After an outcry from scientists and experts, federal officials on Thursday said they would restore funding to the Women’s Health Initiative, one of the largest and longest studies of women’s health ever carried out.
The findings of the W.H.I. and its randomized controlled trials have changed medical practices and helped shape clinical guidelines, preventing hundreds of thousands of cases of cardiovascular disease and breast cancer.
“These studies represent critical contributions to our better understanding of women’s health,” said Emily G. Hilliard, a spokeswoman for the Department of Health and Human Services.
“We are now working to fully restore funding to these essential research efforts,” she added. The National Institutes of Health “remains deeply committed to advancing public health through rigorous gold standard research, and we are taking immediate steps to ensure the continuity of these studies.”
The W.H.I., which began in the 1990s when few women were included in clinical research, enrolled over 160,000 participants across the nation. It continues to follow some 42,000 women, tracking data on cardiovascular disease and aging, as well as frailty, vision loss and mental health.
Researchers have hoped to use the findings to learn more about how to maintain mobility and cognitive function and slow memory loss, detect cancer earlier, and predict the risks of other diseases.
H.H.S. had informed the leaders of the research team that it would terminate contracts for the W.H.I.’s regional centers in September, although the clinical coordinating center, based at Fred Hutch Cancer Center in Seattle, would be funded through at least January 2026. As of early Thursday evening, the investigators had not been informed the grants were being restored.
Senator Patty Murray, Democrat of Washington, said shutting down the trial would be “a devastating loss for women’s health research.”
Not only did the initiative lead to major advancements in women’s health, “it has paved the way for a generation of researchers focused on women’s health — which has long been overlooked and underfunded,” Ms. Murray said.
The W.H.I. included a number of randomized controlled trials and has contributed to more than 2,000 research papers. But it is probably best known for a study of hormone replacement therapy that was abruptly halted in 2002, after investigators found that older women who took a combination of estrogen and progestin experienced a small but significant increase in the risk of breast cancer.
Until then, hormone replacement therapy was widely believed to protect women from cardiovascular disease. But the trial found that even though the hormone combination reduced colorectal cancer and hip fractures, it put women at higher risk for heart attacks, strokes and blood clots.
Dr. JoAnn Manson, one of the long-term principal investigators of the study and a professor of medicine at Harvard Medical School and Brigham and Women’s Hospital, called the announcement of funding cuts “heartbreaking.”
The original decision to cut funding, she said, was perplexing, given statements by Robert F. Kennedy Jr., the nation’s health secretary, about the importance of reducing chronic disease in America.
“There is no better example of the scientific impact of research on chronic disease prevention than the W.H.I.,” Dr. Manson said.
The lessons learned from the hormone study have resulted in enormous savings in health care costs, researchers have found — about $35 billion between 2003 and 2012, according to one study, because of the number of cancer and cardiovascular disease cases that had been averted. For every dollar spent on the W.H.I., $140 was saved.
One randomized trial carried out by the W.H.I. looked at the impact of a low-fat diet, high in fruits and vegetables. Though researchers initially found a reduction only in ovarian cancer, long-term follow-up showed that the diet also reduced deaths from breast cancer.
Another study of calcium and vitamin D found that supplements provided a modest benefit for preserving bone mass and preventing hip fractures in older women, but did not prevent other fractures or colorectal cancer.
The findings influenced medical guidelines, which currently do not recommend that all women routinely take the supplements.
The participants in the initiative are now 78 to 108 years old, and some scientists conceded that an argument could be made for winding down the trial. But careful planning is typically given to closing out such a large and wide-ranging study.
“There’s still so much we need to learn,” said Garnet Anderson, senior vice president and director of the public health sciences division at Fred Hutch Cancer Center and a principal investigator of the initiative.
“No one has ever studied 13,000 women over the age of 90 to know: What are their health needs? How to live such a long and health life?” she said. “We’d love to know the secrets of success for healthy aging.”
One reason that the study was begun in the 1990s was that there was a dearth of information and research on women’s health, and little evidence on which to base clinical recommendations, said Marian Neuhouser, who heads the cancer prevention program at Fred Hutch Cancer Center and is chair of the W.H.I. steering committee.
“Women are half the population,” Dr. Neuhouser said, “but they had not been included in research. It had mostly been men, and the results were so-called extrapolated to women.”