Ethnic differences in osteocalcin γ-carboxylation, plasma phylloquinone (vitamin K1) and apolipoprotein E genotype

Objective: To investigate plasma osteocalcin gamma-carboxylation and its relationship to plasma phylloquinone concentration and apolipoprotein E ( apoE) genotype in women from three ethnic groups with differing osteoporotic fracture risk. Design and subjects: Fasted blood samples were collected from postmenopausal Gambian ( n = 50), British ( n = 31) and Chinese women ( n = 23), and 11 premenopausal women in each group from three cross-sectional studies. Results: After adjustment for total osteocalcin, plasma undercarboxylated osteocalcin ( adjusted ucOC) was lowest in Chinese and highest in British women postmenopause ( British vs Chinese 103% higher, P<0.0001; Gambian vs Chinese 66% higher, P<0.01). No differences were observed premenopause. Within each ethnic group, adjusted ucOC was similar pre- and postmenopause. Postmenopause, plasma phylloquinone was higher in Chinese women (1.0 ng/ml) than in British (0.31 ng/ml) and Gambian women (0.36 ng/ml) ( P<0.0001). Premenopause, plasma phylloquinone was higher in Gambian and Chinese women (0.6 ng/ml) than in British women (0.3 ng/ml; P = 0.01). Plasma phylloquinone and adjusted ucOC were inversely related in postmenopausal British women ( R-2 = 32.4%; P = 0.0008). ApoE4 frequency was Gambian 32.6%, British 13.8% and Chinese 6%. A lower adjusted ucOC was associated with apoE2 genotype in British and Chinese women. Ethnic differences in adjusted ucOC persisted after adjustment for phylloquinone and apoE genotype. Conclusion: These preliminary data indicate suboptimal vitamin K status in postmenopausal British compared to Chinese and Gambian women. Ethnic differences in apoE genotype may also influence osteocalcin gamma-carboxylation status. The study highlights the need for larger epidemiological investigations of ethnic differences in vitamin K status and the possible implications to bone health. Sponsorship: This work was funded by the MRC.