Vitamin D No Magic Bullet for Cancer

We have been bombarded over the last couple of years with scientific articles suggesting that vitamin D is the key to improving many aspects of our health, including reducing the risks of dying from cancer.

An article in this week's Journal of the National Cancer Institute reminds us that perhaps we should be a bit cautious in embracing vitamin D as "the answer" before we do more research.

The report, from the National Cancer Institute and the Centers for Disease Control and Prevention, concluded that vitamin D levels in the blood were not related to overall cancer mortality.

However, the study did find that higher levels of vitamin D were associated with a substantial decrease in the risk of dying from colorectal cancer, and possibly with a reduction in the risk of dying from breast cancer.


The study was performed between 1988 and 1994 and was designed to examine the health and nutritional status of the noninstutionalized U.S. population.

A total of 16,818 people were part of the study, which continued with follow-up through the end of 2000.

The researchers monitored a number of factors, including race/ethnicity, the latitude where the people lived (which would be expected to influence vitamin D levels through sun exposure), smoking, educational levels and physical activity, among other variables.

The key finding of the study was that there was no impact of vitamin D levels on the overall risk of dying from cancer, when comparing groups based on where they lived or what season their blood test was drawn.

When the researchers broke down the risks of cancer deaths based on a number of cancer sites, the only significant reduction they found was for colorectal cancer. In this cancer, those people with higher levels of vitamin D had a risk of dying from this disease that was 72 percent less than people with lower levels of vitamin D.

Although the data for breast cancer was suggestive of a protective effect of vitamin D, the numbers were insufficient to rule out other possible explanations for the decreased risk of death from breast cancer noted in the study.

No Death Knell for Vitamin D Benefits

Why would this study find results that appear to contradict the several other studies that have recently reported decreased risks of cancer deaths for a variety of cancers?

First, it's important to note that no study is perfect — not even this one. Many other studies that have been reported to show a decrease in cancer deaths related to higher vitamin D intake or sun exposure have been done by excellent researchers from highly regarded institutions.

This study stands out because it was done prospectively. That means the participants were followed looking forward, and there were actual blood tests that measured vitamin D in the blood.

Many of the other studies have tried to infer vitamin D levels through a variety of means, such as asking about dietary habits or inferring a vitamin D level based on descriptions of outdoor activities.

That doesn't mean that one study is right and the other is wrong. It simply means that different researchers have reached different conclusions based on the analysis of different types of information.

For example, in this JNCI study, the numbers of certain cancer deaths may have been too small to reach an accurate conclusion. Or, perhaps the follow-up wasn't long enough, or perhaps the impact of vitamin D would have been greater if the blood test had been performed in younger people who were then followed for many more years.

The authors concluded with a statement that "additional studies with large numbers of samples of measured (vitamin D) levels, preferably at multiple time points, are needed to confirm the total cancer mortality findings of this paper and to obtain more accurate risk estimates for mortality from specific cancers."

An editorial in the same issue of the Journal agrees, and I particularly appreciated the conclusion of this editorial:

"Whether vitamin D reduces cancer risks and, if it does, whether these amounts suffice are actively being debated. Randomized clinical trials of the effects of vitamin D on the incidence of colonic polyps and invasive cancer are needed. While vitamin D may well have multiple benefits beyond bone, health professionals and the public should not in a rush to judgment assume that vitamin D is a magic bullet and consume high amounts of vitamin D. More definitive data on both benefits and potential adverse effects of high doses are urgently needed."

I couldn't agree more.

More Research Needed

Since vitamin D has come into the spotlight, I have transitioned from being a skeptic to believing there may in fact be a role of vitamin D in reducing the risks of a variety of cancers. The evidence has been inferential, but I can't ignore the weight of that evidence suggesting that such a relationship exists.

But the American Cancer Society has resisted the temptation to draw the conclusion that we currently know enough to make a general recommendation to the more than 300 million people in this country (and throughout the world) that they should markedly and routinely increase their vitamin D intake.

We have consistently called for more research into this topic. This is especially important given our past experience with other vitamins, such as vitamin C and beta-carotene, where well-qualified experts touted the benefit of those vitamins in reducing cancer risk.

When the studies were actually done, we discovered that the vitamins had either no effect or, for some people, may have actually increased their risk of cancer.

So what is the bottom line? Is this study the end of the vitamin D debate (except perhaps for colorectal cancer and breast cancer)?

I don't think this study should end the discussion of the possible role of vitamin D in cancer prevention, any more than I think the other studies answer the question that we need to embark on a major nationwide effort to increase vitamin D intake to supernormal levels.

We need more research, we need more information and we need to answer the question definitively.

Until we get those research studies, it is essentially an individual decision what to do, perhaps in consultation with your medical professional.

We do not have all the answers about the possible benefits of vitamin D in preventing cancer (or lack thereof), and we don't have all the information about the risks.

Hopefully, as this debate continues, we will be able to move the research agenda forward and provide solid answers and guidance to replace the uncertainty that many of us currently face regarding the role of vitamin D in cancer prevention.

Len Lichtenfeld is deputy chief medical officer of the American Cancer Society. You can view the full blog by clicking here.