Reproducibility and relative validity of a food frequency questionnaire to estimate intake of dietary phylloquinone and menaquinones
This study aims to investigate the reproducibility and relative validity of the Dutch food frequency questionnaire (FFQ), to estimate intake of dietary phylloquinone and menaquinones compared with 24-h dietary recalls (24HDRs) and plasma markers of vitamin K status.SUBJECTS/METHODS:
In a cross-sectional study among 63 men and 58 women, the FFQ was completed three times over a 1-year period and the reproducibility was calculated over these measurements. Twelve-monthly 24HDR were collected to estimate relative validity. In addition, the relative validity of the FFQ, compared with plasma phylloquinone and desphospho-uncarboxylated matrix Gla protein (dpucMGP), was assessed cross-sectionally among 507 postmenopausal women.RESULTS:
Intraclass correlations showed a good reproducibility, with correlations ranging from 0.65 to 0.83. The relative validity for phylloquinone intake compared with 24HDR was lower for women (rs = 0.28) than men (rs = 0.40). The relative validity, compared with 24HDR, for intake of short-chain menaquinones were ranging between 0.30 and 0.34. Long-chain menaquinones showed good relative validity (rs = 0.60-0.69). Plasma phylloquinone concentrations were weakly correlated with phylloquinone intake (rs = 0.16 (0.07-0.24). Plasma dpucMGP was negatively but weakly correlated with phylloquinone intake (rs = -0.09 (-0.18; -0.01)) and long-chain menaquinones (rs = - 0.13 (-0.21; -0.04)), but not with short-chain menaquinones (rs = -0.04 (-0.13; 0.05)).CONCLUSIONS:
The FFQ is reproducible to rank subjects for phylloquinone and menaquinone intake.The relative validity of our FFQ, compared with 24HDR, to estimate intake of phylloquinone and short-chain menaquinones was low, but the relative validity for long-chain menaquinones was good. The relative validity of our FFQ, compared with plasma phylloquinone and dpucMGP, was relatively low for both phylloquinone and menaquinone intake.