After an outcry from scientists and health experts, federal health officials said Thursday that 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 WHI 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 spokesperson 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 WHI, 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.

HHS had informed the leaders of the research team that it would terminate contracts for the WHI’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.

The WHI 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.

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 WHI,” 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 WHI, $140 was saved.