The encounter happened years ago, but Beverly K. Brandt remembers it vividly.

She was leaving her office at Arizona State University, where she taught design history, to run an errand for her ailing stepfather. He had moved into a retirement community nearby after his wife, Brandt’s mother, died of cancer.

As his caregiver, Brandt spoke with him daily and visited twice a week. She coordinated medical appointments, prescriptions, requests for facility staff — the endless responsibilities of maintaining a man in his 90s.

Maybe she looked especially frazzled that day, she said, because a longtime colleague drew her aside with a startling question.

“Beverly, why are you doing this?” he said. “He’s not a blood relative. He’s just a stepfather. You don’t have any obligations.”

“I was dumbfounded,” Brandt, 72, recalled. “I still can’t understand it.”

She was 5 when her father died. Three years later, she said, her mother married Mark Littler, an accounting executive and a “wonderful” parent.

“He’d come home from a grueling job, change out of his good clothes, then carry me around the living room on his back,” she recalled. Later, he introduced her to the symphony and the theater, funded her graduate education and mentored her as she entered the academic world.

Even as he descended into dementia, he continued to recognize her and know her name. Why would she abandon him?

But the views her colleague expressed were most likely not unusual. Studies repeatedly show that, unlike the enduring relationship between Brandt and Littler, ties in stepfamilies are usually weaker than those in biological ones.

Because the number of American stepfamilies has steadily risen, sociologists and researchers now worry about a “step gap” that could affect elder care. Given the country’s dependence on family caregivers, the gap could strand many seniors who need help.

“We have more reconfigured families than ever before, and these families may increasingly rely on someone who’s not a biological child,” said Deborah Carr, a Boston University sociologist.

“In general, those relationships tend to be less close. Children are less likely to provide assistance to a stepparent.”

Calculating the growth in stepfamilies isn’t simple, but a demographic analysis published last year estimated that about 16% of Americans over age 70 have at least one stepchild. Among couples in which one partner is over 50, more than 40% do.

This partly reflects the high divorce rate of the 1960s and ’70s, Carr said, but also the more recent growth of “gray divorce,” followed by remarriage or repartnering.

The proportion of older adults in second or later marriages climbed from 19% in 1980 to 30% in 2015. The number of older adults cohabitating, whose family ties also generally prove less close, has soared as well.

“When divorces occur later in life and children are adults, it really changes the equation,” said Merril Silverstein, a sociologist at Syracuse University who has investigated intergenerational relationships.

The age at which a stepparent entered a child’s life, and whether they lived together and for how long, influences the quality of the relationship, studies show.

Brandt’s older brother and sister spent less time in a home shared with their stepfather, she said, and neither developed as strong a relationship with him as she did.

The circumstances that lead to stepfamily formation also play a role. Did a parent remarry after being widowed? Or was the marital dissolution due, instead, to divorce?

How amicable or disruptive was it? How many stepsiblings does a child acquire, and are those relationships supportive or antagonistic?

As parents age, “there’s a lot of negotiation and uncertainties,” Silverstein said. “Who has the right to make decisions for stepparents becomes murky.” Such families can experience what’s called “role ambiguity,” he said, creating doubts about “what the social expectations are.”

Overall, stepchildren provide less care to older adults. A 2021 study led by Sarah Patterson, a sociologist and demographer at the University of Michigan, found “a substantial ‘step gap’” in national data.

Among older adults in need of assistance, almost half of those with only biological children received care from them. Among those in stepfamilies, fewer than a quarter did.

“Even older adults themselves are less likely to expect stepchildren to help them later in life,” Patterson said. Her team found that in stepfamilies, seniors were more likely to get help from partners than those in biological families.

Because stepfamilies are larger, the pool of potential caregivers expands. But a 2019 study found that the decreased likelihood of adult children spending time supporting a stepparent, compared with a biological one, outweighed the increased size of the family network.

Policymakers could encourage elder care within stepfamilies by including them in family-leave laws. Although the federal Family Medical Leave Act explicitly includes stepchildren in its definition of sons or daughters, family definitions vary significantly in the 13 states (and the District of Columbia) that have enacted family-leave laws, and in employer-provided programs.

“Some policies may not clearly include stepchildren, making it challenging for them to access the same benefits as biological children,” Nicole Jorwic, the chief of advocacy for the organization Caring Across Generations, said in an email.

The University of Michigan study determined that the greater likelihood of help from biological children produced no real difference in “unmet needs” — older adults’ inability to handle their personal care because they lacked support. About half of both stepparents and biological parents had unmet needs.

“That points to our larger systemic problem of not supporting families of all types to care for older adults,” Patterson said. Relationships between biological parents in need of assistance and their adult children are hardly free from disappointments and conflicts, after all.

Brandt, wondering to herself what planet her colleague hailed from to warrant such an inquiry, left campus to handle whatever problem her stepfather was experiencing that day. Over 12 years, she supervised his move from the facility’s assisted living section to its nursing home to memory care; she was with him when he died at 98.

“I’d do it all over again,” she said. “In a heartbeat.”

This article originally appeared in The New York Times.

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