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Why Do We Need Vitamin D?

By Rhianna Ross, RHN

What is Vitamin D?

Vitamin D, or the ‘sunshine vitamin,’ is a cholesterol-like, fat-soluble vitamin. Vitamin D is manufactured in our bodies when the sun’s ultraviolet light hits our skin and interacts with a form of cholesterol in our skin. From the skin, it makes its way to the liver and then the kidneys where it is converted to its most active form, vitamin D3 (calcitriol). We store vitamin D in our brain, bones, liver, skin, and spleen.

Besides sun exposure, we get some vitamin D through our diets.

Food Sources of Vitamin D

Foods that contain some vitamin D include:

  • Salmon
  • Cod liver oil
  • Herring
  • Sardines
  • Egg yolks
  • Liver
  • Foods fortified with vitamin D—may be fortified with either vitamin D2 or D3
  • Wild mushrooms and commercially grown mushrooms that have been exposed to UV light

Vitamin D2 (ergocalciferol) which is found in mushrooms and some fortified foods, does not increase vitamin D levels as well as vitamin D3.

Why is Vitamin D Important?

group of smiling kids

Healthy vitamin D levels are essential during pregnancy for both mom and baby. A deficiency during this important time of growth can increase the risk of pregnancy complications such as preterm birth, gestational diabetes, and preeclampsia. Deficiency can also hinder the development of the baby and has been associated with low birth weight and developmental delays.

Vitamin D is essential for bone health and teeth formation, because of its role in regulating calcium metabolism and bone calcification. Low vitamin D levels will still result in poor bone health even with healthy calcium levels. 

Vitamin D is also involved in muscle development, strength, and function.

Vitamin D plays a role in immune system health and balance. Vitamin D deficiency has been linked to an increased risk of both overactive immunity and autoimmune disorders, as well as low immunity and increased infections.

Vitamin D deficiency has been associated with poor sleep quality in both children and adults.

Brain health is also dependent on adequate vitamin D levels, with deficiency in early life hindering brain development, and for adults a deficiency has been linked to impaired cognition.

Scientists are still exploring additional roles and benefits vitamin D plays in our health. For example, vitamin D and its role in the increased survival rate after a cancer diagnosis.

Signs of Vitamin D Deficiency

Vitamin D deficiency can be hard to spot as many people will not have any symptoms.

Symptoms of vitamin D deficiency may include:

  • Increased instances of illness and infection such as cold and flus
  • Muscles pain and fatigue
  • Joint and bone pain
  • Developmental delays
  • Irritability

An untreated vitamin D deficiency can lead to rickets, which causes bone to not form properly, leaving them soft and weak.

Vitamin D deficiencies have also been linked to cardiovascular disease and autoimmune disease.

Who Needs Vitamin D Supplementation?

We get the bulk of our vitamin D through sun exposure and some through food. However, for many people these sources do not provide enough vitamin D to achieve optimal health.

A 2013 report from Health Canada found that one-third of Canadians had insufficient levels of vitamin D. It also stated that this number did rise to 40% during the winter months and that even in the summer, 25% of Canadians still had insufficient levels. 

Breastfed babies: While breastmilk is the best and healthiest option for babies, it is not a great source of vitamin D. Offering your baby a vitamin D supplement is important to ensure they are getting their needs met.

People who live in areas with less sun exposure: Northern countries, such as Canada, receive less sunlight. And even when the sun is out, the sun’s rays are weaker during the winter and will not be strong enough to trigger the creation of vitamin D in our skin.

Children and adults using steroids long term: Prolonged steroid use can lead to vitamin D deficiency.

Post-menopausal women: Post-menopausal women are at an increased risk of vitamin D deficiency as estrogen is involved in vitamin D metabolism.

Those living in long-term care homes or assisted living: Our ability to make vitamin D decreases with age. On top of that, care home residents often do not get much time in direct sun.

People with darker skin tones: Pigmentation in the skin reduces the amount of sunlight the skin can absorb, which hinders the production of vitamin D.


Overweight or obese individuals: While the mechanism is not totally understood, individuals who are overweight or obese are at a higher risk of vitamin D deficiency.

Vegans and vegetarians: Both vegans and vegetarians are at an increased risk of vitamin D deficiency because their diets do not include foods that naturally contain vitamin D such as fish.

Those living in areas with high pollution levels: Air pollution reduces the amount of UV rays that reach the earth and therefore our skin, reducing our vitamin D levels.

How to Choose a Vitamin D Supplement

A supplement is an excellent way to ensure you and your family are getting enough vitamin D.

When choosing a supplement, be sure to look at the form of the vitamin D and the non-medicinal ingredients.

Avoid vitamin D2, which is sourced from yeast fermentation. Like the D2 found in foods, D2 supplements do not raise vitamin D levels as well as D3.

D3 supplements are sourced from either sheep’s wool (lanolin) or lichen. If you are vegan, lichen will be the source you will want to opt for.

Vitamin D3 supplements should contain fat or be taken with fat-containing foods to help with absorption.

Daily Requirements and Dosage for Vitamin D

Health Canada recommends the following daily intake for Vitamin D:

  • Infants 0 to 12 months: 400 IU
  • Children 1 to 9 years: 600 IU
  • Children and Adults 9 to 70 years: 800 IU


cartoon image of Rhianna Ross

About the Author

Rhianna Ross, R.H.N., is a registered holistic nutritionist based in Vancouver, BC. Rhianna has more than a decade of experience in the natural health and wellness industry, and currently works at KidStar Nutrients, where she enjoys reviewing and analyzing the latest nutritional research papers, meta-analyses, and journal articles.

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