Breast Cancer

Do Vitamins Help Prevent Cancer? Strong New Evidence Argues “No”

Published Nov 10, 2018

For the millions of Americans taking vitamins in hopes it will reduce the risk of cancer and other diseases, major new medical research finds that two widely used vitamins fail to prevent cancer. Vitamin D and omega-3 fish oil had no health impact. Two studies of over 25,000 people,  compared Vitamin D and omega-3 supplements to placebo. After over five years of follow-up, there was no difference in the incidence of cancer or heart disease in those who took the vitamins compared to the people who took the placebo.

In recent years the use of vitamin D supplements, which have been used to prevent bone disorders, has grown significantly. Some studies have suggested that vitamin D might prevent cancer. But these are not the kind of studies of the highest quality, where people are given vitamins or placebo and followed over many years. There have also been questions about studies where people have been given lower doses of vitamin D. Was it possible if the dose were higher cancer would be prevented? There was also the fact that people with high levels of vitamin D tended to live longer. But that doesn’t mean the vitamin D was the reason.

The government appointed panel charged with making recommendations on ways to prevent disease concluded that there was not enough evidence on the effectiveness of vitamin D supplementation in preventing cancer or cardiovascular disease. There were also questions about whether omega-3 supplements could prevent cancer or heart disease. And so the study known as VITAL was launched to try and get an answer.

Beginning in 2011, 25,871 people were randomly assigned to receive Vitamin D, Omega-3 , or placebo. The men were 50 years of age or older. The women were 55 years or older. They were then followed for 5.3 years, and the number of new cancers for each group was added up at the end of the study. The results:

  • 793 cancers in the Vitamin D group
  • 824 in the placebo group

“No significant difference between the two groups were observed with regard to the incidence of breast, prostate or colorectal cancer,” the study said. And the incidence of death from cancer was no different. At a news conference Saturday, at the American Heart Association Scientific sessions where the study was presented, Dr. Jane Armitage of the University of Oxford said of the study results: “The cancer is robustly negative with over 1600 invasive cancers and no suggestion of any benefit.”

The study was led by Dr. JoAnn Manson, from Brigham and Women’s Hospital and Harvard Medical School, Manson and the other Harvard investigators are among some of the leading figures in these kinds of studies of large populations which look at disease risks and benefits. The study was published in the New England Journal. VITAL was sponsored by the National Institute of Health.

What’s most important in a medical study is the results for all of the people who participated in the trial. But researchers will often examine so-called subgroups in the study. When the VITAL study went looking at its subgroups it found “normal-weight participants experienced significant 24% and 42% …reductions in cancer incidence and mortality, respectively, whereas overweight and obese participants did not benefit.” And the African Americans  who took vitamin D had what was called “a suggestive 23% reduction in cancer incidence.”

The strength of the VITAL trial was described as “a large population sample with racial ethnic group and geographic diversity.” Five thousand one hundred of the participants were black. The study also used a high dose of vitamin D.  But there were also weaknesses. “Before we completely abandon suggesting that people take vitamin D supplementations it is important to note some unanswered questions,” said Dr. John Robbins, at the UC Davis Comprehensive Cancer Center.

Robbins noted that most of the people in the study had normal vitamin D levels. He wondered whether it’s possible that people with low levels of my vitamin D might benefit. “The 5 year follow-up time is also problematic,” Robbins said. It may take longer for cancer to develop than the five years of the study. “It is likely that if vitamin D is going to have an effect it needs to be taken before or early in the development of cancer,” Robbins said. So we don’t know whether the Vitamin D was taken at the right time for preventing cancer. The authors acknowledge the need for longer follow-up, and point out another limitation. Only one dose of vitamin D was tested. Perhaps a different dose might have produced different results.

Despite some of these weaknesses, this study has provided a powerful case for the lack of benefit in preventing cancer by taking vitamin D or Omega-3 supplements.


Learn more about SurvivorNet's rigorous medical review process.