Vitamin D3 • Health Benefits and How to Prevent a Deficiency

donna braccia spalancate sorride al sole

Vitamin D3, Vitamin D, cholecalciferol or simply the sunshine vitamin: no matter what you call it, if you want to stay healthy and fit, this vitamin is one of the most important nutrients for your body. But what other benefits does the vitamin provide and how can you avoid developing a deficiency? 

Here we answer the following questions:

Ein Mann lacht und hält sein Gesicht in die Sonne

What is vitamin D? How does a vitamin D deficiency develop? 

In the fall and winter, when the days get shorter and the sun rarely peeks through the clouds, both our mood and our health take a downturn. You’ve probably heard of the “winter blues” or seasonal depression. One reason for this could be a vitamin D deficiency. 

Vitamin D has a special status among vitamins; your body can produce it from sunshine on your skin (UVB rays). In fact — surprise — vitamin D is actually a prohormone, or a substance that your body converts into a hormone, not a vitamin. You can also absorb vitamin D through the foods you eat, but you won’t get enough to prevent a vitamin D deficiency. 

The sunshine vitamin regulates the calcium and phosphate metabolism, which is why it’s important for bone structure. Furthermore, it is involved in a variety of metabolic processes in the body and can help build muscle strength. Vitamin D is mainly stored in muscle and fatty tissues; small quantities can also be found in the liver. 

Luckily, the overall storage capacity is relatively high and your body can draw on this during the winter. 

Good to know:

A vitamin D3 deficiency is not unusual in the northern hemisphere and places with long, dark winters. But some also develop vitamin D deficiencies in the summer, despite the fact that the sun is stronger. How can this be? When the temperature gets uncomfortably hot, a lot of people prefer to stay indoors in air conditioning, instead of leaving the house at midday.

The symptoms of vitamin D deficiency are very vague, which is why many people often fail to notice them. However, the following issues can indicate a vitamin D deficiency: 

  • Fatigue
  • Drop in performance
  • Insomnia
  • Susceptibility to infection
  • Muscle weakness
  • Wounds that heal poorly 
  • Dizziness 
  • Headaches

How much vitamin D do I need to be healthy?

A healthy vitamin D level is between 40 and 80 ng/ml. Have the vitamin D level in your blood checked by your doctor regularly (not only in the winter). This way you’ll be on the safe side and can address a deficiency early enough.

Ein Mann steht am Strand und hält ihr Gesicht in die Sonne

How can I make sure I get enough vitamin D?

  • Go outside in the sun (without sunblock) in the spring and summer three to four times a week for about 15 minutes to supply your body with this important vitamin. If you spend more than 15 minutes in the sun, it’s important to apply sunblock to protect your skin. 
  • The winter sun is too weak for your body to make sufficient vitamin D, but it can be stored. The vitamin D stores help keep your levels up throughout the wintertime.
  • Many people need to take supplements to prevent a deficiency in vitamin D. It’s important to have your doctor check the vitamin D level in your blood; the results of the blood test will help him or her decide which supplement makes sense for you. 

How are people treated for a vitamin D deficiency? 

If your doctor detects a deficiency in a blood test, he or she will give you a prescription for a high dose of vitamin D supplements for several weeks. This will refill your empty vitamin D stores. After this, your prescription will be lowered to a maintenance dose. The goal is to maintain a healthy level of vitamin D in your body.

What you should know:

This nutrient is a fat-soluble vitamin (along with vitamin A, E, and K). This means it can only be absorbed into your blood in combination with fat. That’s why you should always consume vitamin D supplements with some kind of dietary fat (cheese, nuts, avocado, high-quality vegetable oil). If you are taking vitamin D drops, you usually don’t need to worry about this, because the kind you get in the store is oil-based (usually coconut oil). Taking it with vitamin K is also beneficial.(1) Make sure that you are getting enough magnesium — this can help improve your vitamin D status, too.(2)

Vitamin D-reiche Lebensmittel und Supplemente

Which foods are rich in vitamin D?

If you want to boost your vitamin D absorption, include the following foods in your diet: 

  • Eggs: Hard boiled, in an omelet, or sunny side up: not only are eggs high in protein, they also have almost all the vitamins we need and are especially high in vitamin D.
  • Dairy products: Did you know that vitamin D boosts calcium absorption? If you include cow’s milk in your diet, you kill two birds with one stone.
  • Fish: Fatty fish (like herring) are a great source of vitamin D and essential omega 3 fatty acids. Tip: The WWF Sustainable Seafood Guide recommends which types of fish are healthy to eat and which you should avoid.
  • Mushrooms : Mushrooms, especially button mushrooms, are naturally high in vitamin D and thus a good option for vegans.

Did you know?

A vitamin D deficiency is very common and should be taken seriously. That’s why some countries (like Finland) offer foods like milk or butter fortified with vitamin D to reduce the large number of vitamin D deficiencies.(3)

What benefits does vitamin D have for my body?

  1. Important for bone health
    Vitamin D is extremely important to develop and strengthen your bones. The risk of bone fractures drops as the level in your blood rises. Vitamin D also reduces the risk of osteoporosis in old age. 
  2. Stronger muscles with vitamin D
    Studies have shown that vitamin D supplements can improve muscle strength. A meta analysis of eight studies published in Zurich in 2009 showed that the risk of falling was reduced by 19% in seniors who regularly took vitamin D supplements. The research results also indicated that competitive athletes who regularly took a combination of vitamin D and vitamin K experienced improved muscle strength and performance.  


Julia Denner Julia is a dietician and sports nutritionist. Before she began her position as Communications Specialist at Runtastic, she spent several years working as a dietician in the surgical department at Vienna General Hospital. Julia is passionate about inspiring others to eat a healthy, balanced diet. View all posts by Julia Denner