What is vitamin D?

Vitamin D is a hormone your body produces when you come into contact with sunlight. It’s also a fat soluble vitamin found in food like fatty fish, eggs, and nutritional supplements. You need vitamin D for a handful of reasons including keeping your bones strong as it helps with the absorption of other essential nutrients like calcium and phosphorus — the building blocks of your bones. 

Vitamin D is also called the sunshine vitamin. When your skin comes into contact with the sun’s ultraviolet rays (UV rays), the receptors on your skin start synthesising vitamin D production. This makes it an easy nutrient to obtain if you live in a sunny place. If you don’t live in a sunny place, however, it is easy to become vitamin D deficient. 

The vitamin D is only naturally available in a few foods. You can get vitamin D from: 

  • Salmon
  • Mackerel
  • Tuna
  • Swordfish
  • Trout
  • Sardines
  • Fish liver oils
  • Beef liver
  • Egg yolks
  • Some kinds of mushrooms 

You can also buy vitamin D-fortified milks, breakfast cereals, and juices. 

How much vitamin D do you need? 

The amount of vitamin D a person needs depends on a couple factors. Vitamin D is measured in international units (IU). The amount of IU’s you need depends on: 

  • Your age
  • The climate you live in 
  • Your skin pigmentation  

Generally, children need between 400 and 600 IUs per day. An adequate daily intake for adults is 600-800 IUs. 

In addition to getting vitamin D through sunlight, it's easy to incorporate it into your diet. For example, just three ounces of rainbow trout contains almost 650 IUs, about 80% of what adults need daily. One tablespoon of cod liver oil contains a 1,360 IUs.

Skin pigmentation can determine how much vitamin D can be absorbed through your skin from natural sunlight. People who have darker skin tones have more melanin present in the skin. Melanin is a pigment that gives skin its color. Melanin acts like sunscreen and can prevent your body from converting the sun’s rays into vitamin D. 

Certain groups of people are at risk for vitamin D deficiency. You can develop a deficiency when you have a low vitamin D intake over a long period of time. 

At risk for a vitamin D deficiency include: 

  • People with limited sun exposure
  • Breastfed infants
  • People who follow a vegetarian or vegan diet
  • Older adults
  • People with certain medical conditions

Supplements can help you achieve your recommended daily intake. You can find vitamin D2 and D3 in most health food stores. Vitamin D3 is adapted from animal sources and is the kind of vitamin D that is naturally produced in the body. Vitamin D2 is made from plant-based sources and is what you will get from fortified foods. 

Eight benefits of vitamin D

Boosts your immune system 

Vitamin D can help boost your immune system and prevent the flu.

Helps prevent certain cancers 

Studies have shown that vitamin D can help prevent certain types of cancer and even slow tumor development. 

Helps prevent bone diseases 

People who get enough vitamin D and calcium in their diet are less likely to develop bone diseases like osteoporosis and osteomalacia. People who take calcium and vitamin D are also less likely to get bone fractures.

Helps prevent heart disease

Early studies show that vitamin D helps prevent heart disease by regulating your blood pressure and promoting healthy cell growth. 

Keeps your bones strong as you age

Because vitamin D is essential for bone health, you need to make sure you’re getting enough especially as you get older. Your bones can weaken over time, but a proper daily dose of vitamin D will help your body properly absorb calcium to keep your bones strong. 

Prevents painful muscle spasms and cramps

If you’re an athlete or regularly participate in sports, you’re probably aware of the sudden and painful onset of a muscle cramp. These cramps can be very intense and last for a few minutes. When vitamin D is absorbed in your gut alongside calcium and phosphorus, you are less likely to get these painful spasms. 

Reduces the risk of multiple sclerosis  

Multiple sclerosis (MS) is a degenerative nerve disease. Research shows that long-term vitamin D intake can reduce your risk of developing MS. Low vitamin D levels have also been associated with an increased risk of MS

Prevents mood disorders

When absorbed directly through the sunlight, vitamin D can help with Seasonal Affective Disorder (SAD). SAD affects people who live in places with low sunlight or who can’t leave their house. Researchers have also discovered a link between vitamin D deficiency and depression


Side effects of too much vitamin D

Use moderation 

Moderation is key when it comes to vitamin D. An adult should get about 600-800 IUs of vitamin D every day to enjoy its full benefits. Doses of more than 4,000 UIs per day can cause unwanted symptoms. 

Excessive vitamin D intake has also been associated with kidney stones. If you take too much, you can also experience:


Excessive amounts of vitamin D can be toxic. Although rare, studies show that doses higher than 4,000 UIs per day can result in:

Vitamin D consumption can also interfere with some medications. Consult your doctor if you think you’re not getting enough vitamin D or before adding any supplement to your diet. 


Vitamin D Deficiency: How Much Vitamin D Is Enough? See Slideshow

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Medically Reviewed on 3/23/2021

Harvard Health Publishing: "Taking too much vitamin D could cloud its benefits and create health risks."

Harvard T.H. Chan: "Vitamin D."

National Institutes of Health: "Vitamin D."