Nature-based social prescribing eased loneliness in a Barcelona trial, but only the loneliest participants needed the nine-week group.

In parts of Europe, a doctor can now hand a lonely patient a referral to a gardening club or a walking group rather than a course of pills. The practice rests on a belief that had never been tested directly: someone who feels alone needs a real group, run by trained facilitators, to feel better.

Researchers in Barcelona compared that version against a much lighter one, a single half-hour conversation and a list of nearby places to go. After three months the two had done the same amount of good.

Something did separate them, though. It wasn’t the program. It was the state a participant was in on the first day.

Loneliness is common in Spanish cities

About 20% of people in Spain report feeling lonely, and another 29.3% have felt it at moderate or severe levels in the past. In Barcelona alone, roughly 100,000 residents are affected, nearly twice the number counted in 2020.

Social prescribing is the health system’s answer to a problem no pill fixes. A doctor or a social worker connects a patient to something in the community, a choir or a volunteer shift, instead of to a clinic. When the activity happens outdoors, it becomes nature-based social prescribing.

The RECETAS project has been testing that approach in six cities on three continents, Barcelona among them. An English evaluation of green social prescribing found that longer programs helped participants most.

Researchers have linked green space to better mental health for years, and they’ve placed loneliness alongside smoking and obesity as a health risk. Nobody had run the two delivery methods side by side.

Friends in Nature ran for nine weeks

Between January 2023 and June 2024, care professionals screened people in 12 low-income neighborhoods around Barcelona, using one direct question: do you suffer from loneliness? Of 411 adults screened, 320 were randomly assigned, 160 to each arm. The trial was registered in advance.

Four out of five participants were women. The median age was about 63, half had finished no more than basic schooling, and 37.5% lived alone. On an 11-point loneliness scale, the median score at the start was eight.

Half of them joined Friends in Nature, or FiN. They met in groups of eight to 10 with two trained facilitators, for one two-hour session a week over nine weeks.

Each session combined group exercises with an outing chosen by the participants. Their neighborhood had helped create a menu of options that included gardens, parks, riverways, and stretches of coast. On some outings they identified plants and animals, made art from natural materials, or talked about nature photographs.

Laura Coll-Planas, the first author and a researcher at the University of Vic, said the program does three jobs at once.

“FiN combines strategies by building groups with peer support, providing social opportunities that are strengthened by experiences in nature and an empowerment process,” Coll-Planas said.

The other 160 received a 30-minute motivational interview and the same neighborhood menu, to use on their own.

Loneliness fell in both arms

Across everyone in the trial, loneliness dropped by an average of 10.5% after three months. It kept falling after that: 12.3% at six months, and 16.8% at one year. On quality of life, neither arm improved.

At the three-month mark, the two arms differed by 0.3 points on the loneliness scale. The difference was too small to rule out chance.

One number did separate the arms. Sixty-two people dropped out of the lighter arm, compared with 36 from the group arm. Participants most often said they left because they were disappointed with the arm they had been assigned to.

Those who left were just as lonely as those who stayed, but they were in better emotional shape. That likely caused the study to underestimate the group program’s effect.

Starting point decided which worked

The team combined several baseline measures, including stress, anxiety, and life satisfaction, into a single emotional wellbeing score before assigning participants to either group. That score changed the answer.

Participants who came in lonelier and in worse emotional shape did better in the facilitated groups. Participants who came in less lonely and steadier did just as well with the interview and the list of options. Both patterns showed up again at six months and at one year.

Jill Litt, the senior author and a researcher at ISGlobal, put the result in terms of what a city can build.

“Our findings provide novel insights that will advance NBSP as a strategy to build community assets and improve social health in urban populations,” Litt said.

Women and older adults dominated

The trial doesn’t tell you much about men, or about adults in their twenties and thirties, because it barely enrolled any.

Everyone enrolled received an intervention because the researchers decided it would be unethical to leave a group without any support. Participants and facilitators both knew which arm they were in.

Screening turned on a single question, and 11% of the people it flagged didn’t register as lonely on the fuller scale. There’s limited agreement in the field on how large a change on that scale has to be before a person notices it, so the 10.5% figure needs care.

Many participants already scored near the top of the 15-dimension quality-of-life questionnaire, leaving little room to improve. One participant sprained an ankle on a nature walk, the only adverse event recorded.

Helsinki produced a different answer

A Finnish team ran the same program with frail older adults in assisted-living facilities, and there the groups clearly beat the comparison arm on loneliness and improved sleep. Those participants had poor physical function and low independence, and their comparison arm spent less time outdoors.

Same program, two cities, two answers. Litt said that bringing people together around shared experiences in natural spaces “is vital for generating the ingredients for a life well-lived – with purpose, belonging and meaning.”

For a health service deciding where to spend, the expensive option is worth reserving for the people who need it. What no one yet knows is whether the light-touch version holds up beyond a year, or whether it only ever suited people who were doing better to begin with.

Researchers are now studying friendship with the seriousness given to diet and sleep, and they’re tracing what isolation does to the brain. Which version to hand to whom is a separate question.

Answering it means running this comparison among men, among younger adults, and among people whose loneliness has lasted long enough to become the ordinary shape of a week.

The full study was published in the journal The Lancet Regional Health – Europe.

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