Vitamin D has long been known to be a key player in the health of your bones, but in recent years research has also uncovered some of the other ways vitamin D affects your body. For example, vitamin D seems to play a significant role in the functioning of the immune system and there are some indications that it may have roles in the brain and heart. A new study published this week has added support to a growing base of data that vitamin D may also play as one of the body’s defenders against cancerous growth.
What is vitamin D?
Vitamin D is a vitamin made by your body with the help of sunlight. Its building blocks are made in your skin, where sunlight helps perform a needed step to turn those precursors together into a preliminary version of vitamin D. Unfortunately, that initial form isn’t ready to be used by the body. Instead, it circulates through the blood and is modified first by the liver and then by the kidneys. Once converted to its active form (called 1,25 dihydroxy vitamin D or calcitriol), it can circulate to the bones, kidneys, and various other organs where it’s needed for healthy function. Vitamin D is uncommon in food, but can be found in fatty fish, beef liver, cheese, and egg yolks. (Here’s a grocery list of foods that have vitamin D.) Some foods, like milk for example, also have vitamin D added to them.
What do we know about vitamin D’s link to cancer?
The link between vitamin D levels and cancer was first proposed by some researchers who noticed that colon cancer seemed to kill more people at higher latitudes than in areas close to the equator. That seemed to suggest that more sun exposure, which is needed for the body to make vitamin D, might be helping to lower colon cancer risk in some unknown way. Since then, several studies have looked at the possible link, but only rarely in a way that could do more than show a possible link.
The problem with that possible link is that it’s hard to tell if the two items are truly related. It might be, for example, that people who live closer to the equator eat fruits and vegetables found only in that region that help lower colon cancer risk and that vitamin D actually has nothing to do with it. To get around this, one study actually gave women vitamin D and followed them for several years to look at cancer rates, but that study hadn’t looked to see how much of that vitamin D actually got in the blood and what blood level might be needed to help keep cancer away. That’s where this research comes in.
How did these researchers investigate blood levels of vitamin D and cancer?
The researchers brought together two data sets to get a better handle on whether vitamin D was truly changing a person’s risk for getting cancer. The first data set came from the study mentioned above that had included samples mainly from a population of women in Nebraska. To that group they added data on cancer and vitamin D levels from a research team that had been collecting health information on individuals from across the U.S. Including both of these groups meant the researchers could look at a broader range of vitamin D levels in the blood for a larger group of people at a variety of different time points. This way they could look in more detail at how vitamin D levels might be related to cancer.
What did the researchers find?
The team found a clear relationship in all of their analyses between higher levels of vitamin D in the blood and lower levels of all types of cancers except skin cancers. Skin cancer is often an exception to the rule likely because sun exposure, which is needed for making vitamin D, can also increase skin cancer risk. This is not true for other types of cancer. In particular, the researchers found the biggest differences in cancer risk between women who had 40ng/mL or more of active vitamin D in their blood and women who had 10ng/mL or less in their blood. Those with higher levels had significantly lower cancer risk.
It’s important to note that the researchers didn’t have data on each person’s diet, physical activity, alcohol, or smoking use, all of which can influence a person’s risk for cancer. While these might not seem related to vitamin D, a person with a better diet or who exercises more might be more likely to get sun exposure and also less likely to have cancer. While these people might have a lower risk of cancer, it would be because of their diet or exercise even if their vitamin D levels are higher.
How does this apply to me?
This study helps confirm the importance of vitamin D in general human health and indicates that having more could help lower your cancer risk. Beyond that, it also drives home the point that blood levels matter when it comes to vitamin D. While it can be helpful to take a vitamin D supplement if you’re deficient in vitamin D, how much it helps depends on how much you take, how much is absorbed, and how much is circulating in your blood as a result. If you’re concerned that you might be low in vitamin D, it’s best to talk to your doctor before taking anything so that you can check to see if your vitamin D levels are actually low. Your doctor can also discuss with you how best to bring your level up into a healthy range if you are low in vitamin D.