Edam cheese has more vitamin K2 than other cheeses. (Photo by Sifu Renka)
Vitamin K2 hasn't really made it into the mainstream yet, but a lot health blogs have caught up on its importance.
One explanation is that vitamin K2 fits poorly into the conventional view of what is healthy, and everything that the conventional view disapproves of, contrarian health bloggers embrace. The irony of vitamin K is that contrary to what one might expect, vitamin K1 just doesn't seem to have the same punch as vitamin K2.
And the interesting difference between the two? The main dietary source of vitamin K1 (phylloquinone) in the Western world is green leafy vegetables, while the main sources of vitamin K2 (menaquinones) are meat and cheese.
For some people, advocating meat and cheese over green leafy vegetables is pure blasphemy, but when it comes to prostate cancer, it may not be such a bad idea. In this post, we'll take a look at a large study that found a reduced risk of prostate cancer in men who ate more vitamin K2 in their diet.
The EPIC study and dietary vitamin K intake
The European Prospective Investigation into Cancer and Nutrition (EPIC) is the largest study of diet and disease to be undertaken. It has more than half a million participants, most of whom are 35-70 years old. The study begun many years ago and is still ongoing, with results being published every now and then.
One of the papers from last years looked at the incidence of prostate cancer in the Heidelberg cohort of the EPIC study (link). The Heidelberg cohort included almost 12,000 men aged 40-65 years from Heidelberg, Germany. Their dietary intake of phylloquinone and menaquinones was assessed by using a food-frequency questionnaire and a list of the vitamin K content of ~2000 commonly consumed foods.
The median daily intakes of phylloquinone and menaquinones were 93.6 micrograms and 34.7 micrograms, respectively. Menaquinone-4 (MK-4) accounted for 14.4 mcg of total menaquinones, while menaquinone-7 (MK-7) accounted for only 0.8 mcg. The main dietary menaquinones in terms of quantity appear to be MK-4 and MK-9.
Vegetables, especially green leafy vegetables, were the main source of vitamin K1. In the case of vitamin K2, meat products were the main source of MK-4 and dairy products the main source of higher menaquinones. Since fermented dairy products contain only a very small amount of MK-7, and the only food that has a lot of it is natto, it's not surprising MK-7 intake was so low among participants. Nonetheless, even small amounts may be enough to see benefits.
Perhaps unsurprisingly, those who consumed more vitamin K appeared to be healthier in general:
Subjects in the upper quartiles of phylloquinone and menaquinones had a lower body mass index, were more likely to have a university degree, and were more likely to practice vigorous physical activity >2 h/wk than were subjects in the lower intake quartiles.
This was despite the fact that as the intake of vitamin K increased, so did energy intake. Smoking status, however, was not significantly different between quartiles of vitamin K intake. These factors, along with things like calcium intake and family history of prostate cancer were adjusted for in the multivariate analysis.
Dietary intake of vitamin K1 & K2 and prostate cancer
The analysis showed that dietary intake of phylloquinone was not associated with the incidence of prostate cancer. In other words, those who ate more vitamin K1 had just as much prostate cancer as the ones who ate less vitamin K1.
Menaquinone intake, on the other hand, was inversely related to the risk of prostate cancer after excluding cases who were diagnosed within the first two years of follow-up. When the authors looked at only advanced cases of prostate cancer, the inverse relationship was even clearer. Thus, in contrast to vitamin K1, those who ate more vitamin K2 had less incidences of advanced prostate cancer.
The food source of vitamin K2 was also important. Only menaquinones from dairy products were associated with a significantly lower risk of advanced prostate cancer, while those from meat products were not. Accordingly, the risk of advanced prostate cancer was lower in those who consumed more MK-5–9 but not in those who consumed more MK-4. In contrast, menaquinone intake from meat products were associated with a lower risk of all cases of prostate cancer, but this difference was not statistically significant.
If one were to interpret these numbers literally, then, it would seem that an increased intake of MK-4 (from meat sources) may reduce the risk of prostate cancer in general, while an increased intake of higher menaquinones (from dairy sources) reduces the risk of advanced prostate cancer.
So why would vitamin K2 reduce advanced prostate cancer but not total prostate cancer? The authors offers a possible explanation:
Our findings of stronger associations of vitamin K intake with advanced than with total prostate cancer could be a hint that menaquinones play a role in tumor promotion and progression rather than in tumor initiation.
In other words, vitamin K2 may not decrease your odds of getting prostate cancer, but if you do get it, menaquinones decrease the odds of the cancer reaching an advanced stage. This makes sense, given that menaquinones have been shown to have an antiproliferative effect on several cancer lines in vitro.
An increased intake of menaquinones (vitamin K2) but not phylloquinone (vitamin K1) is associated with a reduced risk of advanced prostate cancer. Based on this study, the main sources of vitamin K2 in the Western diet are meat and dairy products.
When comparing different food sources of vitamin K2, dairy products were more strongly associated with a reduced risk of advanced prostate cancer than meat products. Accordingly, higher menaquinones (MK-5–9), which are found mostly in dairy products, were more strongly inversely associated with prostate cancer than MK-4, which is found mainly in meat.
For more information on diet and cancer, see these posts:
Red Meat and Mortality: A Closer Look at the Evidence
Green Tea Catechin Reverses the Effect of DHT in Prostate Cancer Cells
Intermittent Fasting Reduces Mitochondrial Damage and Lymphoma Incidence in Aged Mice
Slowing Down Aging with Intermittent Protein Restriction