The D Vitamin

What it is and what it does

Vitamin D is a steroid hormone essential for many of our body’s vital functions. The first documented and most well known purpose of vitamin D is its role in maintaining bone health. It enables the absorption of calcium from the digestive tract to ensure the body has adequate reserves to build bone tissue. While vitamin D appears in a number of forms, the one that seems to be of most benefit is D3 (cholecalciferol).

Deficiency in vitamin D causes rickets in children, a condition that leads to bent bones due to inadequate bone mineralization. Many older Canadians are also at risk of bone-mineralization problems including osteomalacia and osteoporosis, both of which are associated with inadequate vitamin D.

Health Canada recommends that most Canadians require at least 600 IU per day of vitamin D to maintain bone health, while those over 70 years require a minimum of 800 IU/day. Over the past couple of decades, research has shown vitamin D to have an essential role in many aspects of our health. Most prominently, elevated vitamin D levels have been linked to decreased risk of breast cancer and colon cancer. In addition, supplemental vitamin D has been linked to decreased risk of auto-immune conditions such as rheumatoid arthritis, protection from mood disorders such as depression as well as increasing muscle strength.

Did You Know… 

… that one of the only natural, food-based sources of vitamin D is mushrooms? Just a few minutes of exposure to UV light can maximize their vitamin D production, just like in our skin. Leave your mushrooms gill-side up on your windowsill for an extra vitamin D boost. Portobello, oyster and shitake mushrooms tend to have the highest levels.

An important and underappreciated role of vitamin D, especially in the winter months, is its function in the immune system. A growing body of research shows that having enough vitamin D increases the germ-fighting action of some immune cell types, while increasing the immune cell population, which prepares the body for future infections.

Researchers in Japan found that when school children were supplemented with 1200 IU/day, they were two-times less likely to get the flu than un-supplemented kids.  Another study found that intake of 2000 IU/day prevented and reduced the severity of upper respiratory tract infections. This established, yet growing, body of research highlights the need for Canadians to ensure they obtain enough vitamin D to optimize their body’s functioning.

Where we get it from

Vitamin D is often called the “sunshine” vitamin due to its production in the skin when exposed to sunlight.  A precursor molecule is “initiated” by UV-B rays to “pre-vitamin D,” which then moves into the blood where it is further “activated” in the liver and kidney. In the summer months, vitamin D production is maximized after about 10 minutes of mid-day sun exposure.


However, between late October and March, the tilt of the Earth’s axis scatters UV-B rays through the atmosphere, meaning that there is no vitamin D produced in the skin of those of us living in the Northern Hemisphere. This, coupled with an indoor lifestyle, has resulted in Canadians having chronically low levels of vitamin D with some estimates suggesting that 70-97% of Canadians have insufficient levels.

Because of its proven benefits in bone-health, the government has mandated fortification with vitamin D of some foods such as milk and milk alternatives. Natural, unfortified foods are rare and low in vitamin D, with the exception of certain mushroom species (see sidebar). An excellent, safe and cost-effective way to ensure you have optimal vitamin D levels is to consume a vitamin D supplement daily, particularly during the winter months. There are many products available at different dosages and different forms including tablets, capsules, or liquid drops.

Tips for Shopping

When selecting a vitamin D supplement, make sure it comes in the “vitamin D3” form. This form, called “cholecalciferol” is the active form in the body. Some products are sold in the plant-based “vitamin D2” form, which has been shown to be much less active in the body.

Research shows that health benefits are more pronounced when daily doses are taken rather than infrequent “bolus” doses. Consider taking a supplement that provides a single lower-dose every day rather than once a week.

Frequently Asked Questions

How do I know if I need more vitamin D? Is there a test?

Your health care practitioner can do blood test to assess your circulating vitamin D levels and provide guidance on what dose might be right for you. There may be an added cost to have this analysis done due to the growing popularity of vitamin D blood tests. As mentioned above, it is estimated that most Canadians have insufficient levels of vitamin D, and may benefit from a supplement at Health Canada’s recommended intake level.

Should I take a vitamin D supplement with food?

Vitamin D is a fat-soluble vitamin. This means that it should be taken with some form of fat or oil to be best absorbed in the digestive tract. Taking it with food or at the same time as an Omega-3 supplement can help to optimize absorption.

How much is too much vitamin D?

Health Canada has recently changed the upper limit of safe vitamin D intake from 2000 IU/day to 4000 IU/day. Because vitamin D is a “fat-soluble” vitamin, there is the risk that it can build up in tissues if very high doses are taken for a long period of time. Research is still exploring what the optimal levels of intake should be.

Is supplemental vitamin D safe for me and my family?

Consuming supplemental vitamin D is safe for all ages, when taken at the recommended dosage. In fact, even newborns should have a vitamin D supplement of 400 IU/d. Health Canada recommends the following levels for adequate vitamin D status: Babies/infants 0-12m: 400 IU/d Males/females 1y-70y: 600 IU/d Males/females 70y +: 800 IU/d

A final note

Consult with your health care practitioner regarding questions about any supplements you are taking. This document should not take the place of medical advice.