Friends might be more than a boost to good mental health. They might also be the best medicine. The evidence is in the monkey poop. Let us explain.

You can draw comparisons between the social behaviors of rhesus monkeys and humans. Monkeys and humans hang out with others in their respective species.

The monkeys form relationships with other individuals in the troop. They display affection, even respect. Some experts say they get depressed when separated from siblings, as when a rival ousts the alpha male.

In a study led by a British researcher, scientists focused on a group of 22 male and 16 wild female rhesus monkeys. They observed grooming pairings, using it as an indicator of social connection. Then they checked 50 samples of monkey feces.

Analyzing these droppings, scientists found that the most social monkeys had a greater number of microbes that help fight inflammation.

The more disconnected monkeys carried more of a bacterium that in humans is harmful and can lead to strep throat or pneumonia.

Unraveling cause and effect is extremely difficult. But researchers believe it is possible that social monkeys transmitted the beneficial bacteria during grooming. Or perhaps, like humans, the lonely heart primates are more stressed, which might affect their good microbes.

We’re close to nonhuman primates genetically, so scientists think the findings might have relevance in our own species and its web of friendships and social interactions. This is especially important when so many are glued to smartphones and interact more online than with friends in the flesh.

So, want to improve your health? Hanging out with friends can’t hurt.