Calling a friend after a long day. Showing up to a neighbor's dinner when you'd rather stay home. Lingering a little longer in a conversation that didn't need to last. Such ordinary, even trivial, moments. But to psychologist Susan Charles, Associate Dean of Graduate Programs in the School of Social Ecology, they may be among the most consequential health decisions a person makes.

Charles has been awarded a $2,550,958 grant from the National Institute on Aging to investigate how the daily rhythms of feeling socially connected, or disconnected, shape the way our bodies and minds hold up over time.

Her project, "Linking Daily Dynamics of Social Connection to Physical and Cognitive Functioning," could fundamentally change how doctors, therapists and public health officials approach loneliness and social isolation.

The health stakes of feeling connected

Most people intuitively understand that having close relationships is good for them. Decades of research confirmed it. But, Charles argues that science has been limited by looking at social connection in only one way - as a fixed trait, a general level of sociability that a person either has or doesn't have.

"Our understanding of social connection and its strong association with health is based largely on studies assessing social experiences using static, trait-like measures of general levels of thoughts and activities," Charles notes. "Yet, feeling socially connected varies from day to day, fluctuating as much as other commonly recognized daily emotional experiences."

In other words, the same person who feels warmly surrounded by community on Tuesday might feel profoundly alone by Thursday.

Charles believes such fluctuations may hold the key to understanding how social life gets under our skin, quite literally.

She draws a vivid picture of what this might look like in an ordinary life.

"Daily decisions to call a friend, or to go to a social function even though you are tired from a long day at work may not seem like health decisions," Charles says, "but these times of social connection influence well-being."

The effects, she explains, are both immediate and cumulative. A shared laugh can ease distress and trigger feelings of safety and contentment. Showing up for a regular dinner with a neighbor means you leave your house, stay physically active and engage in the kind of conversation that demands mental effort - tracking information, forming arguments, retrieving memories. Over time, those moments compound.

"Consistent positive social connection enhance health, affecting myriad health outcomes from physical symptoms to gene expression," Charles adds.

Small daily changes, she points out, have the potential to create a "ripple effect" that contributes to longer-term outcomes - for better or for worse.

To test these ideas, Charles is turning to one of the most extraordinary longitudinal datasets in social science: the Midlife in the United States study, known as MIDUS.

The project draws on two longitudinal daily diary datasets spanning nearly 20 years. In one dataset, participants completed nightly phone interviews every day for a week, across three separate waves in 2002, 2014, and 2023. A second dataset captures two waves of daily diary data spanning about a decade, with waves beginning in 2012 and 2023.

Altogether, the study follows more than 2,900 adults ranging in age from 24 to 97.

In addition to the daily diary interviews, participants completed extensive surveys, underwent cognitive assessments and some even flew to a medical facility where they provided blood and urine samples, completed physical fitness tasks and submitted to a battery of biomarker testing.

"Any single facet of this study is interesting to study," Charles says, "but together we have an unprecedented view into how their daily lives unfold and are related to multiple measures of cognitive, physical and mental health."

Charles will delve deep in her search for evidence of social connection's effects.

The professor and her research team plan to examine cortisol, often called the "stress hormone," with chronically high levels linked to cognitive decline and poor physical health.

Charles also will analyze inflammatory markers, gene expression profiles, and even biomarkers of biological age acceleration - measures of how fast a person's cells are aging relative to their chronological age.

The biological story she hopes to tell connects the social world to a phenomenon scientists call "inflammaging," the age-related increase in chronic low-grade inflammation now understood to play a central role in multiple health conditions, including cardiovascular disease, diabetes, certain forms of dementia and arthritis.

"We will examine biomarkers that have been related to poorer health - chronically high inflammation, high levels of cortisol, and gene expression related to inflammation and viral load - and see how these biomarkers are related to the levels and consistency of daily social connection," Charles explains.

If daily patterns of feeling connected, or disconnected, can be shown to move those biological needles, the implications for preventive medicine could be substantial.

Why age changes everything

The study's age range: from young adults in their mid-20s to nonagenarians. Charles is particularly interested in how the relationship between social connection and health shifts as the body grows more vulnerable.

"We know from nearly 100 years of research that social connections are vitally important for people of all ages," she says. "In this study, we are particularly interested in how patterns of social connection change over time in later life, and how social connections may vary in their relationship with health among people with less robust physical systems."

As chronic illness and functional disability become more prevalent with age, she argues, the stakes of social isolation grow higher - and so does the potential benefit of meaningful daily connection.

The United States Surgeon General has called loneliness and social isolation a public health epidemic, and the COVID-19 pandemic accelerated trends toward isolation that were already underway.

Against that backdrop, Charles sees her study as doing something more than documenting a problem. She wants to change the conversation around it.

"Our research reframes a message from warning people about the risks of social isolation to acknowledging the power of positive social connections," she says. "We will be examining different contexts to reveal when and under what circumstances social connections increase our health."

Her goal is simple but potentially transformative: to make social connection a recognized daily health behavior, as concrete and actionable as exercise or diet.

"Social connection should be listed as a daily health behavior for everyone," Charles says. "Every finding that links social connection to better physical and cognitive functioning will reinforce and strengthen this message, as well as identify those most at risk for both social isolation and for the health risk of lack of social connection."