An increased intake of vitamin K2 may reduce the risk of prostate cancer by 35 per cent, suggest results from the European Prospective Investigation into Cancer and Nutrition (EPIC).
The potential benefits of K2 were more pronounced for advanced prostate cancer, while vitamin K1 intake did not offer any prostate benefits, report the researchers from the German Cancer Research Centre in Heidelberg.
The findings, based on data from the 11,319 men taking part in the EPIC Heidelberg cohort, are published in this month's issue of the American Journal of Clinical Nutrition.
The study, by Katharina Nimptsch, Sabine Rohrmann and Jakob Linseisen, adds to a small but ever-growing body of science supporting the potential health benefits of vitamin K, most notable for bone and blood health, but also recently linked to improved skin health.
The study has been welcomed by leading vitamin K researcher Cees Vermeer, PhD, from the VitaK and Cardiovascular Research Institute CARIM at the University of Maastricht, who told NutraIngredients.com that the study was "high quality."
"The anti-tumor effect of K2 vitamins has been suggested in several other (mainly Japanese) papers; in most cases these papers were based on smaller numbers, however. Also, in Japan it is usual to provide very high doses of the short-chain menaquinone-4 (45 mg/day or higher)," said Dr. Vermeer.
"The elegance of the Nimptsch paper is that the effect is found at nutritional doses of vitamin K," he added.
Nimptsch, Rohrmann and Linseisen from the Division of Cancer Epidemiology at the German Cancer Research Centre state that epidemiologic studies of dietary vitamin K intakes have not been conducted in relation to prostate cancer risk.
According to the European School of Oncology, over half a million news cases of prostate cancer are diagnosed every year world wide, and the cancer is the direct cause of over 200,000 deaths. More worryingly, the incidence of the disease is increasing with a rise of 1.7 per cent over 15 years.
A food frequency questionnaire was used to assess habitual dietary intakes at the start of the study, with vitamin K intakes divided into phylloquinone (vitamin K1) and menaquinones (vitamin K2) and total and advanced prostate cancer in the Heidelberg cohort of the European Prospective Investigation into Cancer and Nutrition.
The researchers documented 268 incident cases of prostate cancer during the 8.6 years of follow-up. Of these, 113 cases were classified as advanced prostate cancer. While no reduction in the risk of prostate cancer was observed for vitamin K1 (phylloquinone), an increased intake of all menaquinones (vitamin K2) was associated with a 35 per cent reduction in risk. However, the researchers stated that this association was "non-significant".
Furthermore, a strong association was documented when they considered only advanced prostate cancer, with increased intake of menaquinones linked to a 63 per cent reduction in risk.
While dietary sources of menaquinones include meat and fermented food products like cheese, and natto, Nimptsch and co-workers report that menaquinones from dairy had a stronger inverse association with advanced prostate cancer than did menaquinones from meat.
"Our results suggest an inverse association between the intake of menaquinones, but not that of phylloquinone, and prostate cancer," concluded the researchers. "Further studies of dietary vitamin K and prostate cancer are warranted."
Independent expert comment
Commenting on the research, Dr. Vermeer told this website that the data, in addition to being consistent with other reports in the literature, "the beneficial effect of the long-chain menaquinones has previously been reported for cardiovascular disease; this specific form of vitamin K2 is characterized by preferential transport (via LDL) to extra-hepatic tissues (such as prostate and arterial vessel wall), and by very long half-life times (three days versus 1.5 hours) as compared to vitamin K1 and the short-chain menaquinone-4.
"I am highly pleased by this paper, which underpins the (widely underestimated) importance of long chain menaquinones for disease prevention," Dr. Vermeer told this website.
"It also supports my opinion that intake of vitamin K2 supplements may have a significant contribution to public health."
There are two main forms of vitamin K: phylloquinone, also known as phytonadione, (vitamin K1) and menaquinones (vitamins K2). K1 is found in green leafy vegetables such as lettuce, broccoli and spinach, and makes up about 90 per cent of the vitamin K in a typical Western diet; while K2, which makes up about 10 per cent of Western vitamin K consumption and can be synthesised in the gut by microflora.
Menaquinones (MK-n: with the n determined by the number of prenyl side chains) can also be found in the diet; MK-4 can be found in animal meat, MK-7, MK-8, and MK-9 are found in fermented food products like cheese, and natto is a rich source of MK-7.
MK-4 is distinct from other MKs because it is not a major constituent of the spectrum of MKs produced by gut microflora, but can be derived from K1 in vivo.
A synthetic form of vitamin K, known as K3, does exist but is not recommended for human consumption.
The vitamin is less well known than vitamins A to E, but this increasing body of research, as well as increased marketing and advertising from supplement makers, is raising public awareness of vitamin K.
Source: American Journal of Clinical Nutrition
April 2008, Volume 87, Number 4, Pages 985-992
"Dietary intake of vitamin K and risk of prostate cancer in the Heidelberg cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC-Heidelberg)"
Authors: K. Nimptsch, S. Rohrmann, J. Linseisen