Loneliness has emerged as a significant health threat.

Surgeon General Dr. Vivek Murthy declared in May that our “epidemic of loneliness and isolation has been an underappreciated public health crisis.”

And new research finds that the number and frequency of social contacts in healthy older adults is linked to brain volume.

People with the fewest social contacts had smaller brains, while people who had the most connections had larger ones.

Specifically, the temporal lobe, occipital lobe, cingulum, hippocampus and amygdala were smaller in people who had less social interaction, according to a study published last month in the journal Neurology.

“Social isolation has been associated with … premature mortality, increased risk of coronary heart disease and stroke, increased reporting of depressive symptoms, as well as increased dementia risk,” Dr. Alexa Walter and Dr. Danielle Sandsmark of the University of Pennsylvania wrote in an accompanying editorial.

To understand the impact of social contact on brain health, researchers from Kyushu University in Japan studied 8,896 elderly men and women and compared their MRI brain scans.

The study participants were also asked how often they’re in contact with friends or relatives who did not live with them (every day, several times a week, several times a month or seldom).

The people with the fewest social contacts had overall brain volume that was significantly lower than those with the most social interaction.

Additionally, socially isolated people had more white matter lesions — areas of damage in the brain — than people with frequent social contact.

“While this study is a snapshot in time and does not determine that social isolation causes brain atrophy, some studies have shown that exposing older people to socially stimulating groups stopped or even reversed declines in brain volume and improved thinking and memory skills,” study author Toshiharu Ninomiya told Neuroscience News.

This research adds to a growing number of studies confirming that loneliness is a serious public health problem worldwide.

In July, a study revealed that lonely diabetics are more prone to cardiovascular disease than the general population. In fact, isolation was found to have more influence on diabetes patients than depression, smoking, physical activity or diet.

A study released in June suggested there may be a link between cancer sufferers who have strong support groups and higher rates of survival.

And it isn’t just the elderly or sickly who feel the effects of social isolation: Gen Zers may be feeling it the most. About eight in 10 report feeling isolated — twice the rate of senior citizens.

“Given the significant health consequences of loneliness and isolation, we must prioritize building social connection the same way we have prioritized other critical public health issues such as tobacco, obesity and substance use disorders,” Murthy stated.

“Together, we can build a country that’s healthier, more resilient, less lonely and more connected.”