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WHI Extension Study 2005-2010


The first WHI Extension Study enrolled consenting participants from each of the original WHI study components for an additional five years of follow-up, from 2005 to 2010. Annual updates on health outcomes are collected by mail from the 115,400 participants enrolled in the Extension Study. The purpose of the additional follow-up is to describe the longer term effects of the original interventions, to document change in hormone use in participants from the Hormone therapy Trials, to expand the range of scientific questions that can be reliably addressed in the WHI, and to provide an infrastructure able to support additional investigations requiring some of the unique features of a very large longitudinal study of postmenopausal women.


Between 1993 and 1998, more than 161,000 women between 50 and 79 years of age were enrolled in the Women’s Health Initiative (WHI), one of the largest studies on the health of postmenopausal women ever done. These participants were scheduled to complete study activities in March 2005. At that time, participants were invited to join the WHI Extension Study, for an additional 5 years of follow-up. The longer follow-up will provide important information on outcomes that might be affected by study treatments only many years after the initiation of intervention, and on outcomes that were too uncommon for clear results to emerge during the initial follow-up period.

WHI Study Design

The original WHI study design was composed of two primary study components: a Clinical Trial (consisting of the Dietary Modification Trial, the Hormone Therapy Trials, and the Calcium/Vitamin D Trial) and an Observational Study. All participants enrolled in one or more components of WHI who were willing to provide written informed consent for extended follow-up were eligible for the Extension Study.

WHI participants were invited to join the Extension Study at either the final WHI clinic visit/contact (CT) or in the final annual follow-up mailing (OS). Efforts to recruit women were standardized to avoid differential accrual between randomization groups and components. For the Extension Study, participating women continue to be associated with the same components and randomization assignments in which they were originally participating in WHI. See Extension Study Consent Status by Study Component and Arm for the number of participants who joined the Extension Study by component, and Extension Study Consent Status by Age and Race/Ethnicity for data on age and race.

The primary health outcomes of interest remain as originally defined for the Clinical Trials. To support the broader scientific objectives of the Extension Study, information on additional health events are ascertained when information about these diagnoses can be reliably obtained through self-report within the available resources.


All Extension Study participants complete annual data collection forms primarily by mail, using procedures similar to those used to collect follow-up data from Observational Study participants during the initial WHI. Women reporting study outcomes are contacted by WHI field center staff to obtain additional detail on health event dates and providers, and a signed release to obtain medical records, if needed. Outcomes documentation is then distributed to physician adjudicators who follow existing WHI procedures for adjudicating cases.

During the extension period, all participants receive an annual WHI newsletter. The purpose of the newsletter is to present WHI news and results, to encourage retention of study participants, and to help keep addresses up-to-date. WHI DM Trial participants who were in the low-fat intervention Dietary Change arm also receive quarterly mailings offering tips for maintaining the low-fat dietary pattern of the WHI DM Trial, if they wish to do so.

Data Collection Forms

All Extension Study participants received an annual Form 33 – Medical History Update by mail; women reporting study outcomes that require documentation are contacted by field center staff to complete a Form 33D – Medical History Update (Details). All participants also received an annual Form 151 - Activities of Daily Life and completed a one-time Form 134 - Medical History Update Addendum.

DM-specific follow-up

A 4.6% subsample of women who were in the WHI Dietary Modification Trial are asked to complete one 24-hour recall during the Extension Study. Half of the subsample completed the recall toward the start of the Extension Study (around 2006-2007) and half toward the end (2009-2010).

HT-specific follow-up

Participants who were in the Hormone Therapy Trial also complete a Form 150 - Hormone Use Update annually. For the first two years of extension follow-up, WHI field centers collected annual mammography reports for HT participants.

Study Consent Forms