood thinner, warfarin. If you take warfarin, make sure you get about the same amount of vitamin K every day, whether from foods or a supplement.

Many vitamins and other nutrients don’t work alone in your body and depend on each other.

Having a good intake of vitamin D and calcium can be dangerous if you don’t also get enough vitamin K.

Vitamin K helps get calcium into the bones.

If you are low in vitamin K, the calcium gets into your arteries instead of your bones, which contributes to heart disease. This leads to weak bones and hardened arteries.

If you and your doctor decide that you need to take a vitamin D supplement, make sure it also contains vitamin K2.

Because vitamin D and vitamin K are both fat-soluble, your supplement should be taken with a meal or snack that has some fat.

The fat in the food will help your body absorb the vitamins.