The unexpected role of this vitamin in the fight against cancer

The immune system is one of our primary defenses against cancer, yet sometimes it may need a boost. A recent study in mice suggests that vitamin D could provide this support. Let's explore what implications this might have for humans.

A class of drugs called "checkpoint inhibitors" releases the brakes on certain immune cells known as cytotoxic T lymphocytes, which then attempt to destroy cancer cells. These drugs can be highly effective in treating certain types of cancers, such as those of the skin, lung, and kidney, but unfortunately, they don't work for all patients.


Recent studies have shown that the microbiome of patients might play a role in this variation in response. In 2021, two studies demonstrated that by transferring microbes from the fecal matter of people responding to checkpoint inhibitor treatment to the guts of those not responding, therapeutic benefits could be enhanced in the latter group.

A surprising discovery in mice, revealed recently in the journal Science, suggests a potential explanatory factor for the varied responses individuals have to cancer treatments: the level of vitamin D in their gut might promote the growth of certain bacteria that encourage cytotoxic T lymphocytes to fight cancer.

Vitamin D, available from our diet or synthesized by our skin when exposed to sunlight, is essential for our metabolism and the health of our bones, muscles, nerves, and immune system. There are indications that it may also have a protective effect against cancer, but the recent observations in mice have been an unexpected revelation.

Caetano Reis e Sousa, an immunologist at the Francis Crick Institute in London and the lead author of the study, emphasizes that extensive research will be necessary to determine if the same processes are at work in humans, but this investigation is worthwhile. "Vitamin D influences the activity of many genes, which makes the situation complex," he explains. However, in several data sets analyzed, patients with increased vitamin D activity showed better survival against various cancers and responded more positively to immunotherapy.

Scientists have also found indications in Denmark, where sunlight exposure is less frequent and thus less conducive to human skin producing vitamin D. Detailed medical records revealed that individuals deficient in vitamin D had an increased risk of developing cancer over the next decade. "This is probably an underestimate," says Reis e Sousa, "as at least some of these individuals would likely have opted for vitamin D supplements upon learning of their deficiency."

This study provides another reason to ensure sufficient production or consumption of vitamin D, explains Carsten Carlberg, a biochemist at the Polish Academy of Sciences in Olsztyn, who has studied the effects of the vitamin for decades and did not participate in the Science study. However, he cautions against drawing hasty conclusions about ourselves based on results from mice. As he points out: "There are 75 million years of evolution that separate mice from humans."