The French E3N cohort was initiated in 1990 to investigate the risk factors associated with cancer and other major non-communicable diseases in women.

The participants were insured through a national health system that primarily covered teachers, and were enrolled from 1990 after returning baseline self-administered questionnaires and providing informed consent. The cohort comprised nearly 100 000 women with baseline ages ranging from 40 to 65 years.

Follow-up questionnaires were sent approximately every 2-3 years after the baseline and addressed general and lifestyle characteristics together with medical events (cancer, cardiovascular diseases, diabetes, depression, fractures and asthma, among others). The follow-up questionnaire response rate remained stable at approximately 80%.

A biological material bank was generated and included blood samples collected from 25 000 women and saliva samples from an additional 47 000 women.

Ageing among the E3N cohort provided the opportunity to investigate factors related to agerelated diseases and conditions as well as disease survival.

Who is in the cohort? In June 1990, a questionnaire was sent to 500 000 women who had been born between 1925 and 1950 and were insured by the Mutuelle Générale de l'Education Nationale (MGEN), a national health insurance plan that primarily covers teachers. The questionnaire was sent along with a leaflet explaining that an Inserm research team was launching a study of cancer risk factors and that participation would require filling in questionnaires every 2-3 years as well as the submission of a signed consent form providing permission to obtain information about each participant's vital status, address changes and medical expense reimbursements from the insurance plan. Nearly 100 000 women volunteered.

How often have they been followed-up? Until now, nine follow-up questionnaires have been sent every 2-3 years from the baseline. Approximately half of the answers were obtained after the first mailing. Two reminders were sent thereafter. The questionnaires were accompanied with newsletters that informed participants about the major results obtained to date. The participation rate remained high (77-92% according to the questionnaires) and the lost to follow-up rate was minimal because of the ability to trace non-respondents through their insurance plan files. The questionnaires were accurately filled in, with few missing or unacceptable answers.

What has been measured? To date, 11 self-administered questionnaires have been sent. The collected data are sociodemographic factors, anthropometric measurements, reproductive factors, hormonal treatments, health behaviour and lifestyle. Each follow-up questionnaire also recorded the participant's health status. The questionnaires are available at www.e3n.fr .

The questionnaires are anonymous and identified with an identification number and pin code that can be rapidly scanned to identify the respondents. The questionnaires are optically scanned and all answers are checked on screen. The scanned images are saved to allow data entry at a later time, including information regarding the addresses of medical doctors (18 000 to date) or drug names (pre-listed to avoid errors). The longitudinal data (repeats of identical questions for the purpose of updating information about topics such as menopause or smoking) are routinely homogenized. Several validation studies (e.g. dietary and anthropometrical data studies) have been performed and have revealed very satisfactory results.

Self-reported cases of cancer are validated and coded after reviewing the pathology reports obtained from medical practitioners, and nearly 90% of all cancer cases are histologically confirmed. Other diseases are also validated (e.g. diabetes, myocardial infarction, stroke, Parkinson disease) by requesting additional information about the participants (e.g. glycosylated haemoglobin levels, fracture-related circumstances, drug names) and sending questionnaires to medical doctors.

Additionally, a biological material bank was generated. Blood samples were initially collected from 1994-99. The participation rate among the invited participants was approximately 40%; this yielded approximately 25 000 blood samples that were each separated into 28 aliquots (e.g. plasma, serum, leukocytes, erythrocytes). Plastic straws were used to store each participant's samples in liquid nitrogen containers. The bio-repositories are located at the IARC (Lyon) and the EFS (Etablissement Français du Sang, Annemasse). Since 2004, approximately 10 case-control studies have been conducted (approximately 1 800 cases and 3 500 controls) with regard to the measurements of various biomarkers (e.g. fatty acids, calcium, vitamin D, vitamin B, cholesterol and C-reactive protein). A metabolomics study is currently ongoing.

From 2009-11, saliva samples (Oragene, DNA Genotek, Kanata, ON, Canada) were requested from 68 242 living women and were obtained from 47 000 women (participation rate, 69%). Salivary DNA has been extracted and has been used for genotyping in two case-control studies (approximately 2 500 cases and 850 controls) since December 2010.

The research team is currently planning to set up a tumour tissue bank and will begin with the collection of breast cancer tissues.

What has it found? The E3N cohort has produced a spectrum of results regarding the complex roles played by nutrition, hormonal factors, physical activity, anthropometric characteristics and other major lifestyle-related factors with respect to various diseases.

Inclusion Criteria:

• only women
• born between 1925 and 1950
• insured by the Mutuelle Générale de l'Education Nationale (MGEN)

Exclusion Criteria:

- men

The cohort comprised nearly 100 000 women with baseline ages ranging from 40 to 65 years, all insured through a French national health system (MGEN).