Vitamin D & Cancer Prevention
Vitamin D is actually a number of fat-soluble secosteroids including Cholecalciferol (vitamin D3) and Ergocalciferol (vitamin D2). It is an interesting vitamin because the human body can either digest it via food or it can be obtained via exposure to the sun as the body synthesizes it. In that sense it’s not a dietary vitamin in the strict sense as it can come from the human bodies exposure to sunlight.
Vitamin D is essential for the development, growth and repair of human bones, aids in the absorption of calcium and helps the immune system function. Vitamin D also plays a role in improving muscle strength and reducing inflammation.
Vitamin D deficiency has been linked to a number of diseases including rickets (childhood osteomalacia), so in the developed world it is added to a number of food items like cow’s milk to avoid those illnesses. A lack of vitamin D can also play a role in the development of Osteoporosis. People with unusual diets and those who do not obtain enough sunlight are at risk of vitamin D deficiency. Between the ages 1-50, 5 μg (=200 IU) of vitamin D is recommended. After 50 most specialists recommend between 10 μg (=400 IU) and 15 μg (=600 IU) of vitamin D.
Vitamin D Studies
Recent studies have suggested that high levels of vitamin D may actually reduce the risk of colorectal cancer and studies are looking at further possible cancer risk reduction for prostate cancer, breast cancer and pancreatic cancers. This post will take a closer look at the accumulated evidence for vitamin D playing a role in cancer prevention.
Many scientific studies have been performed which look at vitamin D specifically. In early tests, scientists looked at the geographic correlation studies to see if people in more sunny areas of the planet (higher vitamin D intake) had lower risk of cancers. People living in the southern latitudes were found to have a lower incidence of certain cancers than people in the less sunny northern latitudes. From these early studies, scientists suggested that vitamin D played some role in cancer prevention.
In laboratory studies, vitamin D was used on cancer cells and found to have an impact on the growth of the cancer cells and in some cases even killed them. Laboratory studies using cultures are quite often vastly different from the how vitamins operate within the human body however.
Clinical human trials have determined that vitamin D high intake may reduce the risk of cancer. One trial involving 1250 older women who took a combination of calcium tablets and vitamin D tablets for 4 years saw a 60% lower incidence of cancer compared to the placebo taking group. However in that study, a vitamin D only group (without calcium) was not used. The study itself was designed to look at bone health so the cancer findings were supplementary.
Observational studies have been undertaken to look at vitamin D and it’s cancer prevention abilities specifically. The studies haven’t been conclusive so far, largely due to the difficulty of determining how much the patients diet impacts their chances of getting cancer. Quite often the data which is given by patients to researchers is also inaccurate, with their determination of their dietary intake being way off. At this stage many of the studies suggest their is possibly a link between higher vitamin D consumption and reduced cancer risk.
There is also a very close relationship between vitamin D and calcium in the body, so it is somewhat difficult to study just the effects of vitamin D when varying levels of calcium intake are involved in the mix. New randomized trials which look at vitamin D specifically are required.
Vitamin D and Colorectal Cancer
The data in this area is somewhat inconsistent, but findings indicate that there is some role for vitamin D in the prevention of colorectal cancer.
The American Cancer Society Cancer Prevention study which featured 120’000 men and women found that men who took 13 μg (525 IU) or more vitamin D per day in their diet had a lower risk of colorectal cancer. However, interestingly this reduced risk was not shown in women.
In a meta-study looking at 10 cohort studies, it was found that people who had very high vitamin D intakes had a slightly lower risk of colorectal cancer than those on the lowest intakes of vitamin D. However the risk was reduced by such a small amount it could have been a statistical anomaly.
In the Third National Health and Nutrition Examination Survey, a look at over 16’000 participants concluded that those with higher vitamin D blood levels (≥80 nmol/L) had a 72 percent lower risk of colorectal cancer death compared to those with a very low level of vitamin D in their blood.
Of the types of cancer, colorectal cancer prevention is the one most likely linked with high vitamin D intake.
Vitamin D and Breast Cancer
There have been conflicting results in epidemiological studies looking at the link between breast cancer risk reduction and vitamin D. Some studies find a link in risk reduction, but others find no such link. A meta-study involving six other studies saw no association between vitamin D intake and breast cancer risk reduction. That being said, the studies involved did not have very high vitamin D intakes required, and when the study only looked at the very high intakes (>10μg) compared to the very low (<1.25μg) there was a reduced risk in breast cancer found.In another large study which involved many thousands of women taking calcium and vitamin D supplements, there was no reduced risk of invasive breast cancer found.
Vitamin D and Prostate Cancer Risk
Geographic correlation studies (comparing people in sunny locations to less sunny), have found a link between vitamin D and reduced prostate cancer risk. However epidemiological studies have found no such link.
In a large study that looked at the incidence of prostate cancer in men a number of years after their blood was tested for vitamin D levels, high vitamin D blood levels did not have a link to reduced prostate cancer risk. If anything, there was a link between increased vitamin D intake and an increased risk of the aggressive prostate cancer.
Vitamin D and Pancreas Cancer Risk
There is some debate about the role of vitamin D in reducing pancreas cancer risk with some vastly different results. One study involving 120’000 men and women found that participants with higher intakes of vitamin D had a progressively lower risk of pancreas cancer compared to the lower intake participants. However, this study used questionnaires which involved patients estimating their diet and there vitamin D levels.
In a PLCO study, no link was found between vitamin D level and reduced pancreatic cancer risk.
Should you take vitamin D?
Vitamin D is essential for the functioning of the human body. If you do not get much sunlight exposure, and/or you are over the age of 50, vitamin D supplements might be a good idea just for maintaining good health. To identify any vitamin D deficiency, have a blood test done by your doctor.
As to whether vitamin D reduces the risk of cancer, there is a great deal of data for and against it. The strongest evidence is for colorectal cancer prevention. However if you are concerned about prostate cancer, taking high levels of vitamin D might in fact increase your risk. There is potential benefit, but also potential risk of prostate cancer for men. At this stage the best decision you could make, would be to consult with your doctor and determine your levels then decide if you need more vitamin D.