Vitamin D deficiency: Who is at risk and how to keep levels up this winter

As winter weather settles in Canada, a “silent” health issue could be impacting many in the country.

With people spending more time indoors and getting less sun as days get shorter, there is an increased risk of your vitamin D levels dropping, experts warn.

Vitamin D is well-known for its role in keeping bones, teeth and muscles healthy by promoting the body’s absorption of calcium. It is also critical for the proper functioning of our immune system, which protects the body from viruses and bacteria.

But vitamin D deficiency is a “widespread” problem not only in Canada but across the world, said Dr. John White, chair of the department of physiology at McGill University.

And weather is a contributing factor, as vitamin D levels obtained through sunshine fluctuate throughout the year, he said.

According to the latest Statistics Canada report from 2015, in the winter, about 40 per cent of Canadians were below the appropriate cut-off of vitamin D levels needed for healthy bones — 50 nmol/L. In the summertime, 25 per cent of the population were below the cut-off.

Anyone under 30nmol/L is considered vitamin D deficient, according to StatCan.

Without a 25-hydroxy vitamin D blood test it’s difficult to know if your levels are insufficient as there are few warning signs or symptoms, said White.

“It’s very much a silent thing,” he said.

People can produce their own vitamin D when their skin is exposed to ultraviolet light (UV) from the sun.

But long sun exposure is not needed to generate sufficient levels of vitamin D, said White.

In fact, 20 to 30 minutes of sun exposure is good enough, he said.

“You don’t have to lie outside for four hours in a bathing suit to get enough vitamin D — it’s actually relatively limited exposure.”

But in Canada, where the days are short for much of the year, we often don’t get enough sun to produce as much vitamin D as we need, Osteoporosis Canada says.

Foods, such as egg yolks and fatty fish, are other natural sources of vitamin D.

In Canada, many common foods like milk, margarine and infant formula are also fortified with vitamin D.

However, White noted that “most Western diets tend to be insufficient in vitamin D,” which is why supplementation is needed.

Dr. Richard Kremer, a physician-scientist at the McGill University Health Centre (MUHC), estimated that the average person will not get more than 100 or 150 IU of vitamin D in their diet today.

“If you don’t get sunshine exposure, especially in the winter months, then you have to fill in the gap with supplements,” he said.

Healthy adults under age 50 should have 400-1,000 international units daily, according to Osteoporosis Canada, which recommends routine year-round supplementation.

A dose of 800-2000 IU is recommended for people at high risk of bone fractures and osteoporosis.

Meanwhile, Health Canada continues to recommend a daily vitamin D supplement of 400 IU and foods that contain vitamin D every day.

As aging leads to reduced dietary intake and the ability to synthesize vitamin D from the sun, older people are at higher risk of lower vitamin D levels.

People of colour are also at an increased risk because darker skin limits the production of vitamin D from the sun.

According to Health Canada, it takes longer for people with more melanin, which is the natural pigmentation that makes the skin darker, to produce vitamin D from the sun’s UV rays.

“For a given sun exposure, if you have the darkest type of skin, you will make about six-fold less vitamin D from a given UV exposure than someone with the lightest type of skin tone,” said White.

There are several downsides and risks of vitamin D deficiency, including bone weakness (osteoporosis) in adults and a similar bone deformity illness, called rickets, in children.

Children who are profoundly vitamin D deficient or have some genetic defect in the use of vitamin D are 100 per cent certain of developing rickets, said White.

In older adults, it can also lead to osteomalacia, which is bone softening, and myopathy, a disorder of muscles attached to the bones, said Kremer.

The elderly, as well as menopausal women, could suffer from low bone density as a result of low vitamin D levels.

While levels below 25nmol/L have severe health implications that can cause muscle pain and decreased muscle strength, anything below 75 nmol/L also means you are at higher risk of fractures or osteoporosis, said Kremer.

Meanwhile, overdosing and vitamin D toxicity is also a concern.

Too much vitamin D raises the level of calcium in your blood, which can cause nausea, vomiting, poor appetite, constipation, weakness and weight loss. Vitamin D toxicity can also lead to kidney problems and bone pain.