We all know that smoking is a killer. Postmenopausal women are told by their doctors to maintain a healthy weight to reduce their risk of breast cancer. Trans fats have mostly disappeared from our diets.

These groundbreaking interventions are rooted in the Nurses’ Health Studies, which have tracked data on lives and lifestyles — and taken biological samples — from thousands of participating nurses for decades. Now, federal research funding cuts are putting these efforts in jeopardy.

The studies’ biological samples are stored in a network of high-powered freezers, which must maintain temperatures as low as 170 degrees below Celsius. The freezers are filled with liquid nitrogen and maintained by a small staff of research assistants and managers at the Harvard T.H. Chan School of Public Health and Brigham and Women’s Hospital. Grants to operate the biorepository have been terminated.

“These women have given all they can for us,” said biobank manager Janine Neville-Golden of the volunteers whose blood and tissue are stored in the repository and who have given their time over years to answer questionnaires and undergo observation during life changes such as illness and pregnancy. “We’ve got to protect these right now. They’re keys to future health.”

The Nurses’ Health Study, which was started in 1976 and continued through a second cohort, Nurses’ Health Study II, in the late ’80s, has contributed to breakthroughs in diet research, cancer research, and the understanding of hormones in women’s health. The Nurses’ Health Study 3, launched in 2010, includes different types of health workers and, for the first time, male nurses.

In 2010, Chan School researchers Jorge Chavarro, Walter Willett, Janet Rich-Edwards, and Stacey Missmer launched the third study in collaboration with investigators at the Channing Division of Network Medicine at Brigham and Women’s Hospital and Harvard Medical School. This initiative was started in conjunction with the Growing Up Today Study (GUTS), which recruits children of Nurses’ Health II participants and has sought to expand on insights gathered through the previous studies.

In light of the funding cuts, collection of samples for both studies has ceased.

“This is a unique, irreplaceable resource, in many regards,” said Chavarro, principal investigator for both Nurses Health III and GUTS. “There are other biobanks, but this one is unique in scale and associated data.”

Chavarro said that while biological samples are relatively easy to capture, “What makes a biobank useful is the fact that you’re able to connect information from those samples to information about the health of people.”

Many of the participants from Nurses Health I and II — who number in the hundreds of thousands — have given multiple biological samples, including urine, cheek swabs, and blood.

“These samples were first collected when people were young and healthy and contain decades worth of information about people’s lifestyles, and follow-ups,” Chavarro said.

He noted that the Chan School is working hard to find funding to replace the lost federal grants. But without a long-term solution, the essential liquid nitrogen cannot be purchased, and millions of samples will degrade.

“If there’s not a sustainable mechanism to continue paying for the ongoing operations of the biorepositories, we’re going to lose samples,” he said. “It’s probably not going to be this week, but it is not something that can wait forever.”

Chavarro said that there is also a real risk of losing the team that makes specimen research like his possible.

“Operating a biorepository is not just putting samples in a freezer. It requires a lot of specific technical expertise,” he said. “You need to know, how do you store samples under what conditions and you need somebody if there’s a freezer failure — you need people who know how to respond.”

Neville-Golden, who has been with the biorepository for 16 years, manages a skeleton crew responsible for maintaining and pulling samples for research. If something goes wrong with a freezer in the middle of the night, she’s the one who’s called. For her, the project is very much a human endeavor.

“I’ve learned a lot,” she said, from freezer maintenance to the lofty goals of the researchers she works with to test hypotheses against the samples. “It’s not about the money, it’s about service and the greater good.”

Neville-Golden said that her team — a handful of research assistants and a dedicated project manager, Nicole Romero — gets somewhere in the neighborhood of 200 external requests per year to use data from the cohorts.

“There’s a long waiting line to get access to these samples, just because there’s not enough person-power to be pulling out the samples that people want,” she said.

Their team hand-picks samples out of tens of thousands stored in each freezer, thaws them, and makes them research-ready. It’s hard work, but Neville-Golden said she tries to keep in mind the people who gave the samples, and what they hoped when giving of themselves.

“A couple of them we’ve talked to over the years said when we are at work and we see people who are that ill and going through everything that they’re going through, we want to do whatever we can do to stop that, to make things better, to eliminate the pain, the suffering, that kind of thing,” she said. “So it really has been a labor of love.”