title: A minimum of six days of diet recording is needed to assess usual vitamin K intake among older adults.
abstract: There is a growing interest in the role of vitamin K in health, especially in aging populations. Knowledge of inter- and intra-individual variability of dietary vitamin K intake could be useful to accurately assess usual intake and rank participants in epidemiological studies. Our objectives were to: 1) estimate the variance components of vitamin K intake; 2) investigate whether day of the week, season, and energy intake are factors related to intra-individual variance; and 3) calculate the requisite number of days to achieve desired degrees of accuracy for estimating individual vitamin K intake, ranking individuals and estimating regression coefficient. Vitamin K intake was assessed in 939 older adults (67-84 y) enrolled in the Québec Longitudinal Study on Nutrition and Successful Aging study using 2 sets of 3 nonconsecutive multiple-pass 24-h dietary recalls (24HR) collected 6 mo apart. Each set included 2 weekdays and one weekend day. Intra- to inter-individual variance ratios for vitamin K intake were 3.2 (95% CI = 2.6-3.9) overall, 2.6 (95% CI = 2.1-3.5) for men, and 3.7 (95% CI = 2.9-5.0) for women. Day of the week (weekdays) and season (May to October) were positively and significantly associated with vitamin K intake but explained a negligible part of intra-individual variation (<1%). Adjusting for energy intake explained <7% of variance and did not affect the variance ratio. Six to 13 24HR are required to properly rank individuals according to their usual vitamin K intake and limit attenuation of the regression coefficient. These results should be considered in studies planning to assess vitamin K intakes in older adults.
authors.affiliation: Centre de recherche, Institut Universitaire de Gériatrie de Montréal, Montréal, QC, Canada.
authors.forename: Nancy
authors.initials: N
authors.lastname: Presse
authors.forename: Hélène
authors.initials: H
authors.lastname: Payette
authors.forename: Bryna
authors.initials: B
authors.lastname: Shatenstein
authors.forename: Carol E
authors.initials: CE
authors.lastname: Greenwood
authors.forename: Marie-Jeanne
authors.initials: MJ
authors.lastname: Kergoat
authors.forename: Guylaine
authors.initials: G
authors.lastname: Ferland
mesh_terms: D000368:Aged; D004032:Diet; D015930:Diet Records; D002149:Energy Intake; D005260:Female; D006801:Humans; D008297:Male; D015596:Nutrition Assessment; D011792:Quebec; D012621:Seasons; D012737:Sex Factors; D014812:Vitamin K / Q000008:administration & dosage*
chemical_list: D014812:Vitamin K