Loneliness has been linked to depression and other health problems. It can also spread to others. A friend of a lonely person was 52%more likely to develop feelings of loneliness. And a friend of that friend was 25% more likely to do the same. Happiness, obesity and the ability to stop smoking can also spread like infections within social groups. Loneliness can affect relationships between next-door neighbors. The loneliness spreads as neighbors who were close friends now spend less time together. The study also found that loneliness spreads more easily among women than men.