Vitamin K-rich soybean product linker to higher BMD in men
MedWire News: Men who eat large amounts of a fermented Japanese soybean product, known as natto, have higher bone mineral density (BMD) than those who only consume a small amount of the product, say researchers.
The association is primarily meditated by the high vitamin K content of the natto, report Masayuki Iki (Kinki University Faculty of Medicine, Osaka, Japan) and colleagues.
"Low vitamin K intake is associated with an increased risk of hip fracture, but reports have been inconsistent on its effect on BMD," the researchers note.
They therefore investigated the association between BMD and intake of natto, which contains vitamins K1 (20 µg per 40 gram pack) and K2 (380 µg per 40 gram pack).
The study included 1662 men aged 65 years and older without diseases or medications known to affect bone metabolism.
Participants reported the number of packs of natto consumed over a 1-week period and were classified into four groups: less than one pack per week, one pack per week, more than onel pack per week, one or more packs per day.
Iki and team found that total hip and femoral neck BMD increased significantly with increasing natto intake, after adjustment for age, body mass index, milk intake, smoking, alcohol consumption, physical activity, and diabetes mellitus.
Indeed, participants in the lowest intake group (<1 pack per week) had a mean total hip BMD of 0.881 g/cm2, compared with 0.903 g/cm2 among those with the highest intake (≥1 pack per day). The corresponding values at the femoral neck were 0.740 versus 0.764 g/cm2
In addition, participants with the highest natto intake had a 56% and 58% reduced risk for low BMD (T-score〉<-1 standard deviation) at the total hip and femoral neck, respectively, relative to those with the lowest natto intake.
However, the associations between BMD and natto intake became nonsignificant when the data were further adjusted for undercarboxylated osteocalcin (ucOC) levels, a biomarker of vitamin K intake. This, say the researchers, suggests that the natto-BMD association occurs as a result of the vitamin K content in natto.
In spite of this finding, "a lack of information on dietary nutrient intake, including vitamin K1 and K2, prevented us from further examining the association [between vitamin K and bone health]," Iki and co-authors conclude.
MedWire (www.medwire-news.md) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2011
By Laura Dean