Author: Yukihiro Ikeda, Masayuki Iki, Akemi Morita, Etsuko Kajita, Sadanobu Kagamimori, Yoshiko Kagawa and Hideo Yoneshima
Publication: Journal of Nutrition. 136:1323-1328, May 2006
Osteoporosis is an important disease, which mainly affects women after the menopause. Nutrition plays an important role in the prevention of osteoporosis. Intake of calcium, magnesium, vitamin D and protein play an important role. Recently there is evidence that also vitamin K may play a protective role. Vitamin K exists in two forms: phylloquinone (found in plants) and menaquinone-7 (produced by bacteria). Natto, a typical Japanese fermented soy product may help to prevent osteoporosis. Natto contains large amounts of menaquinone-7: about 350 microgram per 40 g. Epidemiological studies have already illustrated that Japanese women have lower rates of hip fractures then Western women. Other studies have already shown that intake of menaquinone, at rather high dosage, resulted in less bone mass density reduction.
The aim of the study was to investigate the relationship between natto intake and bone mineral density in healthy Japanese women. The body mass index of 994 women was measured at the spine, hip and forearm at baseline and after a period of 3 years. The researchers found that the body mass index of postmenopausal women increased with increasing dietary intake of natto. More specifically they found that natto intake resulted in reduced bone loss at the femoral neck and the distal third of the radius. No significant association was found between intake of other soy products and evolution of bone mass index. Natto is also rich in isoflavones, which may prevent osteoporosis through its estrogenic action. Natto contains higher levels of isoflavone aglycones than unfermented soy products such as tofu, which contains mainly isoflavone glycosides.
The study concluded that natto intake may help to prevent osteoporosis of postmenopausal women through the action of menaquine-7 or bioavailable isoflavones. More studies are required to eliminate the possible effect of protein and energy intake, and to determine whether the main protective effects of natto come from menaquinone-7 or isoflavones.