This video from the Danish Road Safety Council teaches that wearing a bicycle helmet has always been a good idea. From Ads of the World:
The Danes love their bikes, and the Danish capital of Copenhagen is the world’s most cycle-friendly city. One problem, helmets have never become as popular as cycling itself. To combat this, the Danish Road Safety Council launches a campaign which pokes gentle fun at those who are too vain to wear a helmet, by recruiting a group that wore theirs with pride - the Vikings.