In the article ‘You’re Contagious’ in May’s Men’s Health, Chris Woolston refers to a study published in the British Medical Journal that happiness is contagious.

Happiness spreads through social networks like an emotional contagion, according to a study that looked at nearly 5,000 individuals over a period of 20 years. When an individual becomes happy, the network effect can be measured up to three degrees. One person’s happiness triggers a chain reaction that benefits not only his friends, but his friends’ friends, and his friends’ friends’ friends. The effect lasts for up to one year. Conversely, sadness does not spread through social networks as robustly as happiness.

The author make two additional observations. Friends ward off loneliness, (‘people who feel disconnected often alienate their remaining friends’) and help you avoid obesity, (‘Men look to other men for clues about acceptable body sizes’ … ‘people eat more if a nearby stranger is overeating, .. the urge may grow if that glutton is a pal’).

Chris Woolston has a host of articles published on the topic, worth perusing here. As for me, optimism remains the default attitude and socializing with positive people remains job number one.