Vitamin D Supplements Do Not Lower Risk of Cancer

By National Cancer Institute Staff

In the largest-ever randomized clinical trial testing vitamin D for cancer prevention, the supplement did not reduce the risk of developing cancer.

A large body of epidemiology research had suggested that people with higher blood levels of vitamin D have a lower risk of cancer, said Barry Kramer, M.D., director of NCI’s Division of Cancer Prevention.

However, such studies can only highlight associations, not prove cause and effect, he added. “This is why it’s important to question intuitions and observational epidemiology studies, and fund large-scale trials,” Dr. Kramer continued; they can conclusively show whether a treatment—in this case, a dietary supplement—truly can help to prevent cancer.

Results from the trial, called the Vitamin D and Omega-3 Trial (VITAL), were published November 10 in the New England Journal of Medicine (NEJM).

Isolating the Effects of Vitamin D

The body produces vitamin D when the skin is exposed to sunlight. The vitamin is also found naturally in some foods, such as fatty fish and mushrooms, and is often added to others, including milk and some cereals.

For people with known vitamin D deficiencies, supplementation is recommended to maintain bone health and prevent fractures. “The main goal of VITAL was to see if there’s benefit to getting above the recommended dietary allowance, more than what is considered necessary for bone health,” explained JoAnn Manson, M.D., of Brigham and Women’s Hospital and Harvard Medical School, who led the study.

Observational studies have suggested that people who take vitamin D supplements may have a lower risk of many diseases. But “people who take vitamins may be very different in important ways from people who don’t take vitamins,” explained Dr. Kramer. They often have a higher income and are less likely to smoke, less likely to be overweight, and more likely to have health insurance, he added—all of which are strongly linked with a lower risk of a variety of chronic health conditions, including heart disease and many cancers.

Large randomized clinical trials with thousands of participants can avoid these biases by randomly assigning study participants to receive or not receive the treatment.

VITAL was designed so that it could study the effects of both vitamin D and omega-3 supplements. The trial’s primary endpoints—the key outcomes it measured—were the supplements’ impact on the risk of developing cancer and heart disease. It also had several secondary endpoints, including the risk of dying from cancer. VITAL was funded primarily by NCI and the National Heart, Lung, and Blood Institute.

Almost 26,000 participants with no history of invasive cancer or cardiovascular disease enrolled in the trial. Men had to be age 50 or older, and women age 55 or older, to enroll in the study. About half of the participants were women, and the participants were racially diverse, with about 20% being African American.

“The number of participants and the substantial proportion of black participants make this cohort a nationally representative sample,” wrote John Keaney, M.D., and Clifford Rosen, M.D., of the University of Massachusetts Medical School and the Maine Medical Center Research Institute, in an accompanying editorial.

Participants were randomly assigned to one of four groups: daily vitamin D plus a placebo, omega-3 supplements plus a placebo, both vitamin D and omega-3 supplements, or two placebos. The researchers followed the participants for a median of 5.3 years.

About 17,000 participants provided blood samples at the start of the trial, 1,600 provided a second sample a year into the study, another 5,000 provided follow-up blood samples at later time points. The researchers used these samples to measure blood levels of vitamin D and omega-3s in the different groups.

Higher Vitamin D Levels Did Not Lead to Greater Benefit

Participants taking vitamin D saw their blood levels of the vitamin rise by 40% on average during the trial. However, despite this rise, the incidence of invasive cancer was about the same between the groups: 793 participants in the vitamin D group (6.1%) received a cancer diagnosis during the trial, compared with 824 in the placebo group (6.3%). The incidence of cardiovascular events (such as heart attacks) was also similar between the vitamin D and placebo groups.

Over the follow-up period, there were 341 deaths from cancer: 154 among participants who took vitamin D (1.1%) and 187 among those who took the placebo (1.4%). Although this difference was not statistically significant, the difference in cancer deaths between the groups started to widen over time, the researchers reported.

The researchers plan to follow the participants for another 2 to 5 years, to see if a statistically significant difference in cancer deaths emerges. Laboratory studies have suggested that high blood levels of vitamin D may decrease the aggressiveness of cancer cells and the likelihood of metastasis, explained Dr. Manson. If so, longer follow-up will be needed to assess its effects on the risk of death from cancer, she added. Other studies have suggested that regular use of vitamin D supplements may reduce the risk of dying from cancer, she said.

Supplementation with omega-3 fatty acids also did not significantly reduce the risk of cancer incidence or cancer death. Those results were presented in a separate paper, also published in NEJM.

No increased risk of side effects—including high blood calcium levels for vitamin D, bleeding with omega-3s, or gastrointestinal upset for either supplement—were found among people taking the supplements at these doses, compared to rates in the placebo groups.

Future Paths for Vitamin D Research

The VITAL trial “was well designed,” said Dr. Kramer. “And when it’s important to get the answer right— that is, when you’re potentially making recommendations to hundreds of thousands, or even millions, you want to make sure that your recommendations are based on very strong evidence,” he added.

