Loneliness can spread between friends and acquaintances like an infection, according to a new study. Researchers found that a friend of a lonely person was 52% more likely to feel lonely themselves, while a friend of that friend was 25% more likely. The study examined over 5,000 people in a long-term heart disease study in Framingham, Massachusetts, and established that loneliness spreads through social networks in a pattern similar to happiness, obesity, and smoking cessation.