Vitamin D

By Viktoriya Zabigaylo & Dr. Orest Szczurko

Research has shown many benefits of vitamin D including bone and muscle health, immune function, cancer prevention, maintaining hormone balance, cardiovascular health, mood disorders, skin health and more1. It is a nutrient that can be obtained from the diet, but it is not naturally found in many foods and is present in low amounts. The easiest way to obtain vitamin D is through sun exposure or supplementation.

Food sources:

Food sources of vitamin D3 mostly include fatty fish, eggs, milk and some meats. Since it is found in few foods and the amounts are relatively low, some foods such as breakfast cereals, cow milk, plant based milks, and orange juice are fortified (vitamin D3 is added to them).

Good sources of vitamin D3 include:

  • cod liver oil (1 tbsp) – 1360 IU
  • salmon or rainbow trout (3 oz) – 550-650 IU
  • fortified milks (1 cup) – 100-150 IU
  • fortified cereals (1 serving) – 80 IU
  • 2 sardines – 45 IU
  • 1 egg – 45 IU
  • beef liver (3 oz) – 40 IU
  • tuna (3 oz) – 40 IU 2

Mushrooms can also provide a modest amount of vitamin D, however it is in the D2 form. A ½ cup can yield around 350 IU 2.

Sun exposure:

The process of vitamin D production begins in the skin. UVB rays reach the skin and are converted into cholecalciferol. This form of vitamin D3, along with any dietary D3 and D2, are all processed in the liver to make the biologically active form 25-OH-D3. The final step is in the kidneys which create calcitriol (1,25-OH2-D3) – the other biologically active form of vitamin D in the body – to carry out functions such as maintaining calcium balance.

In the summer months, 1000 IU of vitamin D can be produced by the body with at least 15 mins of sun exposure. The best time is in the late-morning to mid-afternoon hours, with bare skin exposed in at least 25% of the body surfaces (such as arms or legs)3. However, this depends on various factors which means some people may require more sun exposure to produce the same amount of vitamin D than others. For instance, the darker you are, the longer it takes to for the skin to produce vitamin D. This is also true of age – the skin of older individuals is less able to produce vitamin D. Also, living in northern locations including most parts of Canada means less sun exposure throughout the year, and sometimes even during the summer. Spending lots of time indoors such as working in the office or at home, and the use of sunscreen or long clothing also reduces overall sun exposure 1,2.


The 25-OH-D3 form of vitamin D is the most commonly tested on bloodwork. A deficiency is defined as levels under 25 nmol/L, but insufficiency is within the range of 25-75 nmol/L 4. The optimal level is above 75 nmol/L 5.

A deficiency may be caused by low sun exposure, low dietary or supplement intakes, impaired GI absorption (ex. IBD), or the kidneys cannot convert to the active form (ex. kidney disease)2. Vitamin D deficiency is the main cause of Rickets in children and osteomalacia in adults.

An insufficiency can cause low mood or depression, muscle aches and weakness, low back pain, loss of bone density (which can lead to osteoporosis and fractures), and more 6.

Low vitamin D levels are very common in Canadians, with over 50% of people being low during the summer, and as high as 75% during the winter 7.

Health Canada currently recommends the following minimum intakes of vitamin D per day:

  • Infants: 400 IU
  • Children: 600 IU
  • Adults: 600 IU
  • Elderly: 800 IU
  • Pregnancy & lactation: 600 IU 8

Individual needs can vary greatly depending on skin color, dietary intake, geographical location, time spent outdoors, season, etc. This means that many people may require a higher vitamin D intake than the RDA.

Supplementation is an easy way to maintain optimal levels, especially if bloodwork shows deficient or insufficient levels. One study showed that a daily intake of 800 IU of vitamin D3 in adults can bring about 50% of the population to the optimal level of 75 nmol/L. Therefore for many people, vitamin D is often required in higher doses than what is currently recommended 9. For the same reasons, it is also a good idea to supplement year round, including in the summer 1. It is important to first test your blood vitamin D levels with your doctor or naturopath to determine your baseline level, and again after supplementing to determine how much you should be taking daily.



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