Other research into vitamin D and cancer prevention is ongoing, such as studying whether some types of cancer may be more sensitive than others to the effects of supplementation.

For example, an NCI-sponsored clinical trial is currently looking at whether supplementation with vitamin D, calcium, or both can prevent the development of new colorectal adenomas in people who have already had one or more such precancerous growths removed. VITAL will also examine effects of the supplements on the risk of new colorectal adenomas.

Dr. Manson and her colleagues plan to follow the participants for at least 2 more years and hope to secure grant funding to follow them for a longer period, she said. They would also like to study the potential influence of genetics on the effects of vitamin D supplementation.

“This is something we really want to look at—whether there are gene variants related to vitamin D metabolism, the vitamin D receptor, binding proteins, or even completely separate mechanisms, that could have influenced the effects of supplementation and could help identify those most likely to benefit,” Dr. Manson said.

The VITAL results don’t give reason for people taking vitamin D as recommended by their doctors to stop, she continued.

“If you have a clinical indication for taking vitamin D, such as a bone health problem or malabsorption condition, or use of other medications that interfere with the bioavailability of vitamin D—then of course you should keep taking it,” she concluded.


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  1. notice it was done by the National Cancer Institute …hardly a neutral organization.

    vit D has a roll in virtually every cell in your body…..
    Ideally your blood level of vit-D should be 50–80 ng/ml…..and even higher 70/100ng/ml..if treating cancer/heart disease….levels impossible to achieve by giving everyone the same dose of 2000IU /day…as in the study.

    that one issue alone….makes this study…INVALID.

  2. In the article where it claims, “…341 people died of cancer…”, one must verify how this claim was proved. For example when a cancer patient is under orthodox treatment, and dies, they could have died from the cancer or treatment or both, usually treatment because all treatments are life threatening, but falsely reported has having died from cancer. The only way to prove the cause of death is from a thorough autopsy by a top independent laboratory which is rarely done. Just because a patient has cancer and dies does not mean they died of cancer. My wife was nearly killed from treatment but if she had died they would have falsely claimed she died of inflammatory breast cancer when the “treatment” made a hole in her colon and allowed clostridium septicum bacteria into her bloodstream from which most patients die in 24 hours. She would have died from the treatment, not the cancer but they would have likely lied about it because they don’t want to admit the treatments kill more patients than the cancer does. Her local doctor sought to lie about this but her doctors at MD Anderson in Houston admitted verbally this was correct. Luckily she did not die but came very very close to dying due to this scenario happening to her. She was on a ventilator in a vegetative state for 11 days. The local hospital charged $72,000 to keep her alive when they nearly killed her! She then moved to Houston, Texas where the remainder of her treatment was performed with no further terrifying events. She had to live there over a year. Her treatment there cost over $300,000! But they did fully cure her and she is still alive today some 20 years later. If you have cancer your best shot is with a top institution like MD Anderson in Houston, Texas. These local hospitals are much more likely to kill you or your loved ones. They are not set up for the complex process of treating cancer patients.

    • I would urge everyone interested in cancer to read the book “The Hidden Story of Cancer” by Brian Peskin, E.E. and Amid Habib, M.D., Pinnacle Press, Houston, 2006-2010. This great book has a detailed and readable discussion of the seminal experiments and facts developed by the genius level scientist Otto H. Warburg, M.D., Ph.D. (1883-1970) on cancer in Germany. Warburg was considered the greatest biochemist of the 20th century. He developed experiments and facts which proved that cancer is caused by oxygen deficiency to living cells over a relative long period of time for humans. He first studied rats in the 1920’s but it took about 40 more years to prove the results for humans by about the 1955-1965 period. Your body has roughly 100 trillion cells. Every one must be saturated with oxygen at all times. If not, the cell dies or switches to running on sugar anerobically leading to cancer, called fermentation. He proved this with experimental facts, not genetic speculations. But the orthodoxy hated his guts because he remained in Germany his entire life. They have been in denial about his results based on experiments and facts. Brian, a top electrical engineer from MIT got interested in health issues. He makes intelligent recommendations of using Omega 3 and Omega 6 EFA’s, which he describes as “Oxygen Magnets” to get oxygen to all those 100 trillion cells in your body a big job. This is a very readable book which required reading papers by Warburg published everywhere, mostly in German. Warburg was the best of the best. He was awarded a solo Nobel Prize in 1931 for his work on Cell Respiration. He was nominated for the first cancer prize in 1926 but given to Fibiger whose work was shown to be wrong. He was nominated again for a third Nobel Prize for yet different work in 1944 but denied by Hitler’s decree. Warburg’s Father was a top physics professor at Berlin and held the Chair of Physics there until his death in 1931. He and his Father were the best of the best. The orthodoxy of the U.S. has it wrong about cancer. They have cause and effect mixed up.

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