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Recruitment

Approximately 65,000 participants were recruited into the EPIC-Oxford cohort between 1993 and 1999. Participation in the study required the completion of a diet and lifestyle questionnaire which consists of a food-frequency questionnaire (FFQ) as well as questions on health, family medical history and four dietary categorisation questions: “Do you eat meat?”, “Do you eat fish?”, “Do you eat dairy products?”, “Do you eat eggs?”. On the basis of the response to these four questions, each participant was categorised as either a meat-eater, fish-eater (does not eat meat but does eat fish), vegetarian (does not eat meat or fish) or vegan (does not eat any animal products). Two methods of recruitment were used: General Practice (GP or nurse) recruitment and postal recruitment.

General Practice recruitment

Recruitment from the general population was carried out by EPIC nurses working in GP surgeries in Greater Manchester, Oxfordshire and Buckinghamshire. Men and women aged 35 and over on the collaborating GP’s list were invited to participate. Questionnaires were mailed to invited participants and appointments were made to attend the GP’s surgery for an interview with the nurse. Each participant consented to provide a blood sample and for further information to be provided from his or her medical records. The nurse then took anthropometric (body size) and blood pressure measurements and a 30ml blood sample, and also checked the completed questionnaire. 

In addition, a pilot recruitment phase was conducted by collaborating GPs in Scotland, who recruited 900 women aged 40 to 59 from those attending the surgery. Each woman completed the detailed health and lifestyle questionnaire at the surgery, and consented to provide a blood sample and for further information to be provided from her medical records. The GP took anthropometric and blood pressure measurements and a 30ml blood sample.

Postal recruitment

The aim of the postal method was to recruit as many vegetarians as possible. Information about the study and questionnaires were sent to members of the Vegetarian Society of the UK, the Vegan Society, and previous participants in the Oxford Vegetarian Study, and also distributed through health related magazines and health food shops. Potential participants were invited to complete the questionnaire after reading the information about the study. Participants recruited by this method were asked on the questionnaire if they would consent to the study team obtaining information from their NHS medical records. They were also asked if they would be willing to provide a blood sample. If they agreed their GP was approached to take a blood sample on behalf of EPIC-Oxford.

Participants

The main questionnaire was completed by 57,496 participants. Data from a shorter version of the questionnaire were available from an additional 7,993 participants. Participants were recruited throughout the UK, with 85% from England, 10% from Scotland, 4% from Wales and 1% from Northern Ireland. The cohort is made up of

23% men and 77% women.

53% of the men are meat-eaters, 12% are fish-eaters, 28% are vegetarians and 7% are vegans.

51% of the women are meat-eaters, 17% are fish-eaters, 39% are vegetarians and 3% are vegans.

Blood samples

Blood samples were provided by 19,500 participants. Blood samples were taken using a specially designed blood kit, either by research nurses employed by our group in Oxford and working in General Practice surgeries, or by GPs or  practice nurses. The samples are stored frozen until they are required for laboratory analysis. Analyses examine specific questions on dietary and other factors in relation to long-term health. The results of laboratory analyses are not sent to participants.

Second blood samples

A subset of participants who had given an initial blood sample and completed a follow-up questionnaire were asked to provide a second blood sample. Participants were selected by age, sex and diet group. 1,000 second blood samples were collected and stored frozen until they are required for laboratory analysis. The main purpose of these repeat blood samples is to assess the stability of blood levels of, for example, vitamins, fats and other nutrients.

Approximately five years after completion of the first questionnaire, a follow-up questionnaire was distributed. About 70% were returned completed. This questionnaire provided us with information on changes in diet, lifestyle and health.

A second follow-up questionnaire was sent in 2007, approximately 10 years after the participants joined the study. About 61% were returned completed.

A third follow-up questionnaire was sent in 2010, approximately 15 years after the participants joined the study. About 65% were returned completed.

Food diaries

Approximately six months after receipt of the completed questionnaire each participant was sent a 7-day food diary in which to record details of everything consumed over a seven day period. 32,000 completed diaries were received. A second 7-day food diary was sent to participants in 2007/2008. The food diaries are coded for analysis as required. 

 

European collaboration

EPIC-Europe is a collaboration between 23 centres in 10 European countries. The centres involved and the numbers of participants in each country are shown in this map. See the EPIC-Europe website for further information.

EPIC-Europe is conducting a large number of analyses on the associations of diet with cancer risk, with a focus on the most common cancers such as cancers of the stomach, colorectum (large bowel), breast, prostate and lung.

A range of papers describing the characteristics of EPIC-Europe participants, dietary methods used, and the  diversity of diets in Europe is available in a supplement to the journal Public Health Nutrition, vol 5. No 6(B). Dec 2002.

So far, research has focused on the role of fruit and vegetables, dietary fibre, meat, fish, dairy products and alcohol intake, as well as dietary-related factors such as obesity and physical activity, on cancer risk. More details of the findings from EPIC-Europe are found in the EPIC-Europe publications.

Participants in EPIC

 

Participants with questionnaire

Participants with questionnaire and blood

End of participant recruitment

Britain

76041

40901

1999

Denmark

57100

56800

1997

France

72000

24000

1993

Germany

55000

53000

1998

Greece

24200

24104

1999

Italy

47822

47822

1998

Netherlands

40659

36924

1998

Norway

34000

10000

2001

Spain

41529

40040

1996

Sweden

57932

57932

1996

Total

506283

391523

acknowlegements

We thank all the participants in this study for generously helping us in this research. We also thank all the doctors, nurses and other practice staff who have kindly assisted us by collecting blood samples from participants. EPIC-Oxford is supported by the Medical Research Council and Cancer Research UK.