Massive new research studied over 2 million people to answer a puzzling question about loneliness. Here’s the result

Researchers finally answered a key question.

Here’s a chicken-and-egg question about loneliness and mental health.

• Does loneliness cause poor mental health?
• Or does poor mental health simply make people lonely to begin with?

Researchers have known there’s a correlation, but what they haven’t been able to prove — maybe even rarely thought of trying to prove — is whether one is more likely to cause the other.

It’s a timely question. The World Health Organization’s Commission on Social Connection reported last year that one in six people worldwide experience loneliness, and linked it to roughly 871,000 deaths a year, or about 100 an hour.

Now, a team from the University of Bristol, working with Nesta, Amsterdam UMC, Oxford, and Manchester, has taken a real swing at settling the causation question.

Their study, published in Nature Communications, drew on genetic data from studies covering more than 2 million people, plus data from as many as 414,432 people in the UK Biobank.

Before getting into the findings, it’s worth knowing how they actually measured any of this.

On loneliness, the researchers simply asked participants whether they often felt lonely.

The researchers themselves note this is a blunt instrument, and that a more detailed loneliness scale would likely have picked up stronger effects.

But depression and anxiety were measured using two standard clinical screening tools, the PHQ-9 and the GAD-7, plus separate formal diagnoses pulled from linked NHS medical records.

Self-harm and suicide attempts came directly from linked NHS hospital records (it’s a British study, recall),

As for wellbeing, researchers asked participants to self-report, and applied the answers to scales covering happiness, sense of meaning in life, and overall life satisfaction.

To get past the chicken-and-egg problem, the researchers used three separate methods and checked whether they all pointed the same direction.

First, standard observational analysis, comparing lonely people to non-lonely people.

Second, sibling comparisons, which strip out the effects of growing up in the same household or having similar genes.

Third, something called Mendelian randomization, which uses genetic variants linked to loneliness as a kind of natural experiment, since your genes are fixed at birth and can’t be caused by your mental health later in life.

When all three methods point the same direction, that’s a much stronger case for causation than any one of them alone.

Here’s what they found:

• Loneliness increased the risk of self-harm, suicide attempts, and a depression diagnosis.
• Loneliness increased scores on standard depression and anxiety scales.
• Loneliness lowered happiness, sense of meaning in life, overall wellbeing, and life satisfaction.
• Loneliness also was linked to worse health in general. This also includes a higher chance of having multiple chronic health conditions at once.

The researchers also drew a distinction between loneliness and social isolation.

Social isolation is simply how many people you interact with. Loneliness is how connected you feel, regardless of the headcount.

Someone could spend their days surrounded by people and still feel lonely. You can live alone and not feel lonely at all.

In this study, loneliness came out as the more damaging of the two.

Social isolation on its own was linked to lower happiness and a weaker sense of meaning. However, it didn’t show the same broad effects on depression, anxiety, self-harm, or suicide risk that loneliness did.

Here’s Dr. Zoe Reed, a research fellow at the University of Bristol:

“Our findings suggest that loneliness, and possibly social isolation, are still important public health concerns, especially for mental health and general health.

Supporting people who feel lonely or socially isolated could help improve mental health, wellbeing and overall health.”

The study focused on middle-aged and older adults. The researchers say they can’t be sure whether the same causal pattern holds for younger people.

They also found some evidence the relationship runs both ways.

Poor mental health didn’t just result from loneliness, it also seemed to feed back into it, making people lonelier still. That’s a rough cycle.

So have you been putting off a phone call, a coffee, or a check-in with someone? This might be a good impetus to act.

The upside isn’t abstract. It’s measurable.

Maybe for you and them both.

This post originally appeared at inc.com.

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