Vitamin D apparently has a preventive effect against cancer by stimulating the growth of certain intestinal bacteria. A good supply of vitamin D could be crucial for both cancer prevention and the success of immunotherapy.
A research team from the National Cancer Institute (NCI) in the US and Aalborg University in Denmark has found that vitamin D promotes the growth of a type of gut bacteria in mice that improves immunity against cancer. The corresponding study results are published in the specialist magazine “Science”.
Cancer and vitamin d
Numerous previous studies have already suggested a connection between vitamin D and cancer and, for example, linked a vitamin D deficiency to an increased risk of cancer or found a significantly reduced cancer mortality with daily vitamin D intake.
On the other hand, it has already been proven that the intestinal microbiome influences the success of cancer treatments and that the intestinal flora has an impact on the risk of cancer, with the effect apparently being mediated by certain immune cells.
In the new research, the team has now investigated whether vitamin D may influence microbiome-dependent cancer immunity and thus have an anti-cancer effect.
Examining the connection
First, the researchers analyzed a data set from 1.5 million people in Denmark and were able to show a connection between lower vitamin D levels and a higher risk of cancer.
Separate analysis of a cancer patient population also suggested that people with higher vitamin D levels were more likely to respond well to immune-based cancer treatments, the experts report.
Better immune resistance thanks to intestinal bacteria
In studies on mice, the team was also able to show that when they were given a diet rich in vitamin D, they had better immune resistance to experimentally transplanted cancers and responded better to immunotherapy.
Surprisingly, the influence of vitamin D on epithelial cells in the animals' intestines led to an increase in the amount of a bacterium called Bacteroides fragilis, the researchers explain. This bacterium improved immunity against transplanted tumors so that they grew less vigorously.
To test whether the bacteria alone could provide better cancer immunity, the team then administered Bacteroides fragilis to mice on a normal diet. The animals were also better able to resist tumor growth, but not when they were placed on a vitamin D-deficient diet.
Although the researchers are not yet sure why the bacteria inhibit cancer growth, the overall results suggest that vitamin D also has an anti-cancer effect through its influence on the intestinal flora.
Impact on cancer therapy?
“This could one day be important for cancer treatment in humans, but we do not know how and why vitamin D has this effect across the microbiome,” said study author Caetano Reis e Sousa.
“A key question we are currently trying to answer is how exactly vitamin D supports a 'good' microbiome. If we can answer this question, we could uncover new ways in which the microbiome influences the immune system, potentially offering exciting opportunities in preventing or treating cancer,” adds study author Evangelos Giampazolias.
Further studies are now needed to fully understand the underlying mechanisms for the effect of vitamin D against cancer and to find out how this can be used to develop personalized treatment strategies, the researchers conclude. (fp)
