Over a million women have volunteered to share details about their health and lifestyle as part of this study. This wealth of data allows researchers to examine long term trends and causes of disease, improving the understanding of how conditions can be prevented and treated.

Why was this work needed?

We know that lifestyle choices can impact on someone’s health, but researchers need to study large groups of people over long periods of time to really understand what the significant effects are. For example, it is important to know how decisions, like whether or not a woman chooses to take Hormone Replacement Therapy (HRT), might affect their health so that they can make informed choices. At the time the study began, very many women were using HRT but not enough was known about the benefits and risks.

What happened?

Women in England are routinely invited for NHS breast screening between the ages of 50 and 70. Between 1996 and 2001, at one of 66 participating NHS Breast Screening Centres, they were also invited to join the Million Women Study. Along with their screening invitation, women received a study questionnaire, which they were asked to complete and return at the time of screening. Around 70% of those attending the programme returned their questionnaire and agreed to take part in the study.

Women who completed the recruitment questionnaire provided signed consent, and supplied information for follow-up.

Since recruitment, participants have been followed up from their NHS medical records and through update questionnaires. Without such long term, complete follow-up through routinely-collected medical records it would not be possible to provide reliable answers to outstanding health questions on a large scale.

What were the benefits?

Initially, the Million Women Study’s main aim was to look at the impact of hormone replacement therapy (HRT) on breast cancer. However, over time, its remit has expanded and it now supports studies looking at a wide range of lifestyle factors and conditions, including cardiovascular disease and diabetes. For example, recent research has looked at the link between diabetes and cataract surgery, and whether or not there is a connection between unhappiness and ill health.

Around 1 in 4 UK women in the target age group are taking part on the Million Women Study, making it the largest study of its kind in the world. This allows the study to look at conditions and risk factors that are relatively uncommon in the population as a whole. For example, recent research was able to study women with lung cancer who had never smoked.

What type of data was involved?

Participants submit questionnaires about their health and lifestyle (e.g. smoking, weight, diet) and researchers, with consent, also access NHS data on deaths, cancer registration, hospital admissions, cancer screening and some primary care records. Some participants have also given blood and DNA samples.

The study was originally approved by the NHS Anglia and Oxford ethics committee. All participants gave written consent and permission for access to their medical records for follow-up. Researchers obtain updated ethical approval for all relevant additional aspects of the study.

Who funded and collaborated on this work?

The Million Women Study is funded by Cancer Research UK and the Medical Research Council, with support from the NHS and with additional funding for specific projects (e.g. from the Health and Safety Executive).

Where can I go for more information?

The Million Women Study