Discovering a link between the sunshine vitamin and the immune response to cancer

A new study indicates a possible link between vitamin D and improving immunity, in an important breakthrough in the fight against cancer.

Vitamin D is primarily produced in the body after exposure to sunlight, but its levels can also be boosted by eating foods, such as eggs, oily fish and red meat.

The study conducted on mice found that the vitamin, known as the “sunshine vitamin,” encourages the growth of a type of gut bacteria, giving the animals better immunity against disease.

The researchers found that mice given a diet rich in vitamin D had better immune resistance to experimentally transplanted cancers, and their responses to immunotherapy improved.

The researchers were surprised to find that vitamin D acts on certain cells in the intestine, which in turn leads to an increase in the amount of bacteria called Bacteroides fragilis.

According to the results, the tumors did not grow as much, indicating that the bacteria gave the mice better immunity against cancer.

“What we showed here was a surprise,” said Caetano Reyes y Souza, head of the Immunobiology Laboratory at the Francis Crick Institute and senior author. “Vitamin D can regulate the gut microbiome to favor a type of bacteria that gives mice better immunity against cancer.” This may one day be important for treating cancer in humans, but we don't know how or why vitamin D has this effect via the microbiome. "More work is needed before we can definitively say that correcting vitamin D deficiency has benefits for preventing or treating cancer."

In order to test whether bacteria alone could provide better immunity against cancer, the bacteria were given to mice on a normal diet.

These mice were also more resistant to tumor growth, but not when they were exposed to a diet lacking vitamin D.

Although there is no conclusive evidence, previous studies have suggested a link between vitamin D deficiency and cancer risk in humans.

To investigate this, the researchers looked at a data set of 1.5 million people in Denmark, which highlighted a link between low vitamin D levels and a higher risk of cancer.

A separate analysis of a group of people with cancer also indicated that those with higher levels of vitamin D were more likely to respond well to immune-based cancer treatments.

Bacteroides fragilis has also been found in the human microbiome, but more research is needed to determine whether the sunshine vitamin helps provide some immune resistance to cancer through the same mechanism.

“The main question we are currently trying to answer is how exactly does vitamin D support a good microbiome,” said Evangelos Giambazoulias, a former postdoctoral researcher at the Crick Institute and head of the Cancer Immune Surveillance Group at Cancer Research UK’s Manchester Institute. "If this question is asked, we may discover new ways in which the microbiome influences the immune system, which may offer exciting possibilities in preventing or treating cancer."

Cancer Research UK's research information director, Dr Nesharanthi Dogan, added: "We know that vitamin D deficiency can cause health problems. However, there is insufficient evidence to link vitamin levels to cancer risk. This early research in mice, along with... Analysis of Danish population data addresses the evidence gap.

He continued: “While the results indicate a possible link between vitamin D and immune responses to cancer, more research is needed to confirm this.