How vitamin D deficiency can lead to autoimmune diseases

As Canadians brace for the ‘vitamin D winter’ – months when the angle of the sun is too low to produce the vitamin in the skin – a study from McGill University explains why vitamin D deficiency is associated with early life with a higher risk of autoimmune diseases.

During childhood, the thymus helps train immune cells to distinguish between the body’s own tissues and harmful invaders. A vitamin D deficiency in that phase of life causes the thymus to age faster, the researchers discovered.

The study is published in the news Scientific progress.

“An aging thymus leads to a ‘leaky’ immune system,” says lead author John White, professor and chair of McGill’s Department of Physiology. “This means the thymus becomes less effective at filtering immune cells that might accidentally attack healthy tissues, increasing the risk of autoimmune diseases such as type 1 diabetes.”

He noted that researchers have known for years that vitamin D helps the body absorb calcium for strong bones, and that more recent research has discovered its crucial role in regulating the immune system.

“Our findings bring new clarity to this connection and may lead to new strategies for preventing autoimmune diseases,” he said.

Although the study was conducted in mice, the findings are relevant to human health because the thymus functions similarly in both species, White added.

The importance of a sunlight substitute

The findings highlight the importance of adequate vitamin D intake, especially for children.

“In places like Montreal, where we stop making the vitamin from sunlight between late fall and early spring, supplementation is critical,” says White. “If you have a young child, it’s important to check with your healthcare provider to make sure they’re getting enough.”

The breakthrough builds on a 2001 Finnish study in which more than 10,000 children were followed. This showed that children who received vitamin D at a young age had a five times lower risk of developing type 1 diabetes later in life.

Finland, with its long periods of vitamin D winter, served as an ideal case study for learning more about the nutrient’s many roles, White said.

In the McGill study, researchers used mice that could not produce vitamin D to investigate how the deficiency affected the thymus, using cell analysis and gene sequencing to see how this affects the immune system.

In future studies, White hopes to investigate how vitamin D affects the human thymus, something he says hasn’t been done before.