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The importance of vitamin D in winter


Did the winter blues get a hold of you? Perhaps you have a vitamin D deficiency. Vitamin D production is influenced by sunlight (UV rays), which transforms cholesterol in your skin into vitamin D3. Fortunately, there are several nutrients that replenish your vitamin D reserves.

Vitamin D

Why is vitamin D important?

Vitamin D combined with calcium is important for strong bones and teeth. This vitamin helps your body take in more calcium and prevents calcium from leaving your bones too soon. Vitamin D, then, is necessary during growth but also at an older age, to reduce the effects of bone loss (osteoporosis). In addition, vitamin D makes your muscles function better, optimizes your resistance and supports good brain functioning.

How much vitamin D do we need daily?

On average, an adult requires 10-15 µg (= 400-600 IU) of vitamin D per day. Overdoses (> 25 µg for children aged 0 to 10, > 50 µg for people over 11 years of age) may be dangerous. They can lead to hypercalcemia, neurological disorders and kidney stones. 

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Where can you find vitamin D?

Vitamin D occurs in two forms: vitamin D3, or animal-based cholecalciferol, and vitamin D2, or plant- or microbial-based ergocalciferol. The first type, vitamin D3, is mostly made in the skin under the influence of sunlight (UV rays). To a lesser extent, this vitamin is also found in food products: fish (e.g. herring, eel, mackerel, salmon), and, in smaller amounts, in egg yolk, dairy butter, whole dairy products and fatty meat. A lot of food products contain added vitamin D, such as butter, margarine, milk and cereal products. Sources of vitamin D2 include, among others, cabbage, oranges and wheat germ oil.

Vitamine D per portion

Recommended dietary allowances (% RDA)

1 piece of salmon (cooked, 125g)



1 piece of mackerel for 1 slice of bread (40 g)



Unsalted butter (for 1 slice of bread, 5g)



Margarine/low fat butter (for 1 slice of bread, 5g)



1 boiled egg (50g)



Vitamin D deficiency?

Most people don’t realize they don’t have enough vitamin D. Pain in your bones or weak muscles can point to a large vitamin D deficiency. In adults and elderly people, a vitamin D deficiency can lead to bone loss (osteoporosis) in the long term.

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Do you need supplements?

Vitamin D supplements are advised for

  • Children under 4 years of age
  • People with a dark skin color or bad skin pigmentation
  • People that don’t come into the sun during daytime or cover their skin
  • Pregnant women
  • Women older than 50
  • Men older than 70
  • Strict vegetarians
  • Vegans

If a vitamin D deficiency has already been diagnosed, it’s also a good idea to take supplements (not D2, but the more ‘active’ D3, cholecalciferol) at a dose of 600 IU per day. Vitamin D supplements exist as drops, ampoules or tablets and are available from the pharmacist without a prescription.

Practical tips

  • Make sure to keep your vitamin D status steady after you’ve supplemented the deficiency.
  • Try to go out in the sun for 15 to 30 minutes every day, with your hands and head bare.
  • During lunch break, go outside for a walk. This kills two birds in one stone: you get enough daily physical activity and you take up some vitamin D. Take your skin type into account. If you have very pale skin and the sun is shining very hard, it’s better to protect yourself than to go sunbathing. You shouldn’t get sunburned!
  • Try to eat more fatty fish, certainly in the winter.  

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