Vitamin D supplements may prolong life for those living with cancer, new research suggests.
Researchers at Michigan State University (MSU) in East Lansing analyzed data from randomized controlled trials that had compared people who took vitamin D supplements with those who took a placebo for at least 3 years.
They only included trials that had examined the use of vitamin D supplements to prevent disease over a minimum follow-up of 4 years and had also recorded the incidence of cancer and cancer-related deaths.
In all, the analysis took in 10 trials with a total of 79,055 participants. Their average age was 68 years, and 78% of them were female.
The team found a significant link between the use of vitamin D supplements and a lower risk of death to cancer over the follow-up period.
The analysis showed that people who took vitamin D supplements had a 13% lower risk of dying from cancer than those who took a placebo over the same period.
There was no significant association, however, between vitamin D use and prevention of cancer.
The findings featured at the annual meeting of the American Society of Clinical Oncology (ASCO) in Chicago, IL, on June 3, 2019.
A recent supplement of the ASCO's Journal of Clinical Oncology also includes an abstract of the study.
"The difference in the mortality rate between the vitamin D and placebo groups was statistically significant enough that it showed just how important it might be among the cancer population," says Tarek Haykal, a resident doctor in internal medicine at MSU and one of the study's lead authors.
Cancer and vitamin D
According to the World Health Organization (WHO), cancer is the second main cause of deaths worldwide. In 2018, around 18.1 million people found out that they had cancer, and 9.6 million died of the disease.
Under normal circumstances, when cells undergo damage or grow old, they die, and new ones replace them. Cancer arises when this process stops working properly, meaning that damaged or old cells do not die, or too many new cells form. This dysfunction can result in a surplus of cells that grow out of control.
As a cancer tumor grows, it begins to spread into nearby tissue. At the same time, cells can escape the tumor, spread through the lymph system and bloodstream to other parts of the body, and start new, secondary tumors.
The chances of surviving cancer are much higher when diagnosis occurs in the early stages and treatment can begin before the disease has started to spread. Once cancer has spread, or metastasized, it is harder to treat.
Most people get their vitamin D from exposure to sunlight and from food. Some also take vitamin D supplements. The body has to convert vitamin D into an active form before it can use it. This process occurs in two stages: first in the liver, and then in the kidneys.
Once it is in an active form, vitamin D helps the gut absorb calcium during digestion and keeps blood levels stable for use in forming bone. It also helps maintain healthy bone. Health problems, such as rickets in children and osteoporosis in older people, can result from a lack of vitamin D.
As well as being essential for bone health, vitamin D also helps control cell growth, immune function, and inflammation. It performs these functions by regulating genes for cell differentiation, division, and death.
Outstanding questions need further research
An increasing number of studies have been looking at whether taking vitamin D supplements could prevent osteoporosis, cardiovascular disease, diabetes, cancer, and other diseases.
Haykal and his colleagues decided to take a look at this evidence in relation to cancer prevention, especially as the use of aspirin for "primary prevention of cancer is still controversial," they note.
While the study's findings are promising, Haykal says that there is still a lot to find out, including the correct dosage and blood levels of vitamin D.
There also needs to be more investigation into how many additional years of life vitamin D can give people with cancer and how the underlying mechanism of action works.
"There are still many questions, and more research is needed," Haykal urges. However, he suggests that the new findings are sufficiently strong to make him wish that more doctors would prescribe vitamin D, especially those caring for cancer patients.
"We know it carries benefits with minimal side effects," he argues, adding, "There's plenty of potential here."
"Vitamin D had a significant effect on lowering the risk of death among those with cancer, but unfortunately, it didn't show any proof that it could protect against getting cancer."