Let’s think about the various sorts of people we have some relationship with. I’ll start: there’s my wife, brother, parents, other family members, friends, coworkers. But there are also former coworkers, my doctor, the people I talk to only on social media, the owner of the vegan café…

Taking stock of my social life, I could sort these into crude groups such as ‘family’, ‘friends’ or ‘business’. But relationships are complicated, and there are surely more revealing ways to compare and contrast them. Much as personality models like the Big Five offer a distilled language for describing individuals – slightly introverted, highly conscientious, etc – a model for relationships might be useful for thinking and talking about the shades of difference.

So I was intrigued to read about a proposed ‘unified framework’ for capturing how people see relationships. Researchers asked people from 19 world regions to rate the features of various types of relationships, ranging from siblings to leader and follower to fans of opposing sports teams. They found that relationships could be described in terms of five main dimensions:

• Formality: roughly, how formal and public a relationship is vs informal and private;
• Activeness: how close and involved vs distant;
• Valence: how friendly vs hostile;
• Exchange: how much it involves trading concrete resources like money vs intangible things like affection; and
• Equality: how equal each person’s power is in the relationship.

While the researchers say this model is ‘far from conclusive’, it does give scientists – and the rest of us – a new lens for considering our relationships and what they mean to us. Was the local bartender with whom I chatted about TV and movies for years a ‘friend’? Maybe, maybe not. But relationship traits like formality and exchange help me think about why there seemed to be more to it than ‘business’.

My twins turned 11 the other day. I’m thankful the endless nappy changing and interrupted nights of their infancy are in the distant past. But there are new stresses, such as becoming an on-call chauffeur – to parties, sleepovers and sports clubs. Then, as now, the end result is similar: I’m frazzled most of the time. Ask me to guess and I’d say that being a parent has probably accelerated my brain age. So you can imagine my surprise when I stumbled upon a new paper in the journal Social Cognitive and Affective Neuroscience by James K Rilling and colleagues that claims caregiving – including being a dad – is associated with having a brain that’s young for your age.

The study builds on past research that found mothers and fathers in their 50s had a younger ‘brain age’ compared with their childless peers – by about half a year. This was based on measures of their brain structure, such as white- and grey-matter volume, as judged against databases of hundreds of brains of various ages. The new study extended this pattern to grandmothers and people caring for someone with dementia, and the findings suggested the brain age benefit might be even greater later in life. Compared with controls, grandmothers and caregivers had brain ages that were between four and six years younger, on average (after adjusting for other factors such as income and BMI). Both the old research and the new suggest there’s a sweet spot – too many (grand)kids or too much stress and the brain benefits are reduced.

As to why caregiving is associated with lower brain age, the researchers propose various reasons, such as being more mentally and physically active, the emotional connection, and the sense of meaning and purpose that comes from being a caregiver. My brain feels tired, but it’s nice to know the responsibilities of parenthood might be keeping it youthful!