I’m sure you are familiar with the saying, “make sure you drink your milk so you can grow up big and strong” or “drink your milk, it will give you strong bones”. I bet you’ve heard your parents, and almost definitely your grandmother, uttered this saying to you at least once throughout your life. Not to discount grandma, but what if I told you that an underappreciated vitamin added to the milk could be the reason you turned out to be as mighty as you are today?
That vitamin is vitamin D.
Vitamin D insufficiency affects almost 50% of the global population, and is of concern for Canadians due to our northern latitude. It is mandatory that milk in Canada is fortified with vitamin D so that 1 cup (250 mL) provides 100 IU. Our government is adding it to food because most people simply aren’t getting enough and the negative health consequences of insufficiency and deficiency are far reaching.
Vitamin D was initially discovered for its ability to cure rickets, a condition that causes weak bones and muscles in children. Often referred to as the “sunshine vitamin” (more on this soon), it is termed ‘D’ because it was the fourth in the sequence of vitamins discovered. When vitamin D levels are sufficient within the body, it can increase calcium levels 30-40%, hence its importance in the development and maintenance of strong bones, muscles and teeth.
In addition, vitamin D has a variety of other roles in the body, such as protecting against the risk of cardiovascular disease and colorectal cancer, and regulating the immune system with potential implications for type I diabetes and MS. Virtually every cell in your body can use vitamin D. It influences approximately 200 genes that help to contribute to your overall health.
Sources of this Mighty Vity
Most the vitamin D our bodies rely on is produced when our skin is exposed to sunlight. When sunlight reacts with cholesterol in our skin, a precursor form of vitamin D is produced that our liver and kidneys convert to its usable form. Vitamin D produced in the skin may last at least twice as long in the blood compared with ingested vitamin D through food and supplementation.
In Canada, vitamin D from sunlight exposure can only be synthesized in your bare skin during the late spring, summer and early fall months, from around 10am – 2pm, when the UV index is above 3. There is no one size-fits-all guideline for the right amount of sun exposure and the amount of time necessary to make sufficient vitamin D depends on many factors including clothing coverage, use of sunscreen, skin pigmentation, and age. For example, wearing a sunscreen with a sun protection factor (SPF) of 30 reduces vitamin D synthesis in the skin by more than 95%!
Generally, casual sun exposure 5 – 15 minutes around midday, several times a week, without the use of sunscreen during the appropriate time of year is thought to be enough to produce enough vitamin D, and is less than the time required for your skin to redden and burn. As you can see, conditions must be right for your natural vitamin D production to kick into gear.
Obtaining sufficient vitamin D from natural food sources alone is difficult. Vitamin D3 can be naturally found in several foods, including fatty fish (e.g. salmon, tuna, mackerel), fish liver oil, beef/pork liver, egg yolks, and some cheeses. Mushrooms are the primary source of vitamin D2, a precursor form to active vitamin D (D3). In Canada, certain foods are also fortified with vitamin D, including milk, margarine, and infant formula as well as some types of orange juice, yogurt, and breakfast cereals. Overall, the quantities of vitamin D present in food are small, and vitamin D obtained from diet alone is not enough to maintain adequate vitamin D status for most people.
Unless you are a sun worshipper in the summer months and consume large amounts of cod or beef liver frequently throughout the year, the best way to get additional vitamin D is through supplementation. Vitamin D is a fat-soluble vitamin so it is best taken with a meal that contains at least a mild amount of fat to help increase its absorption. However, it is important to be cautious with high doses of fat soluble vitamins long term because they can build up in the body over time and have the potential to cause toxicity.
In Canada, the upper tolerable limit of vitamin D is 4000 IU per day. In comparison, when an adult wearing a bathing suit is exposed to enough of the sun’s UV radiation that causes a slight pinkness to the skin 24 h after exposure, the amount of vitamin D produced is equivalent to ingesting between 10,000 and 25,000 IU.
Who is at risk of deficiency?
· People with a naturally dark skin tone have natural sun protection and require at least three to five times longer exposure to make the same amount of vitamin D as a person with a lighter skin tone.
· People who don't expose their bare skin to the sun. If you're not keen for the great outdoors, overprotect from the sun with clothing, and/or use liberal amounts of sunscreen every time you are outside, your skin is probably not producing adequate amounts of vitamin D.
· Older folks. The ability of your skin to produce vitamin D from sun exposure declines with age.
· Obese individuals. Studies show an association of low vitamin D blood levels and body mass index (BMI) greater than 30.
· Individuals with certain diseases. Cystic fibrosis, Crohn’s disease, and celiac disease all negatively affect the absorption of vitamin D in the intestines. Kidney and liver disease decrease the activation of vitamin D within the body.
· Individuals taking certain medications
Testing Vitamin D Levels
Vitamin D status is measured using a simple laboratory blood test. The test results give you a number in units of nmol/L (nanomoles per litre); that number will fall into a range that will tell you whether you’re severely lacking (deficient), somewhat lacking (insufficient), or getting enough vitamin D (sufficient).
The signs and symptoms of vitamin D insufficiency and deficiency can include muscle weakness, pain, fatigue, a weakened immune system, and depression. These symptoms are vague and may or may not be caused from lack of vitamin D. This is where testing your vitamin D becomes particularly valuable to check if insufficiency or deficiency are contributing to the root cause of what you are experiencing.
Unfortunately, OHIP doesn't cover the cost of testing for most people, unless you have certain medical conditions. However, testing vitamin D status is very affordable so I regularly check if my patients’ blood levels are adequate. Achieving and maintaining optimal levels can make a big difference in your current and future state of health so it is important to have a conversation with your naturopathic doctor to make sure you’re getting enough vitamin D all year long.
 Rogers, D. (n.d.). How Can I Get All the Vitamin D That I Need? Retrieved from https://bcdairy.ca/nutritioneducation/articles/how-can-i-get-all-the-vitamin-d-that-i-need#:~:text=According%20to%20food%20law5,milk%20fortified%20with%20vitamin%20D
 Vitamin D Fact Sheet [Scholarly project]. (n.d.). In Multiple Sclerosis Society of Canada. Retrieved from https://mssociety.ca/library/document/38cuveX9sSrF0QEZ1DfOMUaBilKTyRJk/original.pdf
 Pilz, S., Zittermann, A., Trummer, C., Theiler-Schwetz, V., Lerchbaum, E., Keppel, M. H., ... & Pandis, M. (2019). Vitamin D testing and treatment: a narrative review of current evidence. Endocrine connections, 8(2), R27-R43.
 Holick, M. F., Binkley, N. C., Bischoff-Ferrari, H. A., Gordon, C. M., Hanley, D. A., Heaney, R. P., ... & Weaver, C. M. (2011). Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. The Journal of Clinical Endocrinology & Metabolism, 96(7), 1911-1930.