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.
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.