Vitamin K intake and hip fractures in women: a prospective study

Background: Vitamin K mediates the gamma-carboxylation of glutamyl residues on several bone proteins, notably osteocalcin. High serum concentrations o f undercarboxylated osteocalcin and low serum concentrations of vitamin K a re associated with lower bone mineral density and increased risk of hip fra cture. However, data are limited on the effects of dietary vitamin K. Objective: We investigated the hypothesis that high intakes of vitamin K ar e associated with a lower risk of hip fracture in women. Design: We conducted a prospective analysis within the Nurses' Health Study cohort. Diet was assessed in 72 327 women aged 38-63 y with a food-frequen cy questionnaire in 1984 (baseline). During the subsequent 10 y of follow-u p, 270 hip fractures resulting from low or moderate trauma were reported. Results: Women in quintiles 2-5 of vitamin K intake had a significantly low er age-adjusted relative risk (RR: 0.70; 95% CI: 0.53, 0.93) of hip fractur e than women in the lowest quintile (<109 mu g/d). Risk did not decrease be tween quintiles 2 and 5 and risk estimates were not altered when other risk factors for osteoporosis, including calcium and vitamin D intakes, were ad ded to the models. Risk of hip fracture was also inversely associated with lettuce consumption (RR: 0.55; 95% CI: 0.40, 0.78) for one or more servings per day compared with one or fewer servings per week), the food that contr ibuted the most to dietary vitamin K intakes. Conclusions: Low intakes of vitamin K may increase the risk of hip fracture in women. The data support the suggestion for a reassessment of the Vitami n K requirements that are based on bone health and blood coagulation.