Shedding light on Canada’s vitamin D levels as we approach the shortest day of the year

As winter’s chill tightens its grip, there is something else that tends to dip along with the temperatures—our vitamin D levels. Millions of Canadians are falling short of vitamin D levels, with teens and younger adults most affected.

Vitamin D: A gift from the sun

Vitamin D is often referred to as the “sunshine vitamin” since direct sunlight prompts our skin to produce this essential vitamin. Vitamin D is important for health and well-being, as it helps to ensure that our bones stay strong.

Vitamin D levels are assessed by measuring the serum concentration (or level) of 25-hydroxyvitamin D (25(OH)D), which is a form of vitamin D that circulates in the bloodstream. A person with a concentration of serum 25(OH)D below 30 nanomole per litre (nmol/L) is considered at risk of deficiency and is associated with an increased risk of poor bone health, while a concentration above 50 nmol/L is consistent with bone health in practically all individuals. Though more is not always better; a vitamin D concentration above 125 nmol/L may actually be associated with an increased risk of adverse events. A concentration of serum 25(OH)D of 40 nmol/L is the cut-off point used by Health Canada to evaluate adequacy of vitamin D levels in a population or group; a level below 40 nmol/L may reflect an inadequate intake of vitamin D.

Children and seniors least likely to have lower vitamin D levels

The Canadian Health Measures Survey (CHMS) collected blood samples from a nationally representative sample of 10,761 people from January 2016 to December 2019 to learn more about the overall heath of Canadians. Our analysis showed that approximately two-thirds (65%) of Canadians had vitamin D levels above 50 nmol/L and 4% had vitamin D levels above 125 nmol/L. Meanwhile, 10% of Canadians had vitamin D levels from 30 nmol/L to 40 nmol/L, and 8% had vitamin D levels below 30 nmol/L.

Vitamin D levels varied by age group. Only a small number of children aged 3 to 11 (3%) had vitamin D levels below 30 nmol/L compared with teens aged 12 to 19 (12%). Among adults, vitamin D levels below 30 nmol/L were most likely among young adults aged 20 to 39 (13%) compared with those aged 40 to 59 (6%) and older adults aged 60 to 79 (4%).

The higher levels of vitamin D among older adults may be linked to supplement use. Canada’s dietary guidelines recommend that people over the age of 50 take a daily supplement containing vitamin D.

The likelihood of vitamin D levels below 30 nmol/L doubles during the winter

Vitamin D can be obtained by consuming certain types of foods and supplements, but it is also the only nutrient that can be synthesized by the body when exposed to sunlight. Vitamin D is produced in our body when our skin is exposed to ultraviolet B (UVB) rays emitted by the sun. Exposure to UVB rays is reduced during Canadian winters as the days are shorter, the sun is less intense, and the cold forces us to either stay indoors or bundle up to stay warm when we do venture outside.

As a result, vitamin D concentration below 30 nmol/L among Canadians more than doubles during the winter months (13% for the period from November to March) compared with the rest of the year (5% for the period from April to October) which includes the sunny—and sadly, too short—Canadian summer.

Food can help boost vitamin D levels

A more in-depth look at the CHMS data showed that eating certain foods can help boost your vitamin D levels; highlights from the study are available in the infographic, "The scoop on Vitamin D: Sources for every season". 

For example, Canadian adults who ate fish at least once a week were less likely to have vitamin D levels below 30 nmol/L than those who ate no fish (6% versus 11%).

Canadian adults who drank one glass of milk a day were also less likely to have vitamin D levels below 30 nmol/L (6% versus 10%).

Don’t despair, vegans! Canadian adults who drank one or more fortified plant-based beverage a day were less likely to have vitamin D levels below 30 nmol/L than those who did not (5% versus 9%).

Canadian adults who took vitamin D supplements were nearly four times less likely to have vitamin D levels below 30 nmol/L than those who did not (3% versus 11%).

While Canadian winters may challenge our "sunshine vitamin" intake, a little creativity and consuming vitamin D from foods or a supplement every day can help us to ensure that we weather the season with our health intact.