Does Vitamin D Offer Cancer Protection - Two Headlines Contradict Each Other

Here are two recent headlines from the news: "Vitamin D does not prevent death from cancer" and "More vitamin D could mean fewer cancers: study". Both came out within 60 days of each other. How is the average person supposed to know whether vitamin D has any cancer prevention benefit or not? Here's what I decided after reading the details of each study.

First, lets look at the specific titles, they are not mutually exclusive. It could be that if you have higher levels of vitamin D you are less likely to get cancer, but more of those who do get cancer will die from it. Possible, but highly unlikely, let's discard this possibility for now. furthermore, it may be that Study B is correct that colon and breast cancer are reduced, but Study A would also be correct if, for example, this were compensated by higher incidence of some other type of cancer. However, there is no data to suggest a higher incidence of any form of cancer from higher levels of vitamin D (within normal limits), so it would be impossible to make this conclusion.

Second, let's look at the methodology of the studies.
Study A: vitamin D levels were checked at the start of the study and then cancer death rates were followed for 6-12 years afterward. So the real conclusion is that having a higher level of vitamin D at one given moment in time does not provide lasting cancer preventative benefit. In other words, if you take vitamin D pills for two weeks, it doesn't offer 6-12 years of benefit. This is a poorly crafted study which should have regularly measured vitamin D levels during the entire study period, in my opinion. Even so, they did find that death from colon cancer was reduced.

Study B: (I'll quote from Reuters here) "researchers at the University of California used data on average wintertime blood levels of vitamin D and rates of breast and colon cancers in 15 countries. They found that rates of the diseases tended to fall as average vitamin D levels climbed." This suggests that during periods when vitamin D levels are higher, cancer rates are lower. In other words, as long as one maintains a high level of vitamin D, there is likely to be some cancer preventative benefit (for breast and colon cancer). Study B's methodology seems much stronger. However, the evidence is for an assocaition of vitamin D levels and lower rates of breast and colon cancer, and can't scientifically say one causes the other. More research would be needed for that.

Both studies, need follow up studies to firmly make the case either way, with more well thought out methodology. However, they BOTH seem to find evidence that incidence of colon cancer is substantially reduced by higher vitamin D levels. Furthermore, laboratory studies show that cancer cell growth and spread is inhibited by exposure to vitamin D.

I did NOT have access to the full studies and based this upon what was reported in various news outlets. News outlets are not always reliable in their interpretation and reporting of study results and methodologies, so there is some chance that I am not in possession of key data from these studies that would change my opinion, but for now this is the best I have to go on.

My vitamin D conclusion: Very moderate exposure to sunlight and/or regular vitamin D supplements is safe and the preponderence of evidence suggests it will reduce the incidence of colon cancer (and perhaps breast cancer). Note that reduced incidence doesn't mean you can't get it, just that the odds are less that you will. There are also other health benefits for vitamin D supplementation supported by other research. Because there is extremely low risk for taking vitamin D supplements, I feel that this is enough information for me to take vitamin D with the goal of reduction in likelihood of breast and colon cancer. So how much to take? The US Recommended Daily Allowance is 200 IU for young adults and 600 IU for older adults. other studies suggests that is on the low side. My lay opinion: for any adult age, taking a 600 IU supplement in combination with dietary sources of vitamin D and very moderate sunlight exposure (which helps the body make more vitamin D available) should get you enough to provide measurable cancer protection and other substantial health benefits without any significant risk. This is not advice about what you should do, I am not a doctor. make your own decision in consultation with your doctor.

Sources:
Vitamin D does not prevent death from cancer , Reuters
More vitamin D could mean fewer cancers: study, Reuters