At this time of year an ironic spotlight is cast on vitamin D. This nutrient is essential for a number of reasons, including its ability to prevent Seasonal Affective Disorder over the winter months, yet this is exactly the time when Canadians are least likely to get an adequate supply.
Vitamin D is important for immune function, building and maintaining strong bones, reducing inflammation, enhancing muscle function, reducing heart disease risk factors, and preventing diabetes, multiple sclerosis, and some cancers such as colorectal cancer.[i],[ii],[iii] Despite its importance, in Cycle 2 of the Canadian Health Measures Survey (CHMS; data collected between 2009 and 2011), 32% of Canadians were found to have blood concentrations of vitamin D below the cut-off level deemed sufficient for healthy bones for most people (50nmol/L).[iv] 59% of adults aged 20-39 years had blood concentrations below the cutoff.
The human body makes vitamin D upon direct exposure to sunlight. Unfortunately, during winter months (roughly November through May) in Canada, the sun is too far away to stimulate this process, resulting in a need to obtain this essential vitamin elsewhere. Additionally, the effectiveness of the sunlight conversion process declines with age. Biosynthesis also varies by skin tone and degree of exposure. Darker skin pigments require more sun exposure for effective development of vitamin D.[v] For all these reasons, vitamin D supplementation is recommended for all Canadians over the winter months.
How much vitamin D one needs depends on age and lifestyle. Breastfed infants require 400 International Units (IU) per day. In Canada, all infant formulas are fortified with vitamin D.[vi] Beyond infancy, the recommended intake for individuals aged 1-70 years is a combined daily intake from foods and supplements of 600 IU/day.[vii] This includes women who are pregnant or breastfeeding. Osteoporosis Canada recommends healthy adults aged 19-50 years (including pregnant and breastfeeding women) take 400 – 1000 IU/day, and those aged 50+ (or younger adults at high risk, such as those with osteoporosis) take 800 – 2000 IU/day.[viii]
Most foods are naturally low in vitamin D. Egg yolks and fatty fish such as salmon, mackerel, sardines, and tuna are the only foods that contain substantial amounts of naturally-occurring vitamin D.[ix] In Canada, fortification is mandated for infant formula, margarine, formulated liquid diets, cow’s milk and substitutes, egg products, foods used for very low energy diets, meal replacements, and nutritional supplements.[x] This low abundance of vitamin D in our food supply can make it tricky to get adequate amounts from foods alone in the winter.
While it is apparent that obtaining enough vitamin D is vital, it is important to note that this vitamin is fat-soluble, meaning it is stored in our body for long periods of time. Because of this, there is potential to consume too much of this vitamin. The Tolerable Upper Intake Level for vitamin D is 4,000 IU/day for males and females aged 9 and above.[xi] Consuming more than this amount on a regular basis can increase the risk of hypercalcemia,[xii] which can weaken bones, create kidney stones, and affect the heart and brain.
Nevertheless, given our less than optimal climate and our limited food sources, most adults will likely benefit from vitamin D supplementation. Supplements are sold as pills, chewable tablets, or liquid drops over the counter. A Registered Dietitian can help you decide what will be right for you to meet your daily vitamin D needs.
To increase your vitamin D intake, consider these suggestions:
Substitute milk or fortified plant based beverages for water in pancake, muffin, soup or smoothie recipes.
Make a yogurt parfait to enjoy as a make-ahead breakfast or snack on a daily basis.
Eat fatty fish, such as salmon, mackerel, sardines, or tuna, at least 2 times a week.
Click here to speak to a Dietitian more about vitamin D and your health.
[i] Osteoporosis Canada. (nd). Vitamin D. Retrieved December 27 2017 from https://osteoporosis.ca/bone-health-osteoporosis/calcium-and-vitamin-d/vitamin-d/
[ii] National Institutes of Health. (2016). Vitamin D. Retrieved December 28 2017 from https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
[iii] Dietitians of Canada. (2017). Vitamin D: What you need to know. Retrieved December 28 2017 from https://www.dietitians.ca/Your-Health/Nutrition-A-Z/Vitamins/Vitamin-D--What-you-need-to-know.aspx
[iv] Statistics Canada. (2015). Vitamin D blood levels of Canadians. Retrieved December 27 2017 from https://www.statcan.gc.ca/pub/82-624-x/2013001/article/11727-eng.htm
[v] Spector, T. D., & Levy, L. (2016). Should healthy people take a vitamin D supplement in winter months? BMJ, I6183. doi:10.1136/bmj.i6183
[vi] Osteoporosis Canada. (nd). Vitamin D. Retrieved December 27 2017 from https://osteoporosis.ca/bone-health-osteoporosis/calcium-and-vitamin-d/vitamin-d/
[vii] National Institutes of Health. (2016). Vitamin D. Retrieved December 28 2017 from https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
[viii] Osteoporosis Canada. (nd). Calcium and Vitamin D. Retrieved December 28 2017 from https://osteoporosis.ca/bone-health-osteoporosis/calcium-and-vitamin-d/
[ix] Dietitians of Canada. (2017). Vitamin D: What you need to know. Retrieved December 28 2017 from https://www.dietitians.ca/Your-Health/Nutrition-A-Z/Vitamins/Vitamin-D--What-you-need-to-know.aspx
[x] Osteoporosis Canada. (nd). Vitamin D. Retrieved December 27 2017 from https://osteoporosis.ca/bone-health-osteoporosis/calcium-and-vitamin-d/vitamin-d/
[xi] Government of Canada. (2010). Dietary Reference Intakes: Table 1 – Reference Values for Vitamins. Retrieved December 28 2017 from https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-vitamins-dietary-reference-intakes-tables-2005.html
[xii] Natural Medicines Comprehensive Database. (2017) Vitamin D Professional Monograph. Retrieved December 28 2017 from https://naturalmedicines.therapeuticresearch.com/databases/food,-herbs-supplements/professional.aspx?productid=929