Vitamins C and E don’t protect against prostate cancer; what about vitamin K?
Posted Apr 01 2010 12:00am
Data from a prospective study now suggest an association between dietary levels of vitamin K and one’s risk of developing or dying from colon, breast, prostate, or lung cancers.
We should be clear, up front, that this German study by Nimptsch et al. does not prove that higher levels of dietary vitamin K help to lower the risk for these cancers, nor do the researchers suggest that they might prove this. Rather, these data provide a hypothetical basis for future studies of that question.
There are two basic types of vitamin K: phylloquinone (vitamin K1) and the menaquinones (vitamin K2). Because vitamin K has been shown (in animal and cell line studies) to have anticarcinogenic activity, the authors decided to test whether the amounts of these vitamins in people’s diets might be associated with the incidence and mortality rates of specific common forms of cancer in a large cohort of people.
The authors were able to carry out this study among 24,340 people comprising the Heidelberg participants in the prospective European Prospective Investigation into Cancer and Nutrition (EPIC) study. All participants in this study were aged between 35 and 64 years and were free of cancer at enrollment (from 1994 to 1998). They were then actively followed up for cancer incidence and mortality through 2008. The dietary vitamin K intake of all study participants was estimated based on data in food-frequency questionnaires completed at baseline. (This is probably not the most accurate method for assessing dietary intake of vitamin K.)
The results of the study show the following:
At a follow-up of >10 years, 1,755 incident cases of cancer were identified, of which 458 were fatal.
Dietary intake of menaquinones was inversely associated with overall cancer incidence but this association was not statistically significant.
Dietary intake of menaquinones was more significantly associated with cancer mortality.
A higher intake of dietary menaquinones was associated with a higher probability of cancer risk reduction in men than in women, largely as a consequence of the inverse incidence associations for prostate cancer and lung cancer.
There was no association between phylloquinone dietary intake and risk for cancer diagnosis or mortality.
All results are given after taking account of other factors, such as age, weight, exercise habits, smoking, and consumption of other specific nutrients, like fiber and calcium.
The menaquinones (vitamin K2) are usually found in things like meat and cheese, and in this study it is reported that participants most frequently obtained their vitamin K2 from the amount of cheese in their diet.
To put some specific numbers to the results, the research team showed that the 25 percent of participants (quartile) with the highest intakes of vitamin K2 in their diet were 28 percent less likely to have died of any one of the four cancers studied than the quartile with the lowest intakes of vitamin K2. In addition, in the quartile with the lowest dietary intake of vitamin K2, 156 participants (2.6 percent) died of one of the four cancers. Conversely, for the quartile with the highest dietary intake of vitamin K2, only 1.6 percent died of cancer.
With respect to prostate cancer specifically, there were 111 cases among the quartile of men with the lowest vitamin K2 intakes, but only 65 cases in the quartile with the highest consumption of vitamin K2.
In theory, this study suggests that vitamin K could offer some protection against cancer on its own, but the research team states that, in their opinion, it is unclear whether vitamin K intake itself is responsible for the lower cancer risks. The researchers are planning a second step to their research in which they want to measure vitamin K levels in people’s blood and then examine whether there is any relationship between those levels and levels of cancer risk.
It is worth noting that, in this study, men in the quartile with the highest level of dietary vitamin K intake were taking ≥ 92 μg/day or more, and their female counterparts were taking ≥ 84 μg/day. By contrast, the recommended daily intake for vitamin K, in all forms, in the USA is 120 μg for men and 90 μg for women.
The “New” Prostate Cancer InfoLink would be extremely surprised if any large, randomized, clinical trial were ever to prove that one particular vitamin, taken at a specific dosage level over a well defined period of time, had a large and statistically significant impact on the prevention of any cancer (including prostate cancer). However, we believe it is very possible that a well-balanced dietary intake of vitamins is associated with a statistically significant impact on one’s overall risk for cancer and cancer-specific mortality over a lifetime by comparison with an unbalanced dietary intake of the same vitamins.