Where did this statistic come from?

It is remarkable how many times this statistic has been used by media, government officials, businesses, social media influencers, podcasts, and even appeared on a Netflix series. But what is the data source of the statistic? It comes from a 2010 meta-analysis of Social Relationships and Mortality Risk (see Figure), which benchmarked the size of the effect that lacking social connection has on risk for premature mortality against the effect of other known risk factors, including smoking. This study was led by Dr. Holt-Lunstad and her research team.

What does this mean?

There are many factors that contribute to the risk of earlier mortality. Some of these are stronger than others. By looking at their magnitude of effect we can get a sense of which contributes more to our overall risk for earlier death. This evidence suggests that lacking social connection contributes to earlier death to a similar magnitude as many other traditional risk factors—including smoking up to 15 cigarettes per day.

What evidence was used to establish this comparison?

The strength of the effect on mortality was established by identifying independent meta-analyses for each of the comparisons, including smoking. A meta-analysis combines all the available data from several studies, rather than relying on a single study, so it gives us a better sense of the overall evidence. Thus, the effect of social connections on risk for mortality established by Dr. Holt-Lunstad and her team was compared to the effect of other factors established in previous research— using the most robust evidence available.

There are many variations on this comparison, which are accurate?

This comparison has been repeated so many times it has become a bit like the game of telephone, with some versions of the comparison veering off from the original data.

• Loneliness. The original comparison was based on an aggregate across measures of social connection (e.g., social network size, social support, social isolation, etc). Loneliness was among these, but not the only one.

• Two packs of cigarettes. The effect size for smoking was based on moderate levels of daily smoking which was defined as up to 15 cigarettes. Since each pack contains 20 cigarettes, presumably smoking 40 cigarettes per day may have a larger effect; however, the original source does not have a precise estimate of smoking 2 packs a day.

  To be accurate to the original source: “Lacking social connection is comparable to smoking up to 15 cigarettes per day.”

How accurate is this? Has it changed over time?

This comparison was based on the most rigorous data available at the time. Science doesn’t stop and we are continually learning more every day. Many more studies have been published on this topic and there has been remarkable consistency.

The Social Connections and Health Lab is currently working in collaboration with other leading academic institutions to keep the information up to date.

To understand even more, watch Dr. Holt-Lunstad’s TEDx talk "Is Social Disconnection Comparable to Smoking?"