Information about dietary intake was collected during the baseline home visit (1998-2002) using a nurse-administered FFQ (dietary questionnaire can be found on CLOSER Discovery.
The FFQ was modified from the European Prospective Investigation of Cancer (EPIC) questionnaire. This FFQ has been previously validated for use in a UK population [21].
The FFQ includes 129 food groups and foods and asks the participants to record the average frequency of consumption (never, <1/month, 1-3/month, 1/week, 2-4/week, 5-6/week, 1/day, 2-3/day, 4-5/day, ≥6/day) over the 3 months preceding the interview.
The frequencies of consumption of foods not listed on the FFQ were recorded if they were consumed ≥1/week. Daily amounts of milk and sugar consumed were also recorded. Prompt cards listing example foods included in each food group were used to help standardise responses to the FFQ.
At the end of the FFQ, participants were asked about their use of dietary supplements during the previous three months. If they answered yes to using supplements, further details including the name and brand of the product as well as dose and frequency of use were requested.
A total of 954 different dietary supplements were used by the cohort participants [22]. A shorter version of this FFQ was developed to assess diet quality in later data collections in Hertfordshire, including a sub-group of the participants in the East Hertfordshire follow-up (N=442) studies as part of the European Study of Osteoarthritis (EPOSA) [23, 24].
24-hour food diaries were also collected at baseline but they have not been used in any publications. In 2014, a series of focus groups to explore the influences on diet were held among 92 participants aged 74-84 years whose diets had already been assessed twice; once in 1998-2001 and once in 2011 [25].